Working Group on Marine Mammal Ecology (WGMME)

ICES SCIENTIFIC REPORTS RAPPORTS SCIENTIFIQUES DU CIEM ICES INTERNATIONAL COUNCIL FOR THE EXPLORATION OF THE SEA CIEM CONSEIL INTERNATIONAL POUR L’EXPLORATION DE LA MER WORKING GROUP ON MARINE MAMMAL ECOLOGY (WGMME) VOLUME 3 | ISSUE 19 International Council for the Exploration of the Sea Conseil International pour l’Exploration de la Mer H.C. Andersens Boulevard 44 –46 DK -1553 Copenhagen V Denmark Telephone (+45) 33 38 67 00 Telefax (+45) 33 93 42 15 www.ices.dk info@ ices.dk ISSN number: 2618 -1371 This document has been produced under the auspices of an ICES Expert Group or Committee. The contents therein do not necessarily represent the view of the Council. © 2021 International Council for the Exploration of the Sea. This work is licensed under the Creative Commons Attribution 4.0 International Licence (CC BY 4.0). For citation of datasets or conditions for use of data to be included in other databases, please refer to ICES data policy . ICES Scientific Reports Volume 3 | Issue 19 WORKING GROUP ON MARINE MAMMAL ECOLOGY (WGMME) Recommended format for purpose of citation: ICES. 2021. Working Group on Marine Mammal Ecology (WGMME). ICES Scientific Reports. 3:19. 155 pp. https://doi.org/10.17895/ices.pub.8141 Editors Anders Galatius • Anita Gilles Authors Markus Ahola • Matthieu Authier • Steven Benjamins • Sophie Brasseur • Andrew Brownlow • Julia Carlström • Peter Evans • Andrea Fariñas • Ruth Fernandez • Steve Geelhoed • Jan Haelters • Philip Hammond • Ivar Jussi • Mart Jussi • Karl Lundström • Kjell Tormod Nilssen • Iwona Pawliczka • Marie Petitguyot • Graham J. Pierce • Maris Plikshs • Rui Prieto • Janneke Ransijn • Bob Rumes • Debbie Russell • Sophie Smout • Camilo Saavedra Penas • Jose Antonio Vazquez Bonales • Abbo van Neer • Mikhail Verevkin • Gregg Verutes • Markus Vetemaa • Cécile Vincent • James Waggitt ICES | WGMME 2021 | i Contents i Executive summary .......................................................................................................................iv ii Expert group information .............................................................................................................. v ToR A: Review and report on any new information on seal and cetacean population abundance, population/stock structure, management frameworks (including indicators and targets for MSFD assessments), and anthropogenic threats to individual health and population status ............................................................................................................................................. 1 1.1 New abundance and distribution information ................................................................ 1 1.1.1 Seal abundance and distribution ..................................................................................... 1 1.1.1.1 Abundance, Iceland ......................................................................................................... 4 1.1.1.2 Abundance, Baltic Sea ...................................................................................................... 5 1.1.1.3 Abundance, Atlantic Scandinavia ................................................................................... 10 1.1.1.4 Abundance, Continental coast, Wadden Sea to France ................................................. 12 1.1.1.5 Abundance, UK and Republic of Ireland ........................................................................ 16 1.1.1.6 Abundance, North America ........................................................................................... 20 1.1.1.7 New information on seal distribution ............................................................................ 22 1.1.2 Cetaceans ....................................................................................................................... 23 1.1.2.1 Passive acoustic monitoring (PAM) of harbour porpoises in the Baltic Sea .................. 23 1.1.2.2 Visual monitoring and strandings .................................................................................. 25 1.2 New information on population/stock structure ........................................................... 39 1.3 Management frameworks (including indicators and targets for MSFD assessments) .................................................................................................................. 39 1.3.1 Seal management frameworks ...................................................................................... 39 1.3.1.1 OSPAR Convention ......................................................................................................... 39 1.3.1.2 HELCOM ......................................................................................................................... 40 1.4 New information on anthropogenic threats .................................................................. 40 1.4.1 Update on cumulative effects ........................................................................................ 40 1.4.2 Foodweb ........................................................................................................................ 40 1.4.2.1 Baltic Sea ........................................................................................................................ 40 1.4.2.2 Norway ........................................................................................................................... 41 1.4.2.3 Poland ............................................................................................................................ 41 1.4.2.4 Ireland ............................................................................................................................ 41 1.4.2.5 Predation of marine mammals by grey seals - methodological advances ..................... 41 1.4.3 Fishery bycatch .............................................................................................................. 42 1.4.3.1 Potential biological removal of seals ............................................................................. 42 1.4.4 Pollution ......................................................................................................................... 43 1.4.5 Marine debris ................................................................................................................. 45 1.4.6 Underwater noise .......................................................................................................... 45 1.4.7 Climate ........................................................................................................................... 50 1.5 References ..................................................................................................................... 50 2 ToR B: Review foraging areas and estimate consumption by harbour seal, grey seal and harbour porpoise in the North Sea case study area .................................................................... 59 2.1 Outline ........................................................................................................................... 59 2.2 Example studies ............................................................................................................. 68 2.2.1 Grey seal diet in the North Sea based on analysis of scats from UK haul-out sites ....... 68 2.2.2 Harbour seal diet in the Kattegat–Skagerrak area ......................................................... 72 2.2.3 Minke whale diet in the North Sea ................................................................................ 73 2.2.4 Diet studies in German waters....................................................................................... 73 2.3 Methodology for generating diet information for WGBIODIV ...................................... 74 2.3.1 Estimates for prey guild modelling ................................................................................ 74 2.3.1.1 Geographical and temporal distribution ........................................................................ 74 ii | ICES SCIENTIFIC REPORTS 3: 19 | ICES 2.3.2 Predator diets for ECOPATH North Sea modelling......................................................... 75 2.4 Discussion ...................................................................................................................... 76 2.5 References ..................................................................................................................... 77 3 ToR C: Review selected aspects of marine mammal-fishery interactions, assemble data and qualitative information available from other sources not fully covered by WGBYC (including strandings, entanglement, interviews, research projects, national/local monitoring) on marine mammals ................................................................................................ 82 3.1 Legislation and organizations involved in managing bycatch ........................................ 82 3.1.1 International organisations addressing bycatch of marine mammals in the NE Atlantic ........................................................................................................................... 82 3.1.2 Acoustic Deterrent Devices Regulations for marine mammal bycatch mitigation ........ 85 3.1.3 Review of EU and US legislation requirements for monitoring marine mammal bycatch ........................................................................................................................... 88 3.1.3.1 Policy background .......................................................................................................... 88 3.1.3.2 Legal requirements for monitoring bycatch .................................................................. 88 3.1.3.3 Challenges and lessons learnt ........................................................................................ 89 3.2 Reviews of recent publications and reports .................................................................. 90 3.2.1 Summary of FAO Guidelines to Prevent and Reduce Bycatch of Marine Mammals in Capture Fisheries....................................................................................... 90 3.2.2 Summary of WWF report on using camera technology to monitor, and support mitigation of, wildlife bycatch in fisheries ..................................................................... 92 3.2.3 Summary of ASCOBANS Reports .................................................................................... 94 3.2.4 Summary of the Progress Report on the Jastarnia Plan: The Recovery Plan for the Harbour Porpoise in the Baltic Proper (Carlén and Evans, 2020) ............................ 95 3.2.4.1 Threats and population status ....................................................................................... 95 3.2.4.2 Public Awareness in the Baltic ....................................................................................... 96 3.2.4.3 Stakeholder involvement and cooperation ................................................................... 97 3.2.5 Key Conclusions and Recommendations ....................................................................... 97 3.2.6 Review of recent publications on bycatch and other interactions with fisheries - Interviews with fishers ................................................................................................... 97 3.2.6.1 Economic quantification of damage .............................................................................. 98 3.2.6.2 Description of interactions ............................................................................................ 99 3.2.6.3 Bycatch estimates ........................................................................................................ 100 3.2.7 Review of information on bycatch of marine mammals in Macaronesia and in the Mediterranean ....................................................................................................... 100 3.3 Forthcoming and current initiatives to reduce bycatch ............................................... 104 3.3.1 Entanglement and marine mammals-the Scottish entanglement Alliance programme .................................................................................................................. 104 3.3.2 Towards a coordinated assessment and monitoring strategy for marine mammals: project proposal for Bay of Biscay and Iberian Coast................................. 106 3.3.3 Mediterranean bycatch projects ................................................................................. 107 3.4 New tools ..................................................................................................................... 108 3.4.1 Bycatch Risk Assessment (ByRA) Toolbox .................................................................... 108 3.4.2 Use of social media as a data source on bycatch ......................................................... 109 3.5 Aquaculture and marine mammals-a Scottish perspective ......................................... 110 3.5.1 Direct mortality ............................................................................................................ 110 3.5.2 Entanglement ............................................................................................................... 111 3.5.3 Acoustic impacts .......................................................................................................... 111 3.5.4 Vessel-based disturbance/collision.............................................................................. 112 3.5.5 Wider ecosystem effects.............................................................................................. 112 3.5.6 Conclusion .................................................................................................................... 113 3.6 Questionnaire on stranding networks in Europe ......................................................... 113 3.6.1 Data sharing ................................................................................................................. 113 ICES | WGMME 2021 | iii 3.6.2 About the strandings networks ................................................................................... 114 3.6.3 Attending strandings .................................................................................................... 121 3.6.4 About the stranded animals ........................................................................................ 123 3.6.5 Processing stranded animals ....................................................................................... 126 3.6.6 Necropsies ................................................................................................................... 129 3.6.7 Bycatch-specific information ....................................................................................... 134 3.6.8 General comments by respondents ............................................................................. 138 3.7 References ................................................................................................................... 138 4 ToR D: Update the database for seals ....................................................................................... 146 4.1 The “ICES/WGMME seal database” ............................................................................. 146 4.2 Other species and missing areas .................................................................................. 146 4.3 References ................................................................................................................... 149 Annex 1: List of participants........................................................................................................ 150 Acknowledgements ................................................................................................................... 152 Annex 2: Resolutions .................................................................................................................. 154 Working Group on Marine Mammal Ecology (WGMME) .......................................................... 154 iv | ICES SCIENTIFIC REPORTS 3:19 | ICES i Executive summary The Working Group on Marine Mammal Ecology met in 2021 to address new information on marine mammal ecology relevant to management. Two terms of references were standing ToRs; under the first of these, ToR A, new and updated information on seal and cetacean population abundance, population/stock structure, management frameworks as well as anthropogenic threats to individual health and population status were reviewed along with findings on threats to marine mammals such as bycatch, pollution, marine debris and noise. ToR B is a cooperation with WGBIODIV to review species-specific foraging distributions (considering horizontal and vertical dimensions depending on data availability) and to estimate consumption by marine mammal species representative in case study areas. ToR C was implemented to review aspects of marine mammal fishery interactions not covered by ICES WGBYC. ToR D is the second standing ToR and concerns updating the WGMME seal database, which was updated with the latest data. Regarding ToR A, seal stocks in the North Atlantic are generally growing and stable, except both grey and harbour seals in Iceland, which have both declined dramatically in recent decades. Also, harbour seals in some areas of northern UK are declining, and the southern Baltic ringed seal subpopulation is threatened by climate change. Suggestions for calculation of Potential Biological Removal (PBR) for grey seals in OSPAR regions I, II and III are also provided. Recent surveys for estimating cetacean species abundance are presented as well as updates on anthrophonic threats, such as pollution. Under ToR B it was emphasized that when estimating diet and prey consumption of marine mammals, aspects like (1) non-representativeness of samples (e.g. stomachs from stranded or bycaught individuals or scats from seal haul outs) for the population, (2) not recoverable remains of some prey items and (3) the partially (and maybe completely) digestion of hard prey remains in the gastro-intestinal tracts of the predator, are important to consider. To illustrate the available data and metainformation some example case studies were summarised. An outline methodology for combining and analysing data useful for prey guild modelling and ECOPATH modelling is presented. Under ToR C, Regulations for acoustic deterrent devices to mitigate marine mammal bycatch and legislation requirements for monitoring of bycatch were reviewed along with updated information on bycatch. A questionnaire survey to European stranding networks mapped information pertinent to bycatch assessments. ICES | WGMME 2021 | v ii Expert group information Expert group name Working Group on Marine Mammal Ecology (WGMME) Expert group cycle Annual Year cycle started 2021 Reporting year in cycle 1/1 Chairs Anita Gilles, Germany Anders Galatius, Denmark Meeting venue and dates 1–4 February 2021, Online meeting (30 participants) ICES | WGMME 2021 | 1 ToR A: Review and report on any new information on seal and cetacean population abundance, population/stock structure, management frameworks (including indicators and targets for MSFD assessments), and anthropogenic threats to individual health and population status 1.1 New abundance and distribution information 1.1.1 Seal abundance and distribution In many ICES areas, seal populations are surveyed regularly, providing for a comprehensive long-term monitoring of these pinnipeds. Here, abundances of harbour, grey and ringed seals in the North Atlantic and Baltic are described based on available data. Trends of harp and hooded seals are described in the WGHARP reports (ICES, 2019). Tables 1, 2 and 3 summarise the most recent available seal survey data, analogous to what WGMME has presented in former years. In the following, assessments of population status and developments are presented individually for the different countries/management units and species, including trajectories of (available) counts. Unless it is stated that a figure refers to a population abundance estimate, numbers of seals reported are those counted on haul outs, which do not include seals at sea during surveys. Table 1, Recent harbour seal survey data. Country Survey Year(s) Moult (All seals) Breeding season (Pups) References Norway Nilssen and Bjørge, 2018 North of 62N 2015 3872 South of 62N 2016– 2018 1054 Nilssen and Bjørge, 2019 Finnmark 2012– 2013 981 Skagerrak 2016– 2018 543 Iceland 2018 9434 Granquist and Hauksson, 2019 Wadden Sea 2020 28 352 9954 Galatius et al., 2020 Dutch Delta Area 2018/2019 1184 119 (2018) 8 | ICES SCIENTIFIC REPORTS 3:19 | ICES Figure 4. Trends of moult counts of harbour seals in the Kattegat and the Danish Belt Sea, Southwestern Baltic, Limfjord and Kalmarsund. BALTIC PROPER/KALMARSUND: The harbour seal population in Kalmarsund is genetically divergent from adjacent harbour seal populations (Goodman et al., 1998) and experienced a severe bottleneck in the 1970s when only some 30 seals were counted. Long-term isolation and small numbers have resulted in low genetic variation in this population (Härkönen et al., 2006). The population has increased annually by ca. 9% since 1975 and 2056 seals were counted in 2020 (Swedish Museum of Natural History). Grey seals Monitoring of the grey seal population in the Baltic Sea (Halichoerus grypus ssp. grypus) is based on internationally coordinated censuses during the moulting season, covering the entire Baltic moulting distribution of the species. The maximum number (not corrected for individuals in water) counted during 2–3 replicate surveys in each sea area is used for assessing abundance and trends. The grey seal population in the Baltic has been growing throughout the span of the coordinated surveys (starting in 2003) with the most pronounced growth in the southern and western parts of the moulting distribution (Figure 5). Around 38 000 seals were counted in 2019 and 40 000 in 2020, indicating that the population is still growing (HELCOM EG MAMA). Of the hauled-out population, around 80% were found in the core moulting area in the central Baltic proper (archipelagos of central Sweden, southwestern Finland and western Estonia). Outside the breeding and moulting seasons, grey seals travel and forage in other areas too. As the size of the population has increased, its range has expanded to also include the southern Baltic, where grey seals have been breeding regularly, although in small numbers, since 2003 (Galatius et al., 2020b). In most of the recent years, pups have also been observed Kattegat. (Galatius et al., 2020b). This expansion has brought Baltic grey seals in contact with the Atlantic subspecies, and there are strong indications of hybridisation between the two groups based on microsatellite data from the southern Baltic (Fietz et al., 2016). ICES | WGMME 2021 | 9 Figure 5. Trends for results of moult counts of grey seals in subareas of the Baltic Sea. The annual numbers of grey seals observed during moult surveys in different subareas of the Baltic are shown in Figure 5. Although most short-term changes in regional numbers fit within variation in the proportion of the population hauled out during the survey window, large shifts may describe true changes. One larger shift in the hauled-out numbers was observed from 2019 to 2020; the counts in an area in the Stockholm archipelago in Sweden, which has previously had the largest groups of grey seals, and in the Finnish southwestern archipelago decreased by over 2000 and increased by 1700, respectively. Counts in the area in Finland in 2019 were already over 3000 higher than in 2017. Counts also increased in Estonia by over 1000 from 2017 to 2018. During these years, the hunting pressure in the Stockholm archipelago increased markedly, which is a possible factor behind this apparent shift in distribution. Grey seals use islands for breeding in the Central Baltic in years when the ice cover is limited due to mild winters. The numbers of pups born on land is negatively correlated to the maximum ice cover in the Baltic Sea, as ice is the preferred breeding platform (Jüssi et al., 2008). Pup surveys on the Estonian west coast have been systematic since 1990 and comparison among years without coastal ice during the breeding season in February-March an increasing trend can be observed (Figure 6). 10 | ICES SCIENTIFIC REPORTS 3:19 | ICES Figure 6. Trends of counts of grey seal pups in West Estonia in years without ice in the breeding areas. 1.1.1.3 Abundance, Atlantic Scandinavia Harbour seals The Skagerrak harbour seal population collapsed by roughly 50% during both mass mortality events due to PDV, in parallel with the Kattegat population, in 1988 and 2002. Before the two collapses, the population increased at high rates, indicating no factors retarding the growth. After the latter collapse, the rate of increase has been lower, which may indicate the population approaching carrying capacity. The number of harbour seals along the eastern coast of Skagerrak (starting from the eastern half of the Oslo Fjord in the north) that were counted during the moult was 7300 in 2019 and 4700 in 2020 (Figure 7). The lower result in 2020 is likely to have resulted from a combination of hot weather and high level of disturbance from recreational boats. Along the northern coast of Skagerrak (west of the Oslo Fjord), the harbour seal abundance (animals counted during moult) has decreased from 680 in 2008–2015 to 543 in 2016–2018. South of 62° N, the harbour seal count increased from 860 in 2011–2015 to 1054 in 2018 (Nilssen, and Bjørge, 2019). Counts in the northern Norwegian areas will be finished in 2021. ICES | WGMME 2021 | 11 Figure 7. Trends of moult counts of harbour seals in the Skagerrak and Norwegian coast. Grey seals Since the early 1960s to 2010, the numbers of grey seals have increased in Norway. Based on pup production estimates from 2006 to 2008, a total population (including pups) of 8740 (95% CI: 7320–10 170) animals in 2011 was estimated by modelling (Øigård et al., 2012). However, a significant reduction in pup production has been observed between 62°N and 68°N in Trøndelag and Nordland counties (mid-Norway) in 2014–2018 (Nilssen and Bjørge, 2017). In other areas along the coast, pup production has been stable (Figure 8). A new survey was carried out in midNorway in 2018, which confirmed that pup production was low. The significant reduction in pup production in mid-Norway suggests a dramatic decline in the Norwegian grey seal abundance to a total population of 3850 (95% CI: 3504–4196) individuals, when scaling pup production using a multiplier of 5.7 (Nilssen et al., 2019). The most probable reason behind the reduced pup production is high bycatches of grey seals in gillnet fisheries for mainly monkfish, but also in cod gillnets. 12 | ICES SCIENTIFIC REPORTS 3:19 | ICES Figure 8. Trends of counts of grey seal pups in Norway. 1.1.1.4 Abundance, Continental coast, Wadden Sea to France Harbour seals WADDEN SEA (Denmark, Germany, the Netherlands): Harbour seal surveys in the Wadden Sea are coordinated among Danish, German and Dutch scientists. Brasseur et al. (2018) examined a 40-year time-series (1974–2014) of harbour seal moult counts in the Wadden Sea to study underlying processes of recovery, and demonstrated the influence of historical regional differences in management regimes on the recovery of this population. Mortality rates were close to 50% during both PDV epidemics in 1988 and 2002, and between and after the epidemics, population growth rate has been close to the maximum intrinsic exponential growth rate of harbour seals at 12–13%. Since 2012, the trend appears to have started levelling off with an average annual growth rate of 1.2%. In contrast, pup counts continue to increase (Figure 9). In 2020, almost 28 400 harbour seals were counted during moult surveys (Galatius et al., 2020a). Pup counts are almost at 10 000 pups representing 35% of the moult counts. The cause of this apparent mismatch in trends is unclear. Either mortality in this population is equivalent to the pup production, as there is no growth despite increasing pup production, or a substantial change in haul-out behaviour has occurred which could affect the survey results. Either way, there is a clear indication of a recent change in the population. ICES | WGMME 2021 | 13 Figure 9. Trends of counts of moulting harbour seals (left) and harbour seal pups (right) in the Wadden Sea. Results from Brasseur et al. (2018) indicate interesting exchanges between the different regions of the Wadden Sea with disproportionally high pup production relative to moult counts in the German states, while after the breeding period, seals redistribute throughout the area. As the entire Wadden Sea area is monitored synchronously, lack of growth is unlikely to be an artifact of redistribution of the animals. Future efforts should concentrate in understanding the mechanisms underlying these changes in population trends. SOUTHERN NETHERLANDS, BELGIUM and FRANCE. The growing harbour seal colony in the Dutch Delta area in the southern Netherlands is thought to be part of the Wadden Sea population as there are not enough local births (119 pups in 2019) to explain its growth (Figure 10). Moreover, although there is a lack of systematic stranding data, an average of 80 dead harbour seals are reported annually in the area. Telemetry data show regular exchange between this area and the Wadden Sea. Over 1184 animals were counted in the Dutch Delta area in 2018 (Hoekstein et al., 2020), and numbers have been growing at almost 15% annually since 2002. Similar exchanges might occur with French and southern English colonies. In 2020, seal counts amounted to 1167 harbour seals in the colonies on the French coast from Normandy to the Belgian border (data compiled by Poncet S.; data owners: Office Français de la Biodiversité, SYMEL CDL, ADN, GDEAM-62, GMN, Bretagne Vivante, Picardie Nature, Réserve naturelle nationale du Domaine de Beauguillot (PNRMCB), Syndicat Mixte Baie du Mont-Saint-Michel, Maison de l'estuaire, CMNF, RNN des Sept-Iles / LPO). Until 2015, the average rate of increase of harbour seals in the Northeast Channel (southern North Sea) was 15% per year (Vincent et al., 2017), but from 2017 to 2020, the maximum number of harbour seals counted during the moult in the main colonies of the area seems to level off (around 600 seals). Recent telemetry tracking of both harbour and grey seals from the Baie de Somme have confirmed the movements of grey seals between the North Sea and the eastern Channel on one hand, and the shorter, coastal movements of harbour seals on the other hand (Figure 11). Windfarm projects are planned in the Channel along the French coasts, and more tracking and monitoring of the seal colonies are planned in both the eastern Channel and Normandy in the coming years. In Belgium, there are no true seal colonies; however, tens of animals strand annually along the coasts (48 in 2019, dead and dying, and excluding seals that were taken to a rehabilitation facility). The number of harbour seals observed hauling out in Belgium, especially in the port of Nieuwpoort, is rising and seals are seen daily. In 2020, 19 harbour seals were observed hauled out (exceeding previously recorded numbers). These are frequently joined by juvenile grey seals 14 | ICES SCIENTIFIC REPORTS 3:19 | ICES (three in 2020). As in previous years, multiple animals were injured by fishing gear including hooks and rope (RBINS unpublished.; Haelters et al., 2020). Figure 10. Trends of counts of moulting harbour seals and harbour seal pups in the Dutch Delta and French and Belgium Coast. Figure 11. Tracking of 15 harbour seals (left) and 12 grey seals (right) from the Baie de Somme (France) in 2019/20. Each colour represents one individual. The arrows show the capture site. Grey seals After centuries of practical absence, grey seals have shown a remarkable recovery in the Wadden Sea area, where more than 7600 were counted during the moult in 2020 (Brasseur et al., 2020). In the same area, 1726 pups were counted in the winter of 2019/2020 (Brasseur et al., 2020; Figure 12). Colonies started in Germany and the Netherlands in the 1970s and have since expanded to Denmark. The growth rate is higher than likely based and autochthonous recruitment and is thus deemed to be partially fuelled by immigration from the UK (Brasseur et al., 2015). Up until 2020, the majority of the grey seals counted in the Wadden Sea were counted in the Netherlands (>70%), while recently counts in the German Wadden Sea (especially Helgoland and the ICES | WGMME 2021 | 15 Kachelotplate) have grown in importance (>20%), as have the numbers in Denmark (>5%). During the breeding season, the proportion of pups born in Germany is proportionally more important (almost 40%) compared to the moult counts. Figure 12. Trends of moulting grey seals and grey seal pups in the Wadden Sea. The difference in relative distribution might be indicative of the importance of the exchange with the UK population. Possibly seals from the UK use the Dutch area more than other parts of the Wadden Sea. As with harbour seals, grey seal numbers have been growing in the Dutch Delta area, despite there being no pups produced (until 2018 when ten pups were born), and an apparent high mortality rate (~40 deaths reported per year). The continuous growth in grey seal numbers suggests a constant exchange between this area, the Wadden Sea and the UK, where numbers are growing. In 2019, a maximum moult count of 1593 grey seals in the Delta area was reported (Hoekstein et al., 2020, In France, there are also breeding colonies, and numerous exchanges with the UK and the Wadden Sea have also been recorded using telemetry. Occasionally a few grey seals (two) are seen to haul out on the Belgian coasts. The maximum moult count along the French coasts was 1350 in 2020, and on the breeding sites, 75 pups were observed (Figure 13). (Data compiled by Poncet S.; data owners: Office Français de la Biodiversité, SYMEL CDL, ADN, GDEAM-62, GMN, Bretagne Vivante, Picardie Nature, Réserve naturelle nationale du Domaine de Beauguillot (PNRMCB), Syndicat Mixte Baie du Mont-Saint-Michel, Maison de l'estuaire, CMNF, RNN des Sept-Iles / LPO). 16 | ICES SCIENTIFIC REPORTS 3:19 | ICES Figure 13. Trends of moult counts of grey seals (left) and grey seal pups (right) in the Dutch Delta Area and France and Belgium Coast. 1.1.1.5 Abundance, UK and Republic of Ireland Harbour seal Scotland, Northern Ireland and Southeast (SE) England account for the majority of UK harbour seals, with only small populations elsewhere (South England, Northeast England). A recent study (Carroll et al., 2020) combining genetic, movement and population trend data indicated that the UK population belongs to two distinct metapopulations: northern (Scotland, Northern Ireland) and southern (SE England) with the latter being part of the continental Europe group. These metapopulations encompass differing population trends. Harbour seal populations in the UK are primarily monitored via August moult counts largely at the scale of Seal Management Units (SMUs). Surveys are conducted annually, with the aim of covering the Scottish and English SMUs within a five-year period. More frequent surveys are conducted in areas of continuing decline (e.g. Orkney), and the populations in SE England, and in the Moray Firth and Firth of Tay in East Scotland are surveyed annually. The UK harbour seal population has remained reasonably stable over the last 25 years; the latest UK count total from surveys conducted between 2016 and 2019 was 31 744 (Morris, Duck and Thompson, 2020), giving rise to an estimated population of 44 100 (approximate 95% CI: 36 100– 58 800). Counts in the northern metapopulation show varying trends from continuing decline (Orkney and North Coast, East Scotland SMUs), depleted but stable (Shetland, Moray Firth), stable (Western Isles, Southwest Scotland) with indications of an increase (West Scotland) (Figure 14). The latest counts (2019) covered Orkney, Shetland and the northern section of the Moray Firth SMU, completing the round-Scotland survey round, which started in 2016 producing an overall count of 26 846. This is just over 5% higher than the previous Scotland census in 2011– 2015, but almost 10% lower than the highest Scotland total counted in 1996–1997. The latest count of 1012 (2018) in Northern Ireland indicates little change in population since the previous count in 2011 (948). Research is ongoing into the proximate and ultimate cause of the declines in Scotland. The rate of decline suggest that they are, in part, due to increased adult mortality. Ultimate causes under investigation are biotoxins, grey seal competition and predation. The UK component of the southern metapopulation, almost entirely in SE England SMU, had been showing sustained increases, punctuated by PDV epidemics in 1988 and 2002. However, the latest SE England count of 3752 (2019) was approximately 25% lower than the counts of the last three years and similar to the post epidemic minimum counts in 2004–2006. This is driven by a particularly low count for The Wash, a Special Area of Conservation (SAC), which until 2019 accounted for around 75% of the southeast population. Given the substantial variation in ICES | WGMME 2021 | 17 the proportion of the population hauled out, further data are urgently required to confirm the decline and quantify the rate. The reasons behind such levelling off and potential decline are unclear, but the relative abundance of grey seals may be a factor; the ratio of harbour: grey seals in SE England SMU has changed from 10:1 in 1988 to 1:10 in 2019. Pup counts have been conducted within this SAC between 2001 and 2019. Although the pup production trend had been increasing, there is evidence this may have levelled off in recent years (Thompson, 2019). In the Republic of Ireland, 4007 harbour seals were counted in August 2017 and 2018, using aerial thermal imaging (Figure 17). This number represents an increase relative to the two previous surveys of 2003 (3489 seals) and 2011-2012 (2955 seals). As in previous surveys, most seals were counted in the west region. Figure 14. Trends of moulting harbour seals in the subareas of the UK. Grey seal The UK grey seal population appears to comprise one metapopulation that extends into the rest of Europe. Indeed, there are considerable movements between UK Seal Management Units, Ireland, and the continent (Brasseur et al., 2015; Carter et al., 2021). Population size is estimated using a Bayesian state–space population dynamics model (Thomas 2020) in which prior information on vital rates (Russell et al., 2020) is combined with two sources of data: (1) a regionspecific time-series of pup production, and (2) ‘independent’ estimates of grey seal population (2008, 2014; independent from pup production) which are derived by combining August counts and an estimate of the proportion of the population available to count (from telemetry data). The population model incorporates ca. 90% of UK pup production and thus the output provides trends, but not absolute estimates, of regional pup production and abundance. Scaling up the output of the population model provides a UK population estimate (individuals of age 1+) in 2019 of 150 700 (approximate 95% CI 130 000–176 100; SCOS 2020). Grey seal moult count trends for subareas in the UK are shown in Figure 15. 24 | ICES SCIENTIFIC REPORTS 3:19 | ICES end in May 2021. In addition to 15 long-term monitoring stations using C-PODs located from the Island Fehmarn to the Pomeranian Bay, ten more stations were deployed in 2020 for four months (same positions as in 2018). At a subset of these, SoundTraps and F-PODs were deployed additionally to C-PODs. The recorded acoustic data will be compared to visual data collected by aerial surveys in the same area and during the same period. The project is funded by the Federal Agency for Nature Conservation. POLAND: No national monitoring for harbour porpoises was carried out in 2020, but is planned to be carried out for a full year starting in March 2021. Outside the national monitoring programme, Hel Marine Station of the University of Gdańsk continues on a project to obtain data on seasonal distribution and occurrence of harbour porpoises in Polish coastal waters. The project covers waters along the entire Polish coast up to 3 nm offshore, which is the zone where most of the static nets are used by small boats of the Polish fishing fleet. The data collection started in October 2020 and will continue for a period of one year. The data will be compared with previously obtained PAM data from two subareas (Vistula Spit in 2013–2014 and Puck Bay in 2017–2018), where the majority of direct bycatch data have been reported by fishermen. SWEDEN: The national monitoring programme of harbour porpoises is funded by the Swedish Agency for Marine and Water Management and carried out by the Swedish Museum of Natural History (SMNH). Data on detection rates are publicly available at Sharkweb, hosted by the Swedish Meteorological and Hydrological Institute (https://sharkweb.smhi.se/). In the Baltic Sea, continuous PAM using C-PODs has been carried with smaller adjustments since 2017. In 2020, 11 previous SAMBAH stations were monitored. An analysis of trends in acoustic detection rates during SAMBAH (2011–2013) and the national monitoring programme (2017–2020) has been carried out and a manuscript was submitted in 2020 (Owen et al., in review). In 2019, the national Swedish monitoring programme was extended to also include continuous PAM at 14 stations located in five Natura 2000 in the Kattegat Sea. The results from the first to years of monitoring are to be evaluated in 2021. In addition to the national monitoring programme in Sweden, regional monitoring of harbour porpoises is also carried out by some counties. In 2020, a coordinated regional monitoring programme was initiated, within which both F-PODs and C-PODs are to be deployed in 2021. Also, regional PAM data are to be uploaded to Sharkweb. In 2020, the HELCOM Expert Group on Marine Mammals (EG MAMA) took the first steps towards including processed data from PAM programmes of harbour porpoises in the HELCOM Biodiversity database. The aim is to upload national PAM data available from HELCOM Contracting Parties in 2021. In the development of a common reporting format, it has become evident that the methods for data collection and processing varies slightly among the countries, whereby the data to be uploaded will not be harmonised across all countries. Further work is needed to achieve this. In July 2020, a concept note for a SAMBAH II project was submitted to the EU LIFE programme and a full application is prepared to be submitted in February 2021. The German Federal Agency for Nature Conservation (BfN) is project coordinator, and the full application includes partners in all countries around the Baltic Sea except Latvia and Russia. The project aims to provide an updated abundance estimate for the Baltic Proper harbour porpoise population, harbour porpoise density surface maps for the Baltic Sea, FRV and GES abundance thresholds for both the Belt Sea and Baltic Proper harbour porpoise populations, estimated impacts by anthropogenic activities, and recommendations for future management and monitoring. ICES | WGMME 2021 | 25 1.1.2.2 Visual monitoring and strandings BELGIUM: The Royal Belgian Institute for Natural Sciences (RBINS) completed two aerial surveys in 2020. During the survey in June, 34 porpoises were observed, yielding an estimate of on average 0.56 (0.37–0.77) animals/km² in Belgian waters. During the survey on 1–2 September, 37 porpoises were observed, yielding a similar average density: 0.55 (0.36–0.78) animals/km². The only other cetacean observed during the surveys was a solitary bottlenose dolphin (Tursiops truncatus). As in previous years, a solitary bottlenose dolphin was regularly observed in Belgian waters, adjacent to French waters. There was one observation of a group of four bottlenose dolphins. There was one observation of a minke whale (Balaenoptera acutorostrata) and, unrelated to the sighting, one stranding. One very decomposed common dolphin washed ashore and a very decomposed white-beaked dolphin (Lagenorhynchus albirostris) was found at sea. In total, 66 harbour porpoises washed ashore or were found dead in rivers or ports (data RBINS). At least four of these stranded alive (all died shortly after stranding). Causes of death of the porpoises (preliminary data) were (probable) bycatch (3), grey seal predation (12, with at least four that survived an attack but died from their injuries and/or infection afterwards) and other natural cause (11). The most remarkable strandings were those of two Sowerby’s beaked whales, which are very rare in Belgium. A juvenile female stranded -probably alivein January, and another juvenile female washed ashore dead in August, one day after efforts to refloat the animal that had entered a port. DENMARK/ GERMANY/SWEDEN: In a joint effort of the three countries, a new population abundance survey (MiniSCANS-II), by means of aerial surveys, for the Belt Sea porpoise population has been conducted in June–July 2020. The results will be reported at WGMME 2021. GERMANY: In spring 2020, a total of 432 harbour porpoise groups (561 animals, 71 calves) were recorded along 2641 km of effort in five areas in the North Sea (Dogger Bank, Area B, Sylt Outer Reef West, Sylt Outer Reef East, Weser-Elbe estuary, Figure 1a). In summer 2020, a total of 245 harbour porpoise groups (320 animals, incl. 25 calves) were observed under 2237 km of effort in four areas in the North Sea (Sylt Outer Reef West, Sylt Outer Reef East, Weser-Elbe estuary, Borkum Reef Ground, Figure 1b). One sighting of minke whale (single animal) and one sighting of white-sided dolphins (Lagenorhynchus acutus, eight animals) were observed in spring near the Dogger Bank. The Baltic Sea was surveyed in one study area (Mecklenburg Bay) in summer 2020 and a total of ten harbour porpoise groups (12 animals, one calf) were sighted along 183 km of effort (Figure 1.1.2.1b). 26 | ICES SCIENTIFIC REPORTS 3:19 | ICES a. b. Figure 1.1.2.3. Survey effort and harbour porpoise sightings during aerial surveys in the German North and Baltic Sea during a) spring 2020 and b) summer 2020. Harbour porpoise group sizes are indicated using group size dependent red circles; yellow stars mark mother–calf pairs; blue lines indicate covered transect lines (i.e. survey effort). ICES | WGMME 2021 | 27 Effort corrected density and abundance estimates, also corrected for availability and perception bias, were generated using a bootstrapping approach. In spring 2020, the German North Sea was largely covered (areas A–E). The total abundance for these areas was estimated to be 44 554 (95%CI: 33 189–59 552) animals, at 1.66 (1.24–2.22) animals/km² (Table 1.1.2.1). In summer 2020, the German North Sea was covered in four of the eight areas (C–F). The total abundance for these areas was estimated of 25 480 (17 855–35 986) harbour porpoises and an average density of 1.09 (0.76–1.54) animals/km² (Table 1.1.2.1). In the German Baltic Sea, where only the Mecklenburger Bay West area was surveyed (K), an abundance of 639 (250–1092) harbour porpoises, corresponding to a density of 0.20 (0.08–0.35) animals/km², was estimated (Table 1.1.2.1). Table 1.1.2.1. Summary of effort corrected, bootstrapped density and abundance estimates for spring 2020, and summer 2020 in the German EEZ of the North and Baltic Seas. N = estimated abundance of harbour porpoises; N95%CI = 95% confidence interval around N; D = density estimate of harbour porpoises in animals/km²; D95%CI=95% CI around D; s = average group size. Area Season N N95% CI D D95% CI ŝ Dogger Bank (A) spring 2020 11 425 8011–16 093 2.02 1.42–2.85 1.25 (B) spring 2020 9209 6149–13 075 2.33 1.56–3.31 1.40 Sylt Outer Reef West (C) spring 2020 18 677 12 139–27 808 3.12 2.03–4.64 1.34 Sylt Outer Reef East (D) spring 2020 3318 1819–5111 0.48 0.26–0.74 1.31 Weser-Elbe estuary (E) spring 2020 1925 916–3298 0.44 0.21–0.75 1.10 North Sea Areas: Dogger Bank (A) (B) Sylt Outer Reef West (C) Sylt Outer Reef East (D) Weser-Elbe estuary (E) spring 2020 44 554 33 189–59 552 1.66 1.24–2.22 1.31 Sylt Outer Reef West (C) summer 2020 9929 6249–14 850 1.66 1.04–2.48 1.29 Sylt Outer Reef East (D) summer 2020 9991 5806–15 550 1.45 0.84–2.25 1.30 Weser-Elbe estuary (E) summer 2020 1467 279–3785 0.34 0.06–0.86 1.60 Borkum Reef Ground (F) summer 2020 4092 2657–5914 0.67 0.44–0.97 1.28 North Sea Areas: Sylt Outer Reef West (C) Sylt Outer Reef East (D) Weser-Elbe estuary (E) Borkum Reef Ground (F) summer 2020 25 480 17 855–35 986 1.09 0.76–1.54 1.31 Baltic Sea Area: Mecklenburger Bay West (K) summer 2020 639 250–1092 0.20 0.08–0.35 1.20 28 | ICES SCIENTIFIC REPORTS 3:19 | ICES Trends in absolute harbour porpoise abundance in the German North Sea till 2020 were investigated by Nachtsheim et al. (2021), based on almost two decades of aerial surveys (2002–2019, spring and summer). The trend analysis was conducted in a hierarchical Bayesian framework to a series of replicated visual surveys, allowing to propagate the error structure of the original abundance estimates to the final trend estimate. In general, harbour porpoise abundance decreased in northern areas and increased in the south. A particularly strong decline with a high probability (94.9%) was detected in the core area and main reproduction site in summer, the SAC Sylt Outer Reef (-3.79% per year). The overall trend for the German North Sea in summer revealed a decrease in harbour porpoise abundance over the whole study period (-1.79% per year) with high probability (95.1%). FRANCE: Two small-scale aerial surveys were conducted in France in 2019–2020. CAPECET and SPEE surveys cover the Bay of Biscay (Figure 1.1.2.2). CAPECET aims to investigate patterns of distribution of small delphinids during the winter months. In particular, CAPECET surveys are conducted when large numbers of strandings occur along the Atlantic seaboard. SPEE is a smaller survey that aims to document seasonal patterns of marine mammal abundance and distribution within a recently designated MPA, the ‘Parc Natural Marin de l’Estuaire de la Gironde et de la mer des Pertuis’. Seasonal abundances were estimated for the two years of SPEE surveys (27 700 km in eight seasons, 2019–2020) for harbour porpoise, common dolphins (Delphinus delphis, including striped or common unidentified), and bottlenose dolphin (Figure 1.1.2.3; Van Canneyt et al., 2020b). During CAPECET survey, 1800 km of effort were sampled four times between mid-January and March 2020. Density was estimated along four session of winter 2020 with a mean value of 0.32 animals/km2 (CV: 0.35) for January–February 2020. Despite a change in distribution pattern with encounter rate spread over the shelf area compare to SAMM survey (January–February 2012) density of small delphinids (striped or common dolphins) over the CAPECET study area was higher with 0.51 animals/km2 (CV: 0.33) for January–February 2012. Mainly driven by pod size with a mean value of 12 individuals in 2012 decreasing to 6.5 in 2020 (Van Canneyt et al., 2020a). In addition, the Airborne optical remote sensing system was deployed in some of these flights to assist the detection and species identification (https://hytech-imaging.fr/stormm/). Data are still being analysed. Virgili et al. (2020) report previous results of 2017–2018 aerial surveys in French, Belgian and English waters in the North Sea. ICES | WGMME 2021 | 29 Figure 1.1.2.4. SPEE and CAPECET transect lines in the French waters of the Bay of Biscay. Figure 1.1.2.5. Densities (animals/km2) of common dolphin (and small sized delphinids (striped or common unidentified) estimated by conventional distance sampling (CDS) for each session of SPEE survey 2019–2020. Encounter rate (sighting/km on 20x20 km grid cell; from Van Canneyt et al., 2020b). 30 | ICES SCIENTIFIC REPORTS 3:19 | ICES Figure 1.1.2.6. Densities (animals/km2) of common dolphin (and striped or common unidentified) estimated by CDS for each session of CAPECET survey (mid-January to mid-March 2020) and encounter rate (sighting/km; from Van Canneyt et al., 2020a). 2012 2020 Figure 1.1.2.7. Encounter rate map of small delphinids (stiped/common dolphin) during SAMM I survey in January–February 2012 (left) and during CAPECET January–February 2020 (right) on 20x20 km grid cells. FAROESE: Gilles et al. (2020) reported on the first fully corrected abundance estimates for the harbour porpoise in the Faroe Islands. Dedicated aerial surveys were conducted in the summer of 2010 in Faroese coastal waters. Only part of the area inside the 300 m depth curve could be surveyed and a total of 1564 km were surveyed in good or moderate porpoise sighting conditions. The total abundance estimate was 5175 porpoises (CV=0.44; 95% CI: 3457–17 637). ICELAND: Pike et al. (2020) summarized the results of aerial surveys in the coastal waters of Iceland conducted in the period 1986–2016. All coastal areas were covered during seven complete aerial surveys in summer, whilst seven partial surveys covered parts of the same area and at different times of the year. New abundance estimates, corrected to the extent feasible for known biases, for common minke whales, humpback whales (Megaptera novaeangliae), whitebeaked dolphins and harbour porpoises from some or all of the 2007, 2009 and 2016 surveys were presented (Table 1.1.2.2). Pike et al. (2020) also examined the distribution of these and other ICES | WGMME 2021 | 31 species in Icelandic waters over the 30-year timespan of the surveys, as well as changes observed over the period. The relative abundance of common minke and humpback whales, and whitebeaked dolphins, was comparatively low in the spring and fall, and peaked in June and July when all of the main surveys have been carried out. An analysis of changes in density as an index of relative abundance from all surveys (1986–2016) indicated that common minke whale abundance decreased by up to 75% after 2001, and has remained at a relatively low level since then. This decrease has been particularly apparent in the southwest and southeast of Iceland, areas that previously had very high densities. Relative abundance of humpback whales and whitebeaked dolphins has increased over the period 1986–2016, particularly in the northern part of the survey area. Estimating harbour porpoise abundance and trend was considered unfeasible except from the surveys conducted in 2007 and 2016, which provide abundance estimates of similar magnitude. Table 1.1.2.2. Abundance estimates of marine mammal species in Icelandic waters. Species abundance estimate of population name of population and reference source Harbour porpoise 43 179 (95% CI 31 755–161 899) Icelandic Waters, 2017 (Gilles et al., 2020) White-beaked Dolphin 159 000 (95% CI 49 957–506 054) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019a) Atlantic White-sided. Dolphin 131 022 (95% CI 35 251–486 981) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019a) Long-finned Pilot Whale 344 148 (95% CI 162 795–727 527) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019) Northern Bottlenose Whale 19 975 (95% CI 5562–71 737) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019) Sperm Whale 23 166 (95% CI 7699– 69 709) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019) Humpback Whale 9867 (95% CI 4854–20 058) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019) Common Minke Whale 23 407 (95% CI 13 035–42 032) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019) Sei Whale 3127 (95% CI 964–10 142) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019) Fin Whale 36 773 (95% CI 25 811–52 392) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019) Blue Whale 3000 (95% CI 1377–6534) Central N Atlantic (Icelandic and Faroese Waters), 2015 (Pike et al., 2019) 32 | ICES SCIENTIFIC REPORTS 3:19 | ICES IRELAND: No surveys have been conducted in 2020. A second series of ObSERVE aerial surveys is foreseen in 2021–2023. NETHERLANDS: No aerial surveys have been conducted in 2020. Following an update of the national conservation plan for the harbour porpoise the monitoring scheme has been changed to triennially in spring and summer (and aiming for a six-yearly SCANS survey) instead of the current annual summer surveys (Ministry of Agriculture, Nature and Food Quality, 2020). In 2020, 431 stranded cetaceans divided over seven species were recorded (www.walvisstrandingen.nl) by Naturalis Biodiversity Center. As usual harbour porpoise was the most abundant species (n =431, Table 1.1.2.3). The number of stranded harbour porpoises in 2019–2020 belong to the lowest in more than a decade (Figure 1.1.2.6). The stranded bottlenose dolphin was a French male that followed a sailing vessel to the harbour of Amsterdam, to be subsequently herded to the North Sea where it died a few days later. Post-mortem investigation indicated it died from a collision with a vessel (IJsseldijk et al., 2020). Table 1.1.2.3. Stranded cetaceans recorded in the Netherlands in 2019. Source: www.walvisstrandingen.nl Naturalis Biodiversity Center. Species N Harbour porpoise 431 unidentified dolphin 1 Bottlenose dolphin 1 Striped dolphin 1 Minke whale 2 Sowerby's beaked whale 1 Bottlenose whale 2 Total 443 ICES | WGMME 2021 | 33 Figure 1.1.2.8. Stranded Harbour Porpoises in the Netherlands per year from 1 July to 30 June annually from 1 July 1990 to 30 June 2020. Source: www.walvisstrandingen.nl Naturalis Biodiversity Center. PORTUGAL: In the Azores, Romagosa et al. (2020) used a five-year acoustic dataset collected by autonomous recorders that were processed and analysed using an automated call detection and classification system, to show that fin and blue whales are present in the Azores Archipelago from September until May with no detections during the summer during autumn and winter months. Sei whales were recorded in spring and autumn, corresponding to their expected migration patterns. SPAIN: Since WGMME reported on the results of cetacean surveys in Spain in 2016 (ICES, 2016) no updates have been provided. For the harbour porpoise, the abundance estimate obtained during SCANSIII in July 2016 in block AC (Hammond et al., 2017), which covered to the Cantabrian sea and northern Galician waters, was reported at 183 (density = 0.005 animals/km2, CV = 1.02, 95% CI = 0–669. The only other estimate available so far, is the one obtained during the Phocoeval project (MartinezCedeira et al., 2016) in September 2015. During ship-based and aerial surveys in the Phocoeval project a total of eight harbour porpoises and 58 common dolphins were sighted in the aerial surveys, while five and 20 sightings respectively were recorded in the ship surveys (Figure 1.1.2.7). Due to the low number of sightings, the abundance of both species combined was estimated, resulting in the following figures from the ship survey (abundance = 1185, density = 0.14 animals/km2, CV = 0.43, 95%CI = 512–2730) and the aerial survey (abundance = 186, density = 0.014 animals/km2, CV = 0.82, 95%CI = 40–854). Martinez-Cedeira et al. (2016) concluded that the differences of one order of magnitude between both estimates are due to the attraction of common dolphins to the boat. 40 | ICES SCIENTIFIC REPORTS 3:19 | ICES 1.3.1.2 HELCOM In the Baltic Sea area HELCOM uses core indicators Population trends and abundance of seals and Distribution of Baltic seals. The evaluation of the indicators is based on the data from the standardized aerial monitoring during the moult and on more scattered information on breeding and foraging distributions. The Population trends and abundance of seals evaluates the state of the seal populations in each management unit. For the grey seal population, there is one management unit covering the whole Baltic population, excluding Kattegat. The harbour seal is evaluated in three management units: Kalmarsund, Southern Baltic and Kattegat. Evaluation for the ringed seal is separate for the Bothnian Bay and the Southern management unit (consisting of three sub-populations). Good status is achieved when the abundance is exceeding the limit reference level (LRL) of 10 000 animals and is growing with a natural rate when under carrying capacity or not decreasing more than 10% over a tenyear period when close to carrying capacity. The core indicator Distribution of Baltic seals reaches good status when the distribution of seals is close to pristine conditions considering haul out sites, breeding sites and foraging areas. The core indicators are evaluated in six-year assessment periods. The most recent indicator reports were published for the period 2011–2016 (HELCOM, 2018a, b). 1.4 New information on anthropogenic threats 1.4.1 Update on cumulative effects In 2019, WGMME conducted a review of theoretical frameworks and approaches for assessing cumulative effects of multiple stressors on marine mammals (ICES, 2019). In this section, we provide a brief update on publications providing additional information for marine mammal cumulative Impact Assessments (CIA). The Interim Population Consequences of Disturbance (iPCoD) framework was developed by SMRU Consulting and the University of St Andrews in 2013 to forecast the potential effects on marine mammal populations in UK waters of any disturbance and permanent hearing loss (threshold shifts, PTS). The iPCoD framework was developed with the quantification of the effect of disturbance on vital rates determined via expert elicitation, conducted in 2013. In 2018, the transfer functions on the effects of disturbance on the probability of survival and of giving birth to a viable young of harbour porpoise, harbour seals and grey seals were updated via a two-day expert elicitation (Booth et al., 2019). Based on new empirical data collected and published since 2013, experts indicated that the effects of disturbance were likely to be less severe than previously estimated. However, it is recommended that research effort is directed to address the knowledge gaps currently estimated using expert elicitation (for both the effects of PTS and disturbance on vital rates). Murphy et al. (2020) showed that life-history traits of harbour porpoises varied between different management units (MUs) and highlight the value of using mortality data as a source of information on demographic parameters. 1.4.2 Foodweb 1.4.2.1 Baltic Sea Kauhala et al. (2020) found that nutritional condition of grey seal pups in April–May was positively correlated with prey quality of herring and sprat. Furthermore, adult size of male grey seals was positively correlated to the herring and sprat quality in their birth year. Hunting pressure (Kauhala et al., 2016) and bycatch (Vanhatalo et al., 2014) may be a factor in increased ICES | WGMME 2021 | 41 mortality, but decreasing birth rate and blubber thickness are linked to decreasing food quality (Kauhala et al., 2016; 2017; 2019) 1.4.2.2 Norway Harbour seals in the Norwegian Skagerrak were found to mainly consume haddock/pollack/saithe, fish from the genus Trisopterus, plaice and herring, with plaice contributing most biomass. Relatively small fish made up most of the diet and cod only contributed 2.3% of biomass, suggesting limited competition with local fisheries (Sorlie et al., 2020). 1.4.2.3 Poland Keszkaa et al. (2020) analysed scats from the Vistula River mouth haul-out in Poland for genetic and osteological analyses of grey seal diet. The most numerous species were perch, zander, lamprey, cod and sea trout. Herring was conspicuous by its absence. Diet seemed opportunistic as contributions varied with seasonal cycles of the different prey species. 1.4.2.4 Ireland Using genetic analyses of scats, Schiønning et al. (2020) found evidence of grey seal consumption of monkfish and salmonids in Ireland, with seasonal and regional variability of occurrence. 1.4.2.5 Predation of marine mammals by grey seals - methodological advances Throughout the past years, several publications have highlighted the need for a detailed assessment of potential ecological effects related to grey seals utilising marine mammals as prey resource (Brownlow et al., 2016; Jauniaux et al., 2014; Leopold et al., 2015; Thompson et al., 2019; van Neer et al., 2020, 2021). One current example is the decline of parts of the UK harbour seal population. Here it remains unclear which role the predation by grey seals plays, but it was shown that the observed decline could already be explained, even if only 1% of the occurring adult males take each six adult harbour seals per year (Thompson et al., 2019). Data from e.g. the Netherlands show that grey seal predation is one of the major causes of mortality in stranded harbour porpoises (Leopold et al., 2015), further highlighting the importance of this topic. In order to assess the ecological effects, it is crucial to establish an internationally standardised assessment scheme allowing for cross-border comparison of data. Besides detailed descriptions of detected lesions and behaviour in case reports (Bishop et al., 2016; Bouveroux et al., 2014; van Neer et al., 2019; 2015), several publications have described patterns of lesions found to be common based on macroscopic assessment of a larger number of carcasses resulting in specific parameters to look for in seals (Brownlow et al., 2016; van Neer et al., 2021) and porpoises (Jauniaux et al., 2014; Leopold et al., 2015; van Neer et al., 2020). Further, data collection protocols for seals and porpoises have been suggested in addition to decisions trees aimed at providing a guidance during decision making as well as a standardised collection of data (van Neer et al., 2020; 2021). As complementary tools, molecular methods have been suggested to detect DNA traces of a suspected predator (Heers et al., 2018; Van Bleijswijk et al., 2014) or scavenger (Heers et al., 2017) in lesions on harbour porpoises, but have also aimed at evaluating the rate of indirect mortality. Foster et al. (2019) have suggested forensic microbiology as a method to determine infections in harbour porpoises with bacteria common in grey seals such as Neisseria animaloris which potentially originate from grey seal bites often evident as scar patterns. These infections can lead to death despite the survival of a prior grey seal attack. Therefore, molecular methods such as the detection of predator DNA, as well as the detection of bacteria common in grey seals should be used as complementary tools on a regular basis during necropsies of suspicious cases. 42 | ICES SCIENTIFIC REPORTS 3:19 | ICES Current work in progress focuses on methods providing means of quantifying rates of predation by grey seals by genetically screening scat samples of grey seals for traces of harbour seal or harbour porpoise DNA using the metabarcoding technique. Results from a pilot study assessing samples from Germany show that this approach can be used to successfully study the prey spectrum utilised by grey seals including marine mammals (Elmgreen Pedersen, 2019) and has the potential to be applied on a larger spatial and temporal scale. 1.4.3 Fishery bycatch For general information on bycatch, we refer to ToR C. 1.4.3.1 Potential biological removal of seals Potential Biological Removal (PBR) methods are used to estimate the number of individual grey seals which can be “taken” through any anthropogenic means without impacting the viability of the population. PBR requires a minimum population size (Nmin), typically the 20th percentile of the mean estimate of population size is used for this purpose. Here, we briefly review the options for estimating Nmin for OSPAR regions I, II and III. It seems likely that grey seals in region I and II are part of one metapopulation; there are extensive movements between countries within and across these regions. The options are to use estimates from (1) a population dynamics model, (2) August survey counts scaled to population size (scaled August counts), (3) a mix of scaled August counts and moult counts. We recommend the latter as being most appropriate for (3) and briefly review the options below. 1. Data from the majority of region II and part of region III were encompassed into a population dynamics model for the OSPAR Interim Assessment, producing a total population estimate. This was based on (a) region-specific time-series of pup counts, and (b) a single estimate of population size pertaining to 2008 (scaled August counts). A similar exercise could be conducted to estimate the current population size in region II and III. However, the accuracy of such estimates depends on the ability of the model to emulate the underlying processes (e.g. density-dependent movements and survival) and the width of the confidence intervals are greatly influenced by data gaps in regional timeseries. Furthermore, pup production estimates are not available for all countries. 2. In the UK, grey seals are surveyed during August, and telemetry data are used to derive a scalar to raise the counts to population size. For Scottish estimates of PBR, the 20th percentile of these estimates are used as Nmin in PBR calculations (Morris et al., 2019). Although grey seal moult counts are the main survey method on the continent, in most areas grey seals are also counted during the August harbour seal surveys. However, there are some limitations associated with using a scaled August count as Nmin: (a) on the continent, August survey effort is focused on harbour seal haul outs and thus some grey seal haul outs may be missed and (b) scalars have not been calculated for the continent and preliminary analyses on UK telemetry data suggest there is regional variation in the proportion of the population hauled out during the surveys. With the exception of the UK and Ireland, most countries in regions II and III conduct grey seal moult counts. Although there is no information on what proportion of the population are hauled out, by their nature these counts represent an absolute minimum population size, and thus can be used directly as Nmin. Telemetry data suggest that, although there is clear redistribution between August and the breeding season, there is limited redistribution between August and the moult, indicating that combining scaled August counts in the UK and Ireland with moult count on the continent would not result in significant double counting. Although maximum, rather than average, moult counts can be used, caution is required when combining data across ICES | WGMME 2021 | 43 multiple survey areas to avoid potential double counting. For areas in which grey seal populations are surveyed only in the breeding season, the 20th percentile of the resulting population estimate should be used after reviewing the potential for ‘double counting’ due to redistribution between the breeding season and the rest of the year. 1.4.4 Pollution BALTIC SEA: The EU BONUS project BALTHEALTH (2016-2020) studied multilevel health impacts of anthropogenic hazardous substances on wildlife in the Baltic Sea. This Baltic Sea has previously seen large declines of marine mammal populations associated with high tissue concentrations of environmentally persistent chemicals (Bergman, 1999; Helle, 1980; Sonne et al., 2020). The project included reviews and investigations on pollutants. Although contamination with mercury has improved much over recent decades, grey seals, harbour seals, ringed seals and harbour porpoises, still have concentrations, where population effects on reproduction are probable (Dietz et al., 2021a, b). This is probably also the case for PCBs and DDTs with effects on reproduction and immune systems, although concentrations and effects are greatly reduced since the banning of these substances and the populations of seals have been recovering during recent decades (Dietz et al., 2021a; Sonne et al., 2020a). However, pollutants may still cause immunosuppression in seals and porpoises in the Baltic Sea (Sonne et al., 2020b). While the impacts of legacy contaminants such as PCBs and DDT have been reduced during recent decades, new chemicals have replaced them, and there are concerns about the levels and biomagnification potential of organophosphate esters, chlorinated paraffins, halogenated flame retardants (HFR) and perand polyfluorinated substances (PFAS) in Baltic Sea biota is lacking. An investigation of these substances at various trophic levels revealed considerable biomagnificaton potential, particularly for HFRs and PFASs (de Wit et al., 2020). There are still knowledge gaps regarding the toxicities of these emerging contaminants, particularly with regard to complex mixtures and additive effects. PCB and DDT exposure has been demonstrated to lead to morphological changes in liver cells. Schmidt et al. (2020a) found that histopathology of grey seal liver tissue (portal mononuclear cell infiltration, random mononuclear cell infiltration, lipid granulomas, hepatocellular fat vacuoles, hepatic stellate cells and mild multifocal bile duct hyperplasia accompanied by portal fibrosis were investigated). Several of these pathologies were correlated with age. Hepatic stellate cells and mild multifocal bile duct hyperplasia were correlated with adipose tissue (blubber) concentrations of PCBs, demonstrating that PCB pollution may contribute to liver pathology in marine mammals. Schmidt et al. (2020b) examined skulls of ringed seals from the Baltic Sea and Greenland using museum samples using dual-energy x-ray absorptiometry to measure bone mineral density (BMD). Skull BMD of the Baltic seals was positively correlated with the historical polychlorinated biphenyls (PCB) contamination, showing potential effects on the constitution of bones. BMD fluctuated between the three study periods with the lowest BMD found between 1897 and 1957. The highest peak of the contaminant concentration in the Gulf of Bothnia was in the second period and the BMD levels increased with increasing PCB concentrations. In porpoises from the inner Danish waters, there were indications that stressors such as parasites, noise and pollutants affect blood values of stress markers such as eosinophils and white blood cells, as there were higher levels in free-ranging porpoises than in porpoises under human care (Siebert et al., 2020a). Harbour porpoises from the inner Danish, Polish, Latvian and Baltic German waters furthermore had more severe parasitic infections compared to porpoises from Norway, Iceland and Greenland, which may also be related to immune suppression caused by 44 | ICES SCIENTIFIC REPORTS 3:19 | ICES pollutants, as may the high level of lesions caused by infections in the respiratory tract (Siebert et al., 2020b). Silva et al. (2020) modelled effects of hunting, competition, stressful life-history events, diseases and pollution on Baltic grey seal population abundance. They found that pollution, in combination with nutritional stress can contribute to effects on abundance that are delayed and only detectable long after exposure due to bioaccumulation, decreased fecundity, delayed maturation. Cervin et al. (2020) studied the Baltic Sea harbour porpoise population and investigated the effect of a possible reduction in fecundity. Subsequently, the combined effects of bycatches and reduced fecundity were investigated in terms of population growth rate and quasi-extinction risk. The Baltic harbour porpoise population is viable in the baseline scenario without anthropogenic stressors. However, even the lowest estimated bycatch level of seven individuals per year will lead to a population collapse to ≤50 animals with high probability (0.4–1.0) over the next century, assuming an intermediate or low (<73%) fecundity. Adult survival is of critical importance and mitigation of fishery impacts and reduction of anthropogenic disturbances in the identified main breeding areas were recommended in the study. FRANCE: Zanuttini et al. (2019) investigated PCBs, DDT, PBDEs, other halogenated contaminants and mercury in biopsies from coastal bottlenose dolphins from Normandy and Brittany from 2010 to 2012. They found high concentrations across all examined substances, even compared with cetacean data from other industrialized areas, and effects on reproduction, immune function and juvenile survival, as well as other parameters are probable. The population is also exposed to several other threats and pressures such as noise pollution, tourism and bycatch and the authors call for protective measures to ensure its viability. IRELAND: Schlingermann et al. (2020) shows that high levels of persistent organic pollutants occur in killer whales stranded in Ireland. The concentrations of pollutants were investigated in blubber samples from a mother–foetus pair, an adult female and an adult male killer whale stranded in Ireland between 2010 and 2017. PCBs, brominated flame retardants and organochlorine pesticides continue to be of major concern for marine apex predators such as killer whales. With this study, contaminant data for a sparsely studied region has been expanded. It also provides information regarding the rare stranding of mother–foetus killer whale pair. UNITED KINGDOM: Troisi et al. (2020) found that the concentrations of PCBs in grey and ringed seals from the Baltic, sampled between 1998 and 2002 were higher than equivalent samples of grey seals from Sable Island, Canada and Svalbard. There were significant correlations of PCB concentrations with lower concentrations of progesterone, estradiol and estrone and testosterone within several segments of the populations. This potential impact om hormone homeostasis may have effects on the reproductive health of these populations. PCBs remain a severe problem for marine mammals around western Europe (Jepson et al., 2016). Williams et al. (2020) found that due to maternal transfer seems to favour more neurotoxic PCB congeners and that in consequence, juvenile harbour porpoises are exposed to a particularly neurotoxic mixture during development of the nervous system. Thus, a simplistic correlation of total PCB exposure and effects may not be adequate to estimate risk for cetaceans. Furthermore, congener profiles also vary with sex and location. The effects of PCBs on female fertility are well known, but there also seem to effects on male reproduction. Williams et al. (2021) found that blubber PCB concentrations were associated with lower testes weights in adult male harbour porpoises from the UK in good body condition. ICES | WGMME 2021 | 45 1.4.5 Marine debris Kühn and van Franeker (2020) published a global review on all marine mammal species that have been found to interact with marine debris by either ingesting it or by getting entangled in debris. Out of 123 marine mammal species, 69 were recorded with ingested plastics and 49 as being entangled. In total, 86 marine mammal species interacted with marine debris. The authors also provide the incidence of plastic ingestion for each species separately, including all known individual records. From their results, it becomes clear that plastic ingestion is highly dependent on species groups. For example, seals seem to be less prone to plastic ingestion than cetaceans. However, different sampling methods and varying sample sizes make detailed comparisons difficult. Since the publication of this review, three new species have been detected with ingested marine debris: southern right whale (Eubalaena australis; Alzugaray et al., 2020), Indo-Pacific humpback dolphin (Sousa chinensis; Zhang et al., 2020) and marine otter (Lontra felina; Santillán et al., 2020). An increase in species accounts however, does not allow any conclusions in potential trends of plastic pollution or ingestion in marine mammals. It rather indicates increased interest by the scientific community. A review study focussing on specifically microplastics in marine mammals was recently published by Zantis et al. (2021). They provide an extensive overview on distribution, research methods, and outcomes of studies that have detected microplastics in marine mammals. An example of a recent study in the ICES area is provided by Philipp et al. (2020). They studied the abundance of microplastic in intestines and faeces of grey seal and harbour seal occurring in the German North Sea and Baltic Sea. Apart from finding plastic particles (n = 255) in ten intestine and nine faecal samples this study established a protocol for sample handling, microplastic isolation and quantification of gastrointestinal tracts and faecal samples of marine mammals with a low share of contamination. This approach helps to quantify the presence of microplastics in free-ranging marine mammals in a standardized way. No recent records of marine mammal entanglement in debris have been published in the ICES area in 2019–2020. 1.4.6 Underwater noise Popper et al. (2020) and Lucke et al. (2020) reviewed the regulatory context of underwater noise. They conclude that there is a need for far more data on which to base regulation and mitigation, as well as for deciding on future research priorities, and that this will require a process whereby regulators and researchers come together to identify and implement a strategy that links key scientific and regulatory questions. This lack of information on species distribution, abundance, habitat use and behavioural response to impulsive noise is one of the major problems identified by von Benda-Beckmann et al. (2020) in their attempt to develop a policy supporting advice on the assessment of the impact of impulsive noise on marine life in the North Sea following the method proposed by OSPAR (Merchant et al., 2018). They too recommend dedicated research targeting identified data gaps and a joint effort collating and analysing existing international spatial data. Risch et al. (2021) contest several of the points made by Popper et al. (2020) namely that the automatic assumption that animals are adversely affected by sounds, inevitably leads to regulation and mitigation of the sound source, and that mitigation actions are often taken without justification. For the former, they show that currently the focus is still on assessment and monitoring rather than prevention and mitigation (as shown by Merchant et al., 2018). For the latter, they agree that extrapolating from demonstrated harm to individuals to an assessment of population-level effects is difficult but argue that reducing the source level of a sound reduces the area of habitat affected and thus reduces impacts, both known and unknown, in many taxa, from individual to ecosystem level. 46 | ICES SCIENTIFIC REPORTS 3:19 | ICES Regulations designed to mitigate the effects of man-made sounds on marine mammal hearing specify different maximum daily sound exposure levels for impulsive and non-impulsive sounds. However, these regulations do not indicate how to quantify impulsiveness; instead, sounds are grouped by properties at the source. Martin et al. (2020) introduced a general definition for the effective quiet threshold (EQT) in marine mammals and investigated the impulsiveness of human and natural sounds whose per-minute sound levels exceeded the proposed EQT. They recommend using the 1-minute auditory frequency weighted kurtosis as the best metric for quantifying impulsiveness with an auditory-frequency weighted kurtosis threshold of 40 as an initial limit for a sound being “fully” impulsive when considering the effects of sound on marine mammal hearing. The kurtosis of impact pile driving and seismic survey sounds are always impulsive when their sound levels are above EQT, and therefore the transition from impulsive to non-impulsive pulse characteristics does not need to be factored into regulations for protecting marine mammals from impulsive sound sources. Sounds from vessels are normally considered non-impulsive; however, 66% of vessels analysed were impulsive when weighted for very-high frequency mammal hearing. Operational offshore wind turbines are increasingly abundant sources of underwater low frequency noise. Available measurements of underwater noise from different wind turbines during operation show that source levels are at least 10–20 dB lower than ship noise in the same frequency range. However, given the rapid increase in the number and size of offshore windfarms, the cumulative contribution from the many operational turbines may be considerable - under very low ambient noise conditions - and should be included in assessments for maritime spatial planning purposes as well and environmental impact assessments of individual projects (Tougaard et al., 2020). Between 2008 and 2020, the number of offshore wind turbines in the North Sea has almost tenfolded from ~500 to over 4000 turbines, and the capacity has grown from 1 GW to a bit less than 20 GW. Driven by the necessity to further switch to green energy and the lately negotiated European Green Deal, further developments of wind and other renewable energy sources are being planned, growing to a capacity of 48GW by 2030, with the long-term aim to produce the 180 GW needed to decarbonise the power sector of the North Sea countries by 2045. When this target is reached, a significant portion of the North Sea will be occupied by windfarms. These ambitious EU CO2 reduction targets will also stimulate other forms of marine energy production and construction of new infrastructures, likely interfering also with MPAs, which is already discernible today. Parallel to this, plans are made to further develop food production (fisheries and aquaculture), marine traffic and the decommissioning of oil and gas infrastructure. This results in a high pressure on marine spatial planning, trying to facilitate at relatively short notice the different stakeholders while maintaining a healthy marine ecosystem. Though possibly at a slower pace, other ICES areas (for example the Baltic Sea) face similar challenges in the near future. While these plans may entail profound large-scale changes of the habitat of a large sea area, investigations and assessments hitherto have only been made at much smaller scales. In relation to the individual activities, environmental impact assessments (EIAs) on marine mammals are typically carried out aiming at recording local changes, i.e. presence, activity and habitat use in or near the construction area and concentrating on the effects of construction sound, which has been identified as a major direct impact (reported in WGMME reports). Parallel to this, efforts are made to model and map marine mammal distribution and estimate possible cumulative effects. However, there is a discrepancy in timing between the pace at which plans are being made for future development of the marine areas, and the knowledge available to avoid effects on marine mammals and other wildlife at a population level. In order to provide information for the future spatial plans, an understanding is needed on effects of activities on a longer term and ICES | WGMME 2021 | 47 larger spatial scale than the relatively short term and small scales that have been studied until now. Although there are considerable challenges in doing so, efforts should be made to evaluate effects of current and future pressures from offshore constructions and their maintenance at a population level. This includes studying changes in habitat available to marine mammals that have occurred during recent decades in places like the German Bight or along the UK coasts following the construction of large windfarms. Such studies should include linking changes in population size and distribution to the human activities and investigating plausible mechanisms that might impact population dynamics so anthropogenic pressures can be discerned from “natural” pressures such as density-dependence or interspecific competition. BELGIUM: After ten years of intermittent pile-driving activities in the first offshore renewable energy zone in Belgian waters, the last turbine foundation was hammered in the seafloor on 2 January 2020. These extra-large steel monopiles with a diameter of 7.4 and 8 m, were piled using large hydraulic hammers of 3000 and 4000 kJ, respectively (Norro, 2020). The associated excessive sound levels were reduced using a double big bubble curtain (DBBC) and in situ measurements of underwater sound generated showed zero to peak sound levels ranging from 183 to 193 dB re 1 μ Pa when normalised to a distance of 750 m from the source. This represented an estimated zero to peak sound level reduction of 12-20 dB re 1 μPa. The variability in efficiency of sound level reduction may be explained by the technical set-up of the DBBC but also by environmental conditions like tidal currents, which should receive extra attention while designing the DBBC as to optimise sound reduction. Norro (2020) further detected the efficiency of sound level reduction to be higher for frequencies above 300 Hz while mainly lower frequency sounds are emitted during pile driving. GERMANY: Underwater noise was recorded during anchor pipe vibration embedment operations in the Wadden Sea (Baltzer et al., 2020). The recorded vibration embedment noise was a continuous sound with durations of 2–55 seconds, with most energy below 1 kHz and peak frequencies around 900 Hz. Background noise level at a distance of approximately 1 km increased around 13 dB at frequencies between 800 and 1000 Hz. The estimated sound exposure level (SEL) of the source was 148.2 dB re 1 μPa2s and the median SEL ranged from 120 to 99 dB re 1 μPa2s at distances between 394 and 2288 m, respectively. The detected anchor pipe vibration embedment noise might exert a behavioural reaction on a local scale with marine mammals affected by the construction operations up to a distance of 375 m. ESTONIA: A pilot study of ringed seal diving behaviour at a regular island ferry line using telemetry, AIS data and underwater noise measurements was performed in 2019 (Prawirasasra et al., 2019). Shorter dive duration and dive depth were detected after exposure to 107 dB re 1 μPa, but no change was detected in trajectory or velocity. Behaviour reaction occurs in the close proximity (< 500 m) to the source. Given the relatively low speeds, relatively moderate source levels and regularity of the ferry traffic over decades in the area, habituation of seals to acoustic environments and ferry traffic was suggested. NETHERLANDS: As part of project on the frequency-dependent susceptibility to noise-induced temporary hearing threshold shift (TTS) in harbour seals (Phoca vitulina), two seals were exposed to one-sixth-octave noise bands (NBs) centred at 0.5, 1, 2, 32 and 40 kHz 1 at several sound exposure levels (SELs, in dB re 1μPa²s) (Kastelein et al., 2020a, b and c). The highest TTSs (>45 dB) occurred at 45 kHz, one-third of an octave above the fatiguing sound’s center frequency (SEL ~191 dB re 1 μPa²s) and recovery took four days. In most other cases, recovery was within one hour. From 0.5 to 2.8 kHz, the lower the center frequency of the fatiguing sound, the higher the SEL required to cause the same TTS. The seals have a similar susceptibility to TTS from 4 to 40 kHz. 48 | ICES SCIENTIFIC REPORTS 3:19 | ICES PORTUGAL: The Azores archipelago is an important cetacean hotspot, registering a very relevant resident and migratory population. As part of a study to evaluate and quantify the direct impact of underwater noise from shipping on this cetacean population, Soares et al. (2020) developed a numerical model that provided satisfactory predictions of the underwater noise in the area which could be a useful risk assessment tool for cetaceans in Azores archipelago. UNITED KINGDOM: There are increasing concerns about impacts of anthropogenic noise pollution on marine mammals at sea, given spatio-temporal overlap between animals and noise sources (principally shipping and pile-driving associated with windfarm construction). However, accurate information on at-sea exposure is still often lacking. Farcas et al. (2020) reported on new efforts to map levels of underwater noise pollution, which is an essential first step for successful management. The authors developed a computational model of underwater noise levels in the northeast Atlantic generated by commercial shipping, based on Automatic Identification System (AIS) data, wind speed data, bathymetry, sound speed, seabed reflectivity and acoustic frequencies. Model predictions were subsequently validated using concurrent field measurements of ambient noise levels from four monitoring stations off the east coast of Scotland, deployed as part of the Marine Scotland East Coast Marine Mammal Acoustic Study (ECOMMAS). The model performed well, with model predictions for median sound levels for third-octave frequency bands within 125 Hz–5 kHz falling within ±3 dB of 93% of observed values. High predicted sound levels (in excess of 120 dB re 1μPa and 20 dB above modelled background levels) were predicted in the English Channel, Norwegian Trench, and in the vicinity of major ports and offshore hydrocarbon infrastructure. Higher levels of shipping noise were predicted in summer, potentially due to a combination of more shipping activity and less wind. Predictive noise maps such as those produced during this study clearly have an important role in managing impacts of shipping noise on acoustically sensitive species such as marine mammals. Trigg et al. (2020) reported on efforts to predict exposure of adult and pup grey seals (Halichoerus grypus) travelling in the Celtic Sea and English Channel to shipping noise. The authors used data from GPS telemetry tags for tracking seals at sea in combination with Automatic Identification System (AIS) data to determine the location of ships at sea in relation to the grey seal tracks. Exposure of seals to shipping noise was then evaluated based on modelled ambient received noise levels, based on estimated ship source levels and a three-dimensional acoustic propagation model (RAMSurf). Three-dimensional exposure of grey seals to shipping noise ranged from 124 to 170 dB re 1 μPa2·s in 24-h when weighted using the underwater frequency weighting function for pinnipeds proposed by Southall et al. (2007). These predicted exposure levels did not exceed thresholds for temporary threshold shifts, and were driven by numbers of ships, ship’s noise source level, the distance between seals and ships, and the at-sea behaviour of the seals. Similarly, Whyte et al. (2020) sought to investigate effects of pile driving sounds (associated with windfarm construction) on harbour seals (Phoca vitulina) tracked using GPS telemetry tags off southeast England. Seal positions, diving and movement data were evaluated against estimated single-strike sound exposure levels (SELss) using the Aquarius pile driving model. Model sensitivities were tested using different weighting functions and thresholds for predicting auditory damage, evaluating acoustic exposure of each seal across space and time, and exploring effects on at-sea seal density. Predicted seal density significantly decreased within 25 km or above SELss (averaged across depths and pile installations) of 145 dB re 1 μPa2·s. The authors reported notable differences in numbers of seals predicted to suffer auditory damage, depending on which weighting functions and thresholds were used. More broadly, the authors illustrated clearly how the choice of analytical method may result in divergent conclusions about the severity of acoustic impacts on at-sea seal distribution, and thereby influence potential management decision-making. ICES | WGMME 2021 | 49 UK mitigation guidance to reduce acoustic impacts of pile driving associated with windfarm construction currently require use of Marine Mammal Observers (MMOs; JNCC, 2010). The use of Acoustic Deterrent Devices (ADDs), which temporarily causes animals to avoid the area, was recently proposed as an alternative approach to ensure animals are not exposed to sound levels that could lead to injury or mortality. Thompson et al. (2020) investigated questions surrounding this approach, with particular focus on measuring received noise levels in relation to varying hammer energy during piling, undertaking ADD playback experiments prior to piling to evaluate harbour porpoise responses, and to characterise ADD source levels. Data were collected in the Moray Firth, Scotland, during the construction of the BOWL windfarm in 2017. The study highlighted a surprising inverse relationship between received noise levels and hammer energy. Moreover, long-standing assumptions of constant, low proportions of hammer energy converted to acoustic energy (known as conversion factors) during piling were found to be incorrect, with conversion factors varying by an order of magnitude (between 1 and 10%, rather than the ~0.5% as previously assumed). Porpoises responded strongly to the ADD signal over large distances (>10 km), pointing to a need for optimisation of ADD playback duration to avoid unnecessary far-field disturbance while still ensuring nearfield avoidance. Risch et al. (2020) measured underwater sound emitted by an operational, 1.5 MW three-bladed horizontal-axis tidal turbine (Atlantis AR1500), using autonomous passive acoustic recording systems suspended below freely moving Lagrangian drifters to reduce flow noise. Results indicated that, under conditions of low wind (≤2 Bft) and moderate tidal flow (1–4 m s-1), low frequency underwater sound (100–1000 Hz) produced by the turbine was clearly detectable at distances of at least 2300 m, although this range would be reduced under higher wind conditions. However, detectability of the device under higher tidal flow conditions was expected to increase, potentially reducing risk of marine mammals colliding with the rotating turbine. Working on the same site, Gillespie et al. (2020) described a new system to acoustically track vocalising marine mammals in 3D around anthropogenic structures. The system evaluated 3D positions of vocalising marine mammals based on time of arrival difference (TOAD), using an array of 12 hydrophones and supporting software. Over 322 days of data collection around a tidal turbine in the Pentland Firth, northern Scotland (the MeyGen project), >700 porpoise events and 26 dolphin events containing ≥10 clicks were identified. Daily encounter rates of both species varied seasonally, with rates increasing in autumn and winter. 3D localisation at approximately 2 m accuracy proved possible with ranges of ~30 m. This system was designed to assist risk assessment of potentially hazardous interactions between marine mammals and underwater structures, such as tidal turbines, where understanding of small-scale movements is often lacking at present. Unexploded ordnance (UXO) on the seabed can delay or impede marine activities such as construction of offshore windfarms. Once discovered, such UXOs are often disposed of by controlled on-site detonation, but the resulting loud acoustic pulses pose a hazard to marine mammals and other acoustically sensitive species and can cause damage to the surrounding seabed. Robinson et al. (2020) compared the sound characteristics of standard explosive ordnance disposal with a technique known as deflagration, where the UXO shell is penetrated but not detonated, at which point the explosive material inside the UXO reacts with a rapid burn rather than an explosive chain reaction. Both methods were compared experimentally by controlled detonation of standardised explosives in a freshwater test site situated in an abandoned quarry, measuring peak sound pressure (in MPa and dB re 1 μPa) and sound exposure level (SEL, in dB re 1 μPa2s). Results indicate that the deflagration approach produces much lower amplitude of peak sound pressure than high-order detonations by a factor of just over 10. Deflagration appears to offer a suitable alternative for controlled disposal of at least a subset of UXOs resulting in much reduced acoustic exposure of marine species and disturbance of the seabed. 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Observatoire Pelagis (UMS 3462, La Rochelle Université / CNRS) and Parc naturel marin de l'Estuaire de la Gironde et de la mer des Pertuis (Office Français de la Biodiversité): 47 pp. van Neer, A., Gross, S., Kesselring, T., Grilo, M. L., Ludes-Wehrmeister, E., Roncon, G., and Siebert, U. 2020. Assessing harbour porpoise carcasses potentially subjected to grey seal predation. Scientific Reports, 10(16345). https://doi.org/10.1038/s41598-020-73258-y. van Neer, A., Gross, S., Kesselring, T., Grilo, M., Ludes-Wehrmeister, E., Roncon, G., and Siebert, U. 2021. Assessing seal carcasses potentially subjected to grey seal predation. Scientific Reports, 11(694). https://doi.org/10.1038/s41598-020-80737-9. van Neer, A., Gross, S., Kesselring, T., Wohlsein, P., Leitzen, E., and Siebert, U. 2019. Behavioural and pathological insights into a case of active cannibalism by a grey seal (Halichoerus grypus) on Helgoland, Germany. Journal of Sea Research, 148–149, 12–16. https://doi.org/10.1016/j.seares.2019.03.004. van Neer, A., Jensen, L. F., and Siebert, U. 2015. Grey seal (Halichoerus grypus) predation on harbour seals (Phoca vitulina) on the island of Helgoland, Germany. Journal of Sea Research, 97, 1–4. https://doi.org/10.1016/j.seares.2014.11.006. Vanhatalo, J., Vetemaa, M., Herrero, A., Aho, T. and Tiilikainen, R. 2014. Bycatch of grey seals (Halichoerus grypus) in Baltic Fisheries – A Bayesian analysis of interview survey. PLoS ONE 9: e113836. Virgili, A., Laran, S., Authier, M., Doremus, G., Van Canneyt, O. and Spitz, J. 2020. Prospective modelling of operational offshore windfarms on the distribution of marine megafauna in the southern North Sea. bioRxiv, 2020.2012.2016.423009. (https://www.biorxiv.org/content/10.1101/2020.12.16.423009v1). Von Benda-Beckmann, S., Geelhoed, S.C.V., Kinneging, N., van Kuijk, B., Scheidat, M. and Versteeg, S. 2020. Assessment methodology for impulse noise: A case study on three species in the North Sea. Arnhem, Arcadis. IJsseldijk, L.L., ten Doeschate, M.T.L., Brownlow, A., Davison, N.J. Deaville, R., Galatius, A., Gilles, A., Haelters, J., Jepson, P.D., Keijl, G.O., Kinze, C.C., Olsen, M.T., Siebert, U., Thøstesen, C.B., van den Broek, J., Gröne, A. and Heesterbeek, H. 2020. Spatiotemporal mortality and demographic trends in a small cetacean: Strandings to inform conservation management. Biological Conservation 249: 108733. https://doi.org/10.1016/j.biocon.2020.108733. 58 | ICES SCIENTIFIC REPORTS 3:19 | ICES IJsseldijk, L.L., van Schalkwijk, L., van den Berg, A., ten Doeschate, M.T., Everaartsm E., Keijlm G.O., Kuijpers, N., Bravo Rebolledo, E.L., Veraa, S. and Kik, M.J. 2020. Fatal attraction: The death of a solitarysociable bottlenose dolphin due to anthropogenic trauma in the Netherlands. Lutra 63: 17–32. Waggitt, J.J., Evans, P.G.H., Andrade, J., Banks, A.N., Boisseau, O., Bolton, M., Bradbury, G. et al. 2020. Distribution maps of cetacean and seabird populations in the North-East Atlantic. J Appl Ecol. 57: 253– 269. https://doi.org/10.1111/1365-2664.13525. Whyte, K.F., Russell, D.J., Sparling, C.E., Binnerts, B. and Hastie, G.D. 2020. Estimating the effects of pile driving sounds on seals: Pitfalls and possibilities. The Journal of the Acoustical Society of America 147(6): 3948–3958. Wood, S.A., Murray, K.T., Josephson, E. and Gilbert, J. 2019. Rates of increase in gray seal (Halichoerus grypus atlantica) pupping at recolonized sites in the United States, 1988–2019. Journal of Mammalogy, XX(X):1– 8. Zantis, LJ., Carroll, E.L., Nelms, S.E. and Bosker, T. 2021. Marine mammals and microplastics: A systematic review and call for standardisation. Environmental Pollution 269: 116142 doi https://doi.org/10.1016/j.envpol.2020.116142. Zhang, X., Luo, D., Yu, R-Q., Xie, Z., He, L. and Wu, Y. 2020. Microplastics in the endangered Indo-Pacific humpback dolphins (Sousa chinensis) from the Pearl River Estuary, China. Environmental Pollution: 116057 doi https://doi.org/10.1016/j.envpol.2020.116057. Øigård, T.A., Frie. A.K., Nilssen, K.T. and Hammill, M.O. 2012. Modelling the abundance of grey seals (Halichoerus grypus) along the Norwegian coast. ICES Journal of Marine Science, 69: 1446–1447. doi:10.1093/icesjms/fsq103. ICES | WGMME 2021 | 59 2 ToR B: Review foraging areas and estimate consumption by harbour seal, grey seal and harbour porpoise in the North Sea case study area The aim of ToR B is to review species-specific foraging distributions (considering horizontal and vertical dimensions depending on data availability) and to estimate consumption by marine mammal species representative in case study areas. ToR B has been agreed between WGMME and WGBIODIV to support WGBIODIV’s ToR “Investigate mechanisms linking trophic guilds under contrasting levels of pressure and/or primary production in case study areas”. This year, the WG focussed on diet and prey consumption and did not consider foraging distributions. However, some new information on distribution is included under ToR A. 2.1 Outline WGBIODIV has requested diet information: 1. For prey guild models. The request is for comprehensive information on prey consumed by marine mammals in the North Atlantic, with an indication of the importance of each prey in the diet. 2. For ECOPATH modelling of the North Sea, estimates of North Sea predator diets for the year 1991 (the baseline year of the models), with a focus on fish species or groups that are included in the ECOPATH modelling in progress for the North Sea. The request is for estimates of diet composition based on prey biomass or consumption rates. This information will be used to parameterise the baseline ECOPATH model to estimate predator preferences for different prey. Marine mammal diets, especially pinnipeds, have mostly been estimated from hard prey remains recovered from gastro-intestinal tracts (GIT, usually stomachs) or faeces (scats). DNA-based analysis can also provide information on diet, as can the analysis of fatty acids and stable isotopes. These techniques make a range of assumptions about the sample data and the analytical method; see reviews in Tollit et al. (2010) and Bowen and Iverson (2013). A number of aspects of stomach/scat analysis are important to consider in the context of providing robust estimates of diet composition. These include: 1. Samples may not be representative of the population. For cetaceans, stomachs are usually taken from stranded or bycaught animals (less commonly from animals killed directly), neither of which is likely to provide a representative sample of diet. For seals, scats are usually collected from haul-out sites on land, which may over-emphasize prey taken closer to shore. Information on prey distribution, predator foraging distribution and the passage time of prey remains through the predator GIT can be used to assess sample representativeness. 2. Information about the individual predator (size, sex, reproductive status, health status) can be associated with stomach samples but is limited to sex (through DNA analysis) for scat samples. DNA analysis of scats may also be needed to confirm predator species (e.g. Wilson, 2014). 3. Some prey may not have useful recoverable hard remains (especially fish otoliths and cephalopod beaks), so estimates of diet composition based on hard parts will miss prey 60 | ICES SCIENTIFIC REPORTS 3:19 | ICES species that do not leave such remains. The heads of large fish prey may not always be consumed by seals, potentially creating a bias in the diet towards smaller fish. The extent of this bias is unknown but, for example, otoliths from large fish are frequently found in grey seal scats (e.g. Hammond and Wilson 2016; Wilson et al., 2019). 4. In analysis of hard prey remains, some otoliths may be too digested to be assigned to species (particularly otoliths). 5. Hard prey remains will be partially (and maybe completely) digested in the GIT of the predator. These digestion rates are predator and prey species-specific (e.g. Grellier and Hammond, 2006; Wilson et al., 2017) and need to be incorporated in analysis to avoid/minimise bias. Stomach and scat samples will be affected differently. 6. All prey remains, including soft tissue, can be examined in stomachs but it is more challenging to quantify diet when including all this material. 7. Processing stomach/scats and identifying hard prey remains is time consuming, and personnel costs may be high to analyse a large number of samples. 8. A small amount of diet information relevant to ToR b is derived from DNA-based analysis. There are also multiple assumptions/challenges with using this method, including in providing quantitative diet estimates. Nevertheless, DNA-based analysis can enhance hard prey remains analysis by identifying prey species missed by hard part analysis (e.g. Tollit et al., 2009; Méheust et al., 2015). Recent developments in DNA metabarcoding have been used to investigate diet in Bryde’s whales (Carroll et al., 2019). Sources of published and unpublished diet information for marine mammal species in the North Sea and adjacent waters (primarily grey seal, harbour seal, harbour porpoise and minke whale) are listed in Table 2.1. These and potentially other data sources will need to be accessed, processed and/or analysed to provide inputs for prey guild and ECOPATH modelling. The WG was unable to generate robust estimates of diet composition for WGBIODIV during the meeting. This will require combining data from different studies and considerable time for data processing and analysis. Instead, the WG considered a number of example case studies as illustrations of the nature of the available data and information, and proposed an outline methodology for combining and analysing data. ICES | WGMME 2021 | 61 Table 2.5. Information on diet (a), abundance and distribution (b) of harbour porpoise, grey seal and harbour seal in the North Sea, as well as Skagerrak, Kattegat and the Limfjord. country species timeline area spatio-temporal resolution availability published contact Netherlands Harbour porpoise 1990–present Dutch coastline; North Sea and Wadden Sea Season, region Yes, stomach contents (n > 500) Leopold, 2015 Mardik Leopold Grey seal 1990–present unknown Not yet; not all scat samples have been analysed. Specific study and budget would speed up the process. No Sophie Brasseur Harbour seal 1980–present No Sophie Brasseur 2002–2009 Dutch Wadden Sea unknown Not yet, (n =103) scat samples Aarts et al., 2019 Sophie Brasseur Others Unknown Mardik Leopold United Kingdom [Scotland, England] Harbour porpoise Unknown 1992–2003 1989–1994 1989–1996 UK coastline Scotland, North Sea and Atlantic UK waters Scotland, Denmark, Scotland, Spain Unknown Region, season Unknown Region Not yet, but currently both datasets on stomach contents are being finalised Unknown, stomach content (n=188) Unknown, stomach content (n=100) Unknown, stomach content (n=198) No Santos et al., 2004 Martin 1996 Santos 1998 Graham Pierce, Simon Northridge Graham Pierce Graham Pierce Grey seal 1985, 2002, 2010–2011 1992 UK coastline; North Sea and Western Scotland Moray Firth, North Sea Annual, season, region No Yes, scat samples Unknown, scat samples (n =94), ongoing sampling? Wilson et al., 2019; Hammond and Wilson, 2016 Thompson et al., 1996 Philip Hammond Paul Thompson 62 | ICES SCIENTIFIC REPORTS 3:19 | ICES country species timeline area spatio-temporal resolution availability published contact 2005–2009; 2011–2013 2009–2013 1972–2008 Scotland, North Sea Southwest and southeast Ireland, Atlantic, Irish Sea UK Coastline, North Sea No Annual, season decadal Unknown, (n=30), digestive track and DNA. Shot seal from salmon net fisheries Unknown, scat samples (n>494) Unknown, Stable isotopes (n =69) Harris et al., 2014 Gosch, 2017 Hanson et al., 2017 Simon Northridge Harbour seal 2010–2012 2005–2009; 2011–2013 1995–2000 1998–2003 1988–1989; 1992; 2000 2006–2007 1993--1994 UK coastline; North Sea and Western Scotland Scotland, North Sea Northeast Ireland, Irish Sea St Andrews Bay and Firth of Tay, North Sea Moray Firth, North Sea Southwest Ireland, Atlantic West of Scotland, Atlantic Annual, season, region No Annual Annual, season, region Annual No Annual, month, region Yes, scats Unknown, (n=6), digestive track and DNA. Shot seal from salmon net fisheries Unknown, scats (n = 200) Unknown, scats (n =749) Unknown, scats (n=40,308,214), ongoing sampling? Unknown, scats (n=102) fatty acids (n=13) Unknown, scats (n > 140) Wilson et al., 2019; Hammond and Wilson 2016; Wilson 2014 Harris et al., 2014 Wilson et al., 2002 Sharples et al., 2009 Thompson et al 1991;1996 Middlemas et al., 2006 Kavanagh et al., 2010 Pierce and Santos, 2003 Philip Hammond; Lindsey Wilson Simon Northridge Graham Pierce Philip Hammond Paul Thompson Graham Pierce Graham Pierce ICES | WGMME 2021 | 63 country species timeline area spatio-temporal resolution availability published contact 1995–1996 1990–1992 Shetland Southwest England, North Sea Month Annual Unknown, Scats (n>733) Unknown, Scats (n=708) Brown and Pierce 1997;1998 Hall and Hammond, 1998 Philip Hammond Philip Hammond others Scottish coastline Maybe No Stranding’s network Belgium Harbour porpoise 1997–2018 Belgian coastline Season Not yet, (n =180) stomach content Haelters et al., 2012; MSc thesis Lambert 2020. Available upon request. Jan Haelters Grey seal Yes, historical data. More recent data still needs to be processed (n ~ 100). Harbour seal Seabirds Erik Stienen Germany Harbour porpoise 1982–1990; 1992–1993 German North Sea and Baltic coastline Yes, historical data; More recent data still needs to be processed. Lick 1991; Benke et al., 1998 Anita Gilles, Ursula Siebert (SchleswigHolstein); 1994–2006 German North Sea and Baltic Sea Time period, season, Unknown, (n = 129; of these n=53 Baltic Sea, n=62 North Sea) stomach content and QFASA; more recent data analysed at the moment Gilles et al., 2008; Gilles 2009 1980–2011 western Baltic Sea Annual, season Unknown, (n = 339) stomach content, estimated consumption Andreasen et al., 2017 Grey seal 2000–2006 No (n=15) QFASA; more recent data analysed at the moment Gilles et al., 2008 64 | ICES SCIENTIFIC REPORTS 3:19 | ICES country species timeline area spatio-temporal resolution availability published contact Harbour seal 1994–2007 German North Sea and Baltic Sea No (n=20) stomach content; (n=80) QFASA; more recent data analysed at the moment Gilles et al., 2008 Harald Benke, Michael Dähne (MecklenburgWestern Pomerania) 1981–1984; 1975–1981 Wadden Sea, SchleswigHolstein No; analysed in two time periods Sievers, 1989; Behrends 1985 2012–2014 Month Unknown, stable isotope (n =23); (n =33) de la Vega et al., 2016; de la Vega et al., 2018 Denmark Harbour porpoise 1987–2000; 2009–2010 1980–2011 The Sound, Kattegat, Baltic Sea Western Baltic Sea Season Annual, season Unknown, (n = 53) stomach content No, (n = 339) stomach content, estimated consumption Sveegaard et al., 2012; Andreasen et al, 2017 Signe Sveegaard Grey seal 2005–2007, 2013 Kattegat No Yes. Review of previous studies in Skagerrak, Kattegat, the Limfjord and the Baltic Sea. New samples from Kattegat (scats, n=32). Scharff-Olsen et al., 2018 Anders Galatius, Morten Tange Olsen Harbour seal 1990 1997–1998 2005–2007 Limfjord Kattegat No Annual, season Annual, season Unknown. Scats (n=32) Unknown. Scats (n=106) Review of previous studies in Skagerrak, Kattegat, the Limfjord and the Baltic Sea. New samples from Kattegat (scats, n=43) Friis et al., 1994, Andersen et al., 2007 Scharff-Olsen et al,. 2018 Anders Galatius, Morten Tange Olsen ICES | WGMME 2021 | 65 country species timeline area spatio-temporal resolution availability published contact others France Harbour porpoise 1990–present 2004–2011 French and Belgium coast, North Sea Brittany, France No No Partially; many samples need to be analysed. Stomach content (n=14), stable isotope and fatty acid (n=52) Unknown, digestive tract (n=7) Mahfouz et al., 2017 Méheust et al., 2015 Jérôme Spitz Grey seal 1998–2000 2004–2011 Brittany, France No Unknown, Scat (n =145), digestive tract (n =14), fatty acid Unknown, digestive tract (n=11) Ridoux et al., 2007 Méheust et al., 2015 Harbour seal 2000–2004 2002–2011 Normandy, France France, English Channel Annual No Unknown, scats (n=121) Unknown, scats (n=91) Spitz et al., 2010; Spitz et al., 2015 Others (Common dolphin, Striped dolphin, Bottlenose dolphin, Other cetaceans) Meynier et al., 2008; Spitz et al., 2006a; Spitz et al., 2006b; Louis et al., 2014; Spitz et al., 2011 Sweden Harbour porpoise 2007–2020 1989–1996 Kattegat, Skagerrak and the Baltic Kattegat and Skagerrak No Not yet, stomach contents (also some DNA samples are being processed) Yes, stomach content (n=112) No Börjesson et al., 2003 Anna Roos Patrik Börjesson 72 | ICES SCIENTIFIC REPORTS 3:19 | ICES 2.2.2 Harbour seal diet in the Kattegat–Skagerrak area Assessments of the diet of harbour seals in the Kattegat–Skagerrak area date back to the late 1970s. Thereafter, additional studies are available from the 1980s (Kattegat, Skagerrak), 1990s (Skagerrak) and 2000s (Kattegat, Skagerrak). The most extensive studies have been based on scat samples collected during several months in the Skagerrak in the 1970s, 1980s and 1990s, enabling assessments of interseasonal prey preferences as well as long-term dietary changes (Härkönen, 1987; Härkönen and Heide-Jørgensen, 1991; Olsen and Bjørge, 1995). Later studies from the Skagerrak, are more limited in sample sizes (Strömberg et al., 2012; Sørlie et al., 2020). The diet of harbour seals in the Kattegat has not been studied to the same extent as in the Skagerrak, and available information is based on fewer samples and more limited seasonal coverage (Härkönen, 1987; Härkönen, 1988; Strömberg et al., 2012; Lundström et al., 2017). Previous studies from the Kattegat-Skagerrak area are typically based on collection of samples from a limited area and regional variations in diet (e.g. within the Skagerrak) are poorly known. However, the more recent study by Sørlie et al. (2020) presents area-specific variation in diet within the Skagerrak. Table 4 provides a summary of these studies. The most important prey were species belonging to the families Gadidae, Pleuronectidae, Clupeidae and Ammodytidae, with some variation between studies. Gadidae species were more common in the Skagerrak and frequently occurring species were Atlantic cod, Norway pout, poor cod, blue whiting and whiting. Pleuronectidae species, on the other hand, were more common in the Kattegat, dominated by common dab, European plaice and European flounder. Harbour seal diet studies in areas adjacent to the Kattegat-Skagerrak area have also been conducted, in the Limfjord and along the Norwegian North Sea coast (Friis et al., 1994; Olsen and Bjørge, 1995; Bjørge et al., 2002; Østbøll, 2005; Andersen et al., 2007). Due to the absence of recent diet data from the Kattegat-Skagerrak area, diet samples, both scats and digestive tracts from hunted seals, are currently collected to obtain updated results on the harbour seal diet, including spatial and temporal variability (K. Lundström, SLU). ICES | WGMME 2021 | 73 Table 2.8. Harbour seal diet studies from the Kattegat–Skagerrak area. Area Year Month Sample type n samples n otoliths Reference Kattegat 1980 Jul–Sep Scats 63 Härkönen, 1987 Skagerrak 1977–1979 Jan–Dec Scats 314 8572 Härkönen, 1987 Kattegat 1980 May–Sep Scats 71 2187 Härkönen, 1988 Skagerrak 1980 June Scats 32 612 Härkönen, 1988 Skagerrak 1984 Stomachs 29 515 Aspholm et al., 1995 Skagerrak 1989 Scats 16 132 Aspholm et al., 1995 Skagerrak 1989 Jul–Sep Scats na 6797 Härkönen and HeideJørgensen, 1991 Skagerrak 1990–1991 Apr–Nov Scats 194 3039 Olsen and Bjørge, 1995 Kattegat 2005–2007 Apr–Oct Scats 43 NA Scharff-Olsen et al., 2018 Kattegat 2009–2011 Digestive tracts 52 4151 Strömberg et al., 2012, Lundström et al., 2017 Skagerrak 2009–2011 Digestive tracts 8 4151 Strömberg et al., 2012 Skagerrak 2015–2016 Jun–Aug Scats 121 757 Sørlie et al., 2020 Kattegat 2019 Seasonal Digestive tracts, scats Ongoing K. Lundström, SLU Skagerrak 2.2.3 Minke whale diet in the North Sea Stomach analyses of 37 minke whales in the North Sea in 2001–2003 showed sandeels (Ammodytidae spp.) to be the most important prey, occurring in 62% of the stomachs and contributing 57% of the biomass by weight. Mackerel Scomber scombrus, herring and Mueller’s pearlside, Maurolicus muelleri contributed approximately 30%, 6% and 5%, respectively. Haddock was not present in the diet in 2001 but contributed 2.4% in 2003. The eastern part of the North Sea is an important area for sandeel, and this was reflected in minke whale diet; 87.5% of the whales had fed more or less exclusively on this prey item in this area. In 2001, the dietary contribution of sandeel was larger than in 2003. The lower contribution of sandeel in 2003 could be a result of poor recruitment during the period before the whales were taken, perhaps due to overfishing. Sandeel landings (350 000 t annually) in 1997 and 1998 were much higher than in 1999 (188 000 t) and 2000 (119 000 t). Sandeels in minke whale diet were, on average, much larger in 2001 than in 2003. The large sandeels present in the diet in 2001 were largely absent in 2003, confirming the poor sandeel year classes of previous years (Windsland et al., 2007). 2.2.4 Diet studies in German waters Within the project BioWeb (2020–2023) diet studies for harbour seal, grey seal and harbour porpoise in the German North Sea, using metabarcoding on scats as well as traditional hard-part 74 | ICES SCIENTIFIC REPORTS 3:19 | ICES analyses and stable isotopes, will be conducted (https://www.senckenberg.de/en/bioweb/#content-0003_2). The first outcomes of this project will be presented at WGMME 2022. 2.3 Methodology for generating diet information for WGBIODIV 2.3.1 Estimates for prey guild modelling To facilitate the cluster analysis used for the prey guild work, diet data/estimates have been requested, ideally including all prey identified, prey count and prey mass, individual predator age group, mass and length, and with date/time latitude/longitude coordinates. As indicated above, not all prey of a predator may be identified and other assumptions regarding potential biases in biomass estimates and relative importance in samples may not be met. Regarding information on individual predator age group, mass and length, as noted above, this can be obtained from GIT (stomach) samples or stranded, bycaught or directly killed animals, but not for scats, unless sex has been determined using DNA analysis. 2.3.1.1 Geographical and temporal distribution Most diet data are not associated with a specific time or location. For example, consumption of prey represented in seal scats from haul-out sites and the stomachs of stranded animals will typically have taken place days, or longer, prior to collection and in an unknown location. Accurate time/location is known only for animals killed in whaling operations, and for some bycaught animals. The spatio-temporal resolution of diet information (lists of prey species and/or diet estimates) that could be provided to inform the prey guild modelling, will depend on the data available. Such information could be provided for separate diet studies, or the results of existing studies could be combined (see below). To estimate predator diets that are appropriate for a particular time and area, with appropriate measures of uncertainty, data from sporadic sampling may need to be processed substantially. In this context, the WG noted the following points: • For cetacean species which can access wide areas (e.g. the North Sea), it may be most appropriate to aggregate all the mostly sparse data over the entire North Sea, unless regional differences in diet have been shown to exist. The appropriate time interval will depend on the availability of data; it may also be appropriate to aggregate over the whole period for which there are data, unless seasonal differences or time trends are apparent. If information is available on variation in diet by age class, for example for juvenile and adult harbour porpoise, this could be provided. The sparseness of cetacean diet data, in particular, means that estimates will be uncertain. That uncertainty may be difficult to quantify. • Diet data for cetaceans are most extensive for harbour porpoise. They are still quite sparse, but it may be possible to estimate diet by, for example, decade and region. Combining regions into a wider area (e.g. the North Sea) could be done by weighted estimates, where weights could be calculated based on the spatial distribution of porpoises from habitat-based models. • For central place foragers (seals), combining diet estimates for different regions, seasons and years will require weighting according to the size of local seal populations (which could be based on haul-out count surveys). ICES | WGMME 2021 | 75 2.3.2 Predator diets for ECOPATH North Sea modelling Marine mammal diets typically vary in space and in time (annually, and seasonally) and diet data are typically available sporadically in space and time. The ECOPATH modelling framework for the North Sea will treat each marine mammal predator as a single population that is assumed to mix freely over the whole area. As such, it will be assumed that any observed regional, seasonal and/or inter-annual variation in diet results from differences in local prey abundance. The WG noted that there are few data for 1991, the base year of the ECOPATH model. Notwithstanding this, the following analysis steps are proposed to aggregate diet estimates from multiple locations and collection dates, to provide inputs in the form of a diet table for ECOPATH, for a given year Y at a whole-North-Sea scale. The same logic could be used to produce aggregate estimates of diet for subareas of the North Sea in future model runs. For each species under consideration, it is required to decide upon a time ‘window’ over which diet data are to be attributed to year Y (1991 in this case): this must be long enough to allow reasonable spatial/seasonal coverage by the diet sampling. For harbour porpoise, stranded and bycaught animals are used in the estimation of diets from gastro-intestinal tract (GIT) contents. Harbour porpoises have a high metabolic rate and limited energy storage capacity and therefore have high feeding rates. GIT diet information is associated with a geographical area where they obtained their last meal. Estimating the most likely foraging area of stranded animals is challenging, because carcasses could have drifted for a considerable period at sea before stranding. A way to estimate this has been described by Ransijn et al. (in review). Using such estimates, data can be aggregated and attributed to a defined region. An estimate of the number of animals in this region could be derived from a spatial model of (seasonal) population density (e.g. Gilles et al., 2016). For seals, diets are estimated from the analysis of hard prey remains in faecal samples collected from haul-out sites. The relative size of the local seal population that is associated with this diet can be estimated from haul-out counts. Such counts could be corrected for animals at sea, using telemetry-based correction factors, but this is not required if the proportion at sea can be assumed to be consistent among haul-out sites. For any species of marine mammal, consuming a variety of prey species, numbered 1 to M, the following steps are suggested, to produce a single point estimate for diet in a given period and area. i. Assemble all available diet estimates in the area and period. A diet estimate is a vector of proportions (p1, p2 … pM)x,t with associated location x and date t. ii. Assemble estimates of the size of the marine mammal “population” associated with each diet sample, Nx,t (see above). This number can vary by place, year and/or season, as appropriate, and therefore can allow for seasonal variation in density. iii. The aggregated diet estimate will be given by (𝑝𝑝1,𝑝𝑝2 . . . 𝑝𝑝𝑀𝑀)𝑥𝑥,𝑡𝑡=∑𝑁𝑁𝑥𝑥,𝑡𝑡𝑥𝑥,𝑡𝑡(𝑝𝑝1,𝑝𝑝2 . . . 𝑝𝑝𝑀𝑀)𝑥𝑥,𝑡𝑡 ∑𝑁𝑁𝑥𝑥,𝑡𝑡𝑥𝑥,𝑡𝑡 To estimate uncertainty in this estimate, a protocol to incorporate uncertainties in the estimates of diet and “population” size is required; a bootstrap resampling approach may be appropriate. 76 | ICES SCIENTIFIC REPORTS 3:19 | ICES 2.4 Discussion A number of issues arise regarding the provision of diet estimates to facilitate the modelling being done through WGBIODIV. For the ECOPATH model, the sparsity of marine mammal diet data in the baseline year 1991 will require utilising data from a wider time period using, for example, the methodology proposed above. Examination of variation of diet estimates over a relevant period of time could inform how well the necessary assumption that the diet so estimated is representative of 1991 is being met. There have been shifts in the distribution and abundance of marine mammal populations into the southern North Sea since the 1990s to the present (harbour porpoise: Hammond et al., 2013; grey seals: Brasseur et al., 2015; ToR A; harbour seals: Brasseur, 2018; ToR A). If these changes were influenced by predation, the diet in more recent years may not be a good refection of diet in 1991. For grey seals, there are comprehensive data from the 1980s, 2002 and 2010/2011, which do show seasonal and interannual changes (Hammond and Wilson, 2016). For this predator species, it will be interesting to see whether a model parameterised with the early diet data can reflect changes in diet through time. For estimating diet as input to the WGBIODIV modelling, Table 2.1 catalogues the extensive information available from marine mammal diet studies from the North Atlantic, focussing on the North Sea. These include seal and cetacean diets, from opportunistic sampling from bycatch/strandings, and from some opportunistic but mostly targeted scat collections. The example studies presented above describe more detail in some cases. Although providing information on diet for WGBIODIV modelling will be challenging, the available data show that it is worth pursuing, and that it should be possible to provide useful information. The WG considered a number of potential issues with how the ECOPATH and prey guild models may use the information provided. Some marine mammal predators have a broad diet, and it is not clear how prey guild modelling approaches may be affected by this. For example, as Table 2.2 illustrates, many prey types may occur very infrequently, so that there is considerable uncertainty whether all possible prey consumed are included in samples. For grey seals at least, it is hoped that a comprehensive list of prey species, such as given in Table 2.2 and estimates of consumption for the most important prey in terms of biomass, such as given in Table 2.3, will provide good information for the cluster analysis. For ECOPATH modelling, the WG discussed the possible implications of aggregating species into functional groups, which may combine prey species for which marine mammal feeding preference is not equivalent. Predator-prey interactions might then be difficult to reproduce correctly, especially if the relative size of those prey populations change. Marine mammals occur over large spatial scales, but the emergent properties of their foraging are likely driven by decisions made at smaller scales. ECOPATH models deal with species interactions over such large spatial scales (e.g. the North Sea) and it is not clear how well they will capture the emergent properties of marine mammal foraging. Implementation of the ECOSPACE model approach may help to reconcile these differences in scale and therefore reproduce the spatial variation in marine mammal diets that have been observed (e.g. Hammond and Wilson, 2016 for grey seals). Model validation may be possible, based on comparison between modelled and observed spatial and temporal variation. Similarly, it is not clear how the lack of seasonality in the ECOPATH model will affect its ability to represent the strong seasonal variation in marine mammal diet observed, presumed to be driven primarily by changes in prey distribution but also by seasonal changes in marine mammal energetic requirements and prey quality. However, if seasonal variation in diet is consistent ICES | WGMME 2021 | 77 among years, the simplification of the annual temporal resolution in ECOPATH may be sufficient to capture any effects. The WG agreed to focus on working with WGBIODIV modellers to ensure that the diet information provided is as robust and comprehensive as possible for the purpose to which it will be put within the ECOPATH and prey guild modelling approaches. Robustness of the diet information needs to consider the most appropriate way to implement the methodology proposed above to capture temporal (seasonal and annual) and spatial variation in diet. In parallel, the WG needs to make progress on assembling the most appropriate diet datasets and results highlighted in Table 2.1 to enable calculations to be make, ideally in time for next year’s meeting. Some datasets/analyses are incomplete, and consideration needs to be given how to make progress with these if they are identified as important in the context of providing information to WGBIODIV. 2.5 References Aarts, G., Brasseur, S., Poos, J. J., Schop, J., Kirkwood, R., van Kooten, T., Mul, E., Reijnders, P., Rijnsdorp, A. D. and Tulp, I. 2019. 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Manage. 9(3): 167–178, 2007. 88 | ICES SCIENTIFIC REPORTS 3:19 | ICES 3.1.3 Review of EU and US legislation requirements for monitoring marine mammal bycatch 3.1.3.1 Policy background European Union. The basic legislation for EU fisheries policy is Regulation 1380/2013 of the Common Fisheries Policy (CFP), an instrument for the management of fisheries aimed at enhancing the sustainability of fish stocks (Khalilian et al., 2010). Regulation 1380/2013 supports the need to protect marine biodiversity and for fisheries to be managed in a way that is consistent with the Habitats Directive (92/43/EEC2) and the Marine Strategy Framework Directive (MSFD) (2008/56/EC). The Habitats Directive and the MSFD set out specific requirements for Member State (MS) with regard to the protection of marine mammals. EU Regulation 812/2004, the main fisheries legislation governing cetacean bycatch, obliged MS to monitor, mitigate and report annually on bycatch using at-sea observer schemes. Compliance with Regulation 812/2004 was low (e.g. monitoring incidental catches of cetaceans by on-board observers of large vessels) and some measures did not apply to more impactful fisheries. As described above, Regulation 812/2004 was replaced with Regulation 1241/2019 (Table 2). Annex XIII of said Regulation 1241/2019 is dedicated to monitoring measures and the reduction of incidental catches of sensitive species. However, Regulation 1241/2019 no longer requires an annual reporting as Regulation 812/2004 (Dolman et al., 2021). Assessments of mortality levels due to incidental bycatch are required to fulfil the objectives of the MSFD, which requires MS to establish mortality thresholds. MS are encouraged to work at sub-regional scale by cooperating with neighbouring MS, especially for highly mobile species. This includes the design and implementation of monitoring programmes to ensure reliable bycatch estimates are obtained. United States. The US Marine Mammal Protection Act (MMPA) established a national policy in 1972 to protect marine mammals and their habitat. Among the key aspects of this legislation are: (1) a shift from the metric of maximum sustainable yield (MSY) to optimal sustainable population (OSP), (2) banning the importation of commercial fish or products that are known to contribute to marine mammal bycatch, and (3) primary and secondary embargoes. The MMPA was reauthorized in 1994 to require the National Oceanic and Atmospheric Administration (NOAA) to use science-based research to assess marine mammal populations. Specifically, Sections 117 and 118 include a requirement for regular assessments for each stock of marine mammals in the USA, and setting a numeric threshold for the maximum number of marine mammals that can safely be removed from a stock or population without causing depletion or impeding recovery, termed Potential Biological Removal (PBR; Wade, 1998). In 2017, NOAA enacted a new rule that fisheries of countries exporting seafood to the United States must comply with provisions within the MMPA (Williams et al., 2016). Bycatch mitigation is also addressed in the Endangered Species Act and Magnuson-Stevens Fishery Conservation and Management Act. 3.1.3.2 Legal requirements for monitoring bycatch European Union. There are a number of legislative instruments related to bycatch of Protected Endangered or Threatened Species (PETS) in the European Union, ICES Member Countries, and Regional Fisheries Management Organisations (RFMOs). Some RFMOs may have binding regulations on bycatch reporting (ICES, 2020a). However, obligations to monitor and collect these data lie with MS, who are expected to cooperate with each other and the European Commission to coordinate data collection activities within the same region. Data compilation is typically done through Regional Coordination Groups that identify and prioritise the fishery/species combinations to be sampled for incidental bycatch under the revised EU Data Collection Framework (ICES, 2020a). Measures to monitor and mitigate bycatch are also required by the EU Habitats Directive (1992/43/EC) under the system of protection, which EU MS need to establish for species listed in Annex IV. To fulfil objectives of the EU Marine Strategy Framework Directive ICES | WGMME 2021 | 89 (2008/56/EC), data by fleet segments are used to identify métiers of greatest bycatch concern. Further, Article 8 of the MSFD requires MS to deliver assessments of bycatch for reporting in 2024. Most of the background information assembled by ICES for its annual bycatch advice since 2007 has come from previous EU MS reports, which were required under Regulation 812/2004 (later replaced by Regulation 2019/1241; see Policy background). Article 18(1) of EU Regulation 2017/1004 states “... Member States, the Commission, scientific advisory bodies and any relevant end-users of scientific data shall cooperate to develop compatible data storage and exchange systems... facilitate dissemination of information to other interested parties...may take the form of regional databases”. United States. Strandings data come from and also feed into NOAA’s 3-part strategy to govern interactions between marine mammals and commercial fisheries. Specific monitoring and mitigation strategies include: (1) marine mammal stock assessment reports, (2) a registration and marine mammal mortality monitoring program for certain commercial fisheries, and (3) implementation of Take Reduction Plans (TRPs). The Northeast Fisheries Science Center (Protected Species Branch) prepares annual reports on the results of analyses and injury determinations for marine mammals interacting with humans, including bycatches of baleen whales, small cetaceans and pinnipeds (NOAA 2021). The focus of the database is on the Northeast / Atlantic coast and the US Gulf of Mexico and the earliest strandings report dates back to 1999. Each report documents serious injuries and mortalities (bycatch, vessel strikes, etc.) by US region, statistical area, and injury determinations over 5-year periods (e.g. 2012–2016). Reports in the database also cover operations by fishery (gillnet and trawl) for cetacean and pinniped bycatch over 1 or 2year periods, and region (Northeast, New England, and/or Mid-Atlantic), dating back to 2007. Other metrics consistently tracked across reports include: (1) number of observer trips, (2) observer coverage, and (3) coefficient of variation (relative dispersion around the mean). 3.1.3.3 Challenges and lessons learnt Policies to monitor and mitigate bycatch are limited by the quantity and quality of data available, in terms of which fisheries are covered and how well they are covered, which in turn is influenced by the legislation (and the extent to which it is implemented). In Europe, the onus lies with individual MS to implement monitoring programmes, and there is no longer a requirement to accommodate on-board observers. Regulation 812/2004 required MS to design and implement monitoring schemes for incidental catches of cetaceans with independent observers (ICES, 2017), but not all MS complied, and this requirement was deleted in Regulation 2019/1241. The EU MSFD and Habitats Directive also provide specific requirements for MS regarding the monitoring and protection of at-risk species. These are obligations, not transposed to law like the CFP, but in theory should be transposed into legislation at the MS level. The Habitats Directive requires MS to monitor the capture and killing of animal species listed in Annex IV. While this is similar to requirements of the US MMPA, the monitoring system has to be implemented by each MS. According to Article 17 of Directive 92/43, MS shall report every six years on the implementation of the Directive, which is consolidated as an implementation report released by the European Commission. As of 2020, the Commission has published two such implementation reports. Dynamic changes in habitat and species distributions together with inconsistent measures of fishing effort limit accurate estimates of bycatch. Key challenges to monitoring bycatch in the EU are: (1) the different ways in which effort is reported by Member States, (2) paucity of data for some fleet métiers, and (3) establishing mortality thresholds for PETS populations. For example, Norway (while not a MS) uses landings to estimate total bycatch, while Iceland uses kilometres of nets from observed effort data. Strandings data are collected throughout the northern Atlantic and stored in databases using different software and schemas (J. Haelters, pers. comm., 17 February 2021). Following recommendations from ICES Working Group on Bycatch of Protected Species (WGBYC), fishing effort has been 90 | ICES SCIENTIFIC REPORTS 3:19 | ICES made a mandatory field within the Regional Database and Estimation System (RDBES) exchange format and is reported in the ICES database as number of trips and days at sea (NAMMCO, 2019). For monitoring of fishing activities, small-scale fisheries have long been overlooked because smaller vessels (< 1 2m) are not covered by VMS or AIS (Peltier et al., 2020). Observer coverage can also vary greatly across MS and species (Saavedra et al., 2018). While a precautionary principle to mitigate bycatch can be aspirationally better, policy implementation (i.e. compliance and enforcement) has often been less watertight in the EU compared to the more reactionary approach of the United States with the MMPA. Successes of the MMPA in monitoring and mitigating bycatch include: (1) amendments that adopted PBR as a numeric threshold for the maximum number of animals that can be removed from each stock, (2) mandate for NOAA National Marine Fisheries Service to establish monitoring programmes that obtain statistically reliable estimates of incidental mortality and serious injury during commercial fishing operations, and (3) required formation of a multi-stakeholder group, called a Take Reduction Team, if a strategic stock interacts with a fishery categorized as posing risk of occasional to frequent incidental mortality (McDonald et al., 2016). With respect to monitoring bycatch in the EU, Habitats Directive and MSFD requirements are clear for the organisation of species and habitat monitoring networks. Current deficiencies in monitoring are due to poor implementation of the legislation at the national and regional scales. ICES has issued official data calls since 2018 to improve consistency in the reporting of incidental bycatch data at a regional scale through the EU Data Collection Framework (Regulation 2017/1004) (ICES, 2020). WGBYC collates and analyses these data. The Working Group on Spatial Fisheries Data (WGSFD) collates and analyses spatial data to evaluate fishing effort, intensity, and frequency to estimate bycatch risk. The Working Group on Commercial Catches (WGCATCH) documents national fishery sampling schemes and establishes best practice and guidelines on sampling and estimation procedures. WGMME now tracks which intergovernmental organisations collate strandings data, and if these records include bycatch information (Table 3.1). It is expected that these data will be provided in the future through the aforementioned RDBES (ICES, 2020a). With an authoritative bycatch estimation database in place, ICES could assist EU Members States with: (1) developing sampling protocols, (2) establishing common formats for data reporting/ storing, and (3) techniques for indicator assessment and threshold setting. 3.2 Reviews of recent publications and reports 3.2.1 Summary of FAO Guidelines to Prevent and Reduce Bycatch of Marine Mammals in Capture Fisheries. The FAO reviewed four main technical measures to prevent and reduce marine mammal bycatch (FAO, 2021): Spatial closures, Acoustic alerting or deterrent devices, Modifications to fishing gear, and Changes to fishing operations. 1. Spatial closures (often referred to as time–area closures) to restrict gillnet and pot fishing have been established in several countries in response to concerns about marine mammal bycatch (including both ‘consequence closures’, e.g. to protect harbour porpoise in eastern United States, and ‘dynamic closures’, e.g. seasonal closures for North Atlantic right whales in NE United States and Canada). In some cases, a combination of seasonal and permanent closures of gillnet fisheries have been introduced (e.g. to reduce bycatch interactions with Australian sea lions in South Australia). However, only a few studies have quantified the effect of closures on the bycatch species or populations of marine mammals for which they were established (e.g. tag–recapture studies of Hector’s ICES | WGMME 2021 | 91 dolphins following gillnet closures in New Zealand). All these studies showed how adopting spatial closures as a principal management response for the reduction of marine mammal bycatch did not achieve adequate, or indeed measurable, population recovery; although there may be circumstances where it could be appropriate, for example, to help stabilise populations. It is important that the location, design and management of spatial closures be supported by adequate information, monitoring and enforcement. In particular, care should be taken not to simply move the problem elsewhere by redirecting fishing effort. Dialogue and working closely with fishers are critically important, as the latter generally oppose any form of spatial closure. 2. Acoustic alerting or deterrent devices (ADD; primarily pingers) have been proved effective at reducing bycatch for species such as harbour porpoise in gillnet fisheries (see also Table 3.2). They are designed to alter behaviour in particular marine mammal species, but can have unintended consequences on the target or other species (e.g. exclusion from wide areas or attraction – a ‘dinner-bell’ effect). Habituation has not been reported from fisheries in the east (multispecies gillnet) and west-coast (driftnet) fisheries of the United States, which have long-term monitoring data. Acoustic deterrent devices may have species-specific effects, being effective only on certain species and in particular fishery contexts, and their use should be subjected to ongoing monitoring. 3. Modifications to fishing gear can take a variety of forms, a few of which are detailed below. Excluder devices (such as grids) have been used in trawl fisheries. Excluder devices are typically tailored to individual fisheries, fishing vessels and bycatch species. One disadvantage of excluder devices is that they effectively render on-board observers blind to the true extent of marine mammal interactions. Underwater video monitoring is essential to monitor interaction levels, detect mortality, and optimise excluder design. Weak ropes in pot and gillnets, as well as weak gillnet webbing, may help entangled baleen whales shed gear, thereby reducing mortality and serious injury. These have been applied in the United States under the Atlantic Large Whale Take Reduction Plan, for example with weak links placed just below the buoy in gillnet and pots, at the uppermost portion of the vertical line. The incorporation of weak links below the buoy (in pots and gillnet fishing) has reduced either the incidence or severity of large whale entanglements off the east coast of the United States. Any gear modification should be trialled in realistic field conditions and its success assessed with adequately designed (and statistically powered) studies in order to determine their effectiveness. 4. Changes to fishing operations. Changes in the way that fishing operations are conducted can reduce marine mammal bycatch. For example, various procedures have been executed in the eastern tropical Pacific such as changing the practice of setting purse-seine nets on dolphins to catch tuna, and trying to facilitate the escape of dolphins trapped in nets during hauling (by reversing the vessel after the majority of the net is on board in combination with the use of a Medina panel). For pot, gillnet, longline, and other similar static gear types, in which multigear strings are used, reducing the ratio of vertical lines to units of gear would limit the number of vertical lines that marine mammals can encounter. However, there have been reports that, by increasing the diameter of buoy lines to support heavier bottom-set gear, this may decrease the probability that marine mammals can break free of it. Increasing the number of pots per string will also increase groundline length, which in turns causes the entanglement of marine mammals. Gear switching away from pots, for example, to longlines has been shown to reduce seal bycatch in the Baltic, and switching from gillnets to longlines in Iceland reduced harbour porpoise bycatch. Attention needs to be paid to effects upon species composition and size selectivity, but there may be actual commercial benefits in higher catch quality due to shorter soak times. Other gear switches such as from gillnets to trawls, may be promising alternatives in certain contexts. As previously, any changes to fishing operations 92 | ICES SCIENTIFIC REPORTS 3:19 | ICES should be trialled in realistic field conditions and its success assessed with adequately designed (and statistically powered) studies in order to determine their effectiveness and understand the possibly context-dependent conditions of success or failure. 3.2.2 Summary of WWF report on using camera technology to monitor, and support mitigation of, wildlife bycatch in fisheries Course et al. (2020)2 reviewed the use of Remote Electronic Monitoring (REM) to quantify and study bycatch of PETS, including seabirds, marine mammals, sea turtles, elasmobranchs and sea snakes. Five case studies of REM to assist in addressing the problem of unintentional killing of PETS are presented and contrasted, before recommendations are issued. The term ‘Remote Electronic Monitoring’ (hereafter REM) is often used to refer to several different types of technology and not just systems with camera technology included. Course et al. (2020) draw distinctions between several terms (e.g. “electronically monitored” vs. “electronically reporting”), and clarify some terminology: • E-log refers to electronic logbooks in which fishers record their catches at sea or immediately upon landing. It is basically an electronic version of a standard paper logbook, which relies on the fishers to enter their catch directly into a database via on-screen software. However, e-log remains a form of self-reporting, not a form of independent monitoring. E-log alone does not provide independence and verification of the collected data and it does not address some strong incentives against accurate reporting; • E-tracking refers to both VMS (satellite-transmitted) and AIS (VHF-transmitted) tracking technology. AIS and VMS are both useful tools for monitoring where vessels are and to indicate what they may be doing, but they do not record evidence of fishing activity, they only imply probable activity through interpretation of speed data and positional data; • REM refers to monitoring systems that typically comprise video-capable cameras, fishing activity sensors, a satellite modem, GPS receiver, a user interface and a system control centre, and which can document fishing voyages in their entirety, or some subset of time or activities on a vessel. A recent technical report from the European Fisheries Control Agency (EFCA) recommends the specifications that a REM system should meet for monitoring European fisheries (available at https://www.efca.europa.eu/en/content/technical-guidelines-and-specifications-implementation-remote-electronic-monitoring-remeu). Five case studies are described by Course et al. (2020): 1. Australia’s Eastern Tuna and Billfish Fishery (longlines), with an initial focus on seabird bycatch, but also looking at cetacean bycatch. Over the first two years of operational REM deployments in the Eastern Tuna and Billfish Fishery, image analysts detected over 30% more seabird interactions than were reported in logbooks. However, for turtles and marine mammals, logbooks documented more interactions than were recorded from images, a difference which may be due to PETS falling from the gear and not being landed on deck in view of the camera, or animals being released by crew when still in the water and out of camera view. 2. Australian Southern and Eastern Scalefish and Shark Fishery (gillnets and line-fishing gears) with an initial concern for the Australian sea lion. After the initial deployment of REM systems for the pilot project, there was a marked increase in dolphin interactions 2 https://www.wwf.org.uk/sites/default/files/2020-11/whatsinthenetfinal.pdf ICES | WGMME 2021 | 93 reported by fishers. In the four years before REM, fishers had reported a total of 0–6 dolphin captures annually. This increased to 21 and 44 respectively, in each of the two fishing years 2010/2011 and 2011/2012. All dolphin capture reports in this two-year period were from vessels carrying REM systems. Logbook reports of protected species interactions increased after REM was introduced, compared to prior to its introduction. 3. Danish inshore gillnet fisheries, which started as a pilot study in 2009–2010, but has been running for ten years now. This case study established how REM was more accurate for collecting bycatch data than using unverified self-reported data. REM was also more cost-effective than at-sea observers. Although the project has been ongoing for ten years, it is limited in the number of vessels equipped with REM (eight vessels). 4. Tropical tuna purse-seine fishery. REM has been trialled in several different purse-seine fisheries including the Ivory Coast, Ghana, the Indian ocean, the Seychelles and the eastern Pacific Ocean tuna fishery. Among those trials, only the Ghanaian programme can be considered operational, because it has been operating on its entire purse-seine fleet for several years. However, monitoring is not aimed at reporting interactions with PETS and the main focus is ensuring that Ghanaian tuna is not banned from EU markets due to a lack of transparency and potential Illegal, unreported and unregulated (IUU) activities. The quality of the data for the monitoring of PETS interactions and bycatch quantification has been questioned. 5. Artisanal and/or small-scale fisheries. Course et al. (2020) stress the importance of artisanal or small-scale fisheries: it is estimated that 95% of vessels can be classified as smallscale and that they contribute over 50% to the world’s total catches and involve 50 million fishers. Vessels can be typically less than 10 m in overall length and some may have no engine to power the vessel, never mind a REM system, so it may not be possible (even if appropriate), to monitor using video technology. However, some fisheries have the potential for high levels of interactions with PETS. One additional benefit to REM in small scale fisheries is the vessel tracking aspect of the system to provide effort data and the potential to improve safety of these vessels. The authors discuss the challenges involved in setting up a REM scheme for these fisheries, point to relevant/promising technological solutions, and describe some existing initiatives. They provide an example of an operational REM programme in an artisanal fishery in inshore Peruvian waters using gillnets. This study found a low correlation in bycatch counts between observers and REM, thought to be due to how the cameras were configured and positioned. However, the study concluded that REM is an excellent low-cost alternative to using at-sea observers and could provide cost savings of over 50%, although issues related to data storage and camera resolution remain to be resolved. For each case study, elements of best practice demonstrated for setting up an operational REM (pilot) programme are highlighted. Two theoretical examples are also provided: setting up an operational REM programme for (i) an industrial trawl fishery involving ten vessels, and (ii) a coastal gillnet fishery involving 100 vessels. These examples show-case realistic set-ups of a completely de novo monitoring programme with REM. More widespread use of REM to monitor PETS bycatch is realistic, feasible and cost-effective. The pros of REM include costs-saving, a better coverage (because REM can be extended to smallscale fisheries) and less observer bias. REM improves the accuracy of self-reporting by groundtruthing: it is a clear deterrent to illegal or irresponsible practices. Among the challenges to set up an operational REM scheme are the development of a dataflow and an analytical pipeline that uses Machine-learning techniques to analyse the video/photo data in a timely manner. The complexity of this step should not be underestimated as timeliness and algorithmic transparency are both critical to success. While there is some resistance to REM by fishers, the report lists 94 | ICES SCIENTIFIC REPORTS 3:19 | ICES recommendations for greater acceptance of REM through advisory bodies, Regional Fisheries Management Organisations (RFMOs), market-based solutions (e.g. labels, supply chains should consider REM as a condition of seafood sourcing) or legislation. Nevertheless, the effective implementation of REM projects and programmes remains highly context-specific as can be seen from the five case studies. 3.2.3 Summary of ASCOBANS Reports WGMME reviewed and summarized information on bycatch and strandings included in the reports from the parties submitted to ASCOBANS for the period 2016–2018. Belgium, reporting period 2017–2019: The protocol by Kuiken (1994) was followed in necropsies. Necropsies are conducted in about 50% of the stranded harbour porpoises (Phocoena phocoena). Only very few cetaceans other than harbour porpoises are found on Belgian beaches. Depending on their decomposition, they are also necropsied. Between 2017 and 2019, the stranding network registered 16 harbour porpoises suspected of having been bycaught out of a total of 233 stranded animals, but with known or suspected cause of death for only 78 animals. Additionally, one white-beaked dolphin was confirmed as bycaught in ICES Division 4.c. The gear type was mostly unknown but, when known corresponded to trammelnets or gillnets, but at least in one case a harbour porpoise was bycaught in recreational beach fisheries using a fykenet. Other causes of death included predation by grey seals (Halichoerus grypus), infection and starvation. Germany, reporting period 2016–2019: National protocols (i.e. Siebert et al., 2001) were used to perform necropsies of 1010 carcasses. The cause of death was determined in 9.5% of cases corresponding to; suspected bycatch (3.3%), confirmed bycatch (1.7%), cachexia (1.6%), suspected predation (0.9%), suspected trauma (0.8%), suffocation due to fish in larynx (0.7%), suspected septicaemia (0.3%), and death of mother (0.2%). Three harbour porpoises were reported by fishers as bycaught in static nets in 2017. The Netherlands, reporting period 2016–2019: The ASCOBANS guidelines on best practices on cetacean post-mortem investigations and tissue sampling (2019) were followed to perform necropsies of 220 carcasses (217 harbour porpoises, one long-finned pilot whale Globicephala melas, one Sowerby’s beaked whale Mesoplodon bidens and one white-beaked dolphin Lagenorhyncus albirotris). Besides bycatch other identified main causes of death included grey seal attacks, infectious diseases and emaciation. Additional causes of death included bacterial infection, starvation, trauma, and perinatal death. Using REM, three harbour porpoises were reported as bycaught in trammel nets and gillnets. France, reporting period 2016–2018: National protocols (Van Canneyt et al., 2015) were followed to perform necropsies of 514 carcasses of ten cetacean species (common dolphin Delphinus delphis, bottlenose dolphin Tursiops truncatus, striped dolphin Stenella caeruleoalba, long-finned pilot whale, white-beaked dolphin, Risso’s dolphin Grampus griseus, harbour porpoise, Cuvier’s beaked whale Ziphius cavirostris, Sowerby’s beaked whale, Northern bottlenose whale Hyperoodon ampullatus and pygmy sperm whale Kogia breviceps). Bycatch was reported as the cause of death for 50% of the strandings across species and for 90% of the common dolphin strandings. 5% of the strandings were live strandings. Fishery observers on board reported 126 common dolphins, 13 harbour porpoises, five longfinned pilot whales and one striped dolphin as bycaught from ICES subareas 7 and 8 in otter trawls, pair trawls, gillnets and trammelnets. In addition, fishers reported 54 common dolphins as bycatch in pelagic pair trawlers in Subarea 8. The stranding network reported three harbour porpoises bycaught in recreational beach fisheries using gillnets in ICES Division 7.d in 2018. ICES | WGMME 2021 | 95 United Kingdom, reporting period 2016–2019: Twelve species of cetaceans were recorded as stranded in the period 2016–2019; common dolphin, bottlenose dolphin, striped dolphin, longfinned pilot whale, white-beaked dolphin, Atlantic white-sided dolphin Lagenorhyncus acutus, Risso’s dolphin, killer whale, harbour porpoise, Cuvier’s beaked whale, Sowerby’s beaked whale, Northern bottlenose whale and pygmy sperm whale. From the total stranded cetaceans in 2016–2019 (n=3182), 65 were identified as dead at sea or entangled and 186 were live-stranded. National protocols by the UK Cetacean Strandings Investigation Programme (http://ukstrandings.org/) were followed to perform necropsies of 515 carcasses of all the recorded species. Following necropsies, the stranding network registered 61 bycaught cetaceans (43 common dolphins and 18 harbour porpoises) in ICES subareas 6 and 7. In addition, necropsies of a killer whale (Orcinus orca) and a Northern bottlenose whale stranded in ICES subareas 6 and 7 and a Sowerby’s beaked whale stranded in ICES Division 4.b, indicated that the animals died due to entanglement in fishing gear. The gear type was unknown in all cases of bycatch and entanglement. Monitoring through the EU Data Collection Framework registered one common dolphin caught in static nets in Division 7.e in 2017. 3.2.4 Summary of the Progress Report on the Jastarnia Plan: The Recovery Plan for the Harbour Porpoise in the Baltic Proper (Carlén and Evans, 2020) 3.2.4.1 Threats and population status Understanding of the human threats that impact on population status is necessary to inform appropriate conservation action. Bycatch in gillnet fisheries has been recognised as the primary threat for the survival of the Baltic harbour porpoise population. Other concerns are high contaminant levels, anthropogenic noise and overfishing. The continuing eutrophication of the Baltic Sea increases the area of seabed devoid of oxygen, which has a negative impact on prey species of harbour porpoise. A lack of top predators such as cod and porpoises is thought to be allowing numbers of sprat and herring to increase to the extent that it is affecting the nutritional status of these prey species. A similar link has been proposed as affecting grey seals in the Baltic (Kauhala et al., 2017). Although warming climate decreases ice coverage in the Baltic Sea during winter and could thus be considered to have a positive impact on harbour porpoises, climate change may also influence the distribution, availability and quality of harbour porpoise prey. The overall effects that changing climate has on the Baltic Sea ecosystem remain poorly understood. There is currently a HELCOM process to produce fact sheets on so called “secondary parameters” for effects of climate change, and “marine mammals” is one of those secondary parameters. IUCN (Hammond et al., 2008) has classified the Baltic subpopulation of the harbour porpoise as critically endangered. However, assessments by the nine individual countries bordering the Baltic Sea lead to eight different classifications, ranging from “Probably extinct” (Latvia) to “Least concern” (Denmark and Poland), as well as including “Not assessed” (Finland) and “Not listed” (Lithuania). Part of the issue is that, in some countries, both Belt Sea and Baltic proper subpopulations are present but are not assessed separately. In their reporting for Habitats Directive Article 17, Denmark, Germany, Poland, and Sweden all report the status of harbour porpoises in the Baltic marine region as “Unfavourable-Bad”, i.e. the least favourable category. Finland, Estonia, Latvia and Lithuania have not reported on the harbour porpoise. 96 | ICES SCIENTIFIC REPORTS 3:19 | ICES 3.2.4.2 Public Awareness in the Baltic The rarity of harbour porpoises in the Baltic Proper has meant that over large parts of the region, the public remains unaware of its existence. There have been numerous initiatives to increase awareness and highlight threats to porpoises, but several of those described below were most active a few years ago. There is a need to both sustain such efforts and develop new campaigns in all the countries bordering the Baltic Sea, especially in the eastern Baltic where this would constitute an important first step. Such initiatives should involve international and national nongovernmental organisations with direct connections to the public, as well as museums, aquaria, governmental agencies and ministries in all countries. Public awareness may become even more important to support conservation efforts following from the 2019 special request to ICES for advice3 on emergency measures to prevent bycatch of Baltic Proper harbour porpoise (ICES, 2020b) and steps taken by the European Commission to minimise bycatch. In Poland, Hel Marine Station (University of Gdańsk, UG) has had a long history of raising awareness about harbour porpoises, while the WWF-UG voluntary network Blue Patrol assists in reporting stranded animals and delivering carcasses to Hel Marine Station. In the 2020 Swedish Red List, the Baltic Proper harbour porpoise is listed as Critically Endangered, and this has been widely publicized, e.g. by the Swedish Species Information Centre and via radio, TV, and social media. The Swedish authorities have consulted fishers about the regulation of fisheries in protected areas. The Swedish Museum of Natural History runs a citizen science programme to collect harbour porpoise sightings. Other organisations involved in publicizing the threats to Baltic porpoise include WWF Sweden, the Swedish Society for Nature Conservation, Coalition Clean Baltic (CCB) and Sweden’s largest zoo in Kolmården. In Denmark since 2017, there has been a listening station in Middelfart harbour, where the public can listen in real time to any porpoises present around the hydrophone. Danish Society for Nature Conservation launched a small campaign on the harbour porpoise in 2020. Although there is currently no public sightings programme or a comprehensive strandings monitoring scheme, reporting of strandings to the Maritime Museum in Esbjerg (https://fimus.dk) is encouraged. In Germany, there are sightings and strandings programmes involving the public. For Schleswig-Holstein, these are coordinated by Terrestrial and Aquatic Wildlife Research (ITAW) in Büsum; for Mecklenburg-West Pomerania, they are administered by the German Oceanographic Museum in Stralsund. The museum also participates in the annual International Day of the Baltic Harbour Porpoise (coordinated by ASCOBANS), has run a marine mammal science education project and hosted an exhibition (“Die letzten 300”, in collaboration with NGOs and ASCOBANS) which was visited by an estimated 30 000 people, as well as producing various apps (“OstSeeTiere” - Baltic Sea Animals4 and “Be the Whale” 1 and 2 about humpback whale and beluga respectively5) designed to make children aware of threats to cetaceans. Project “STELLA” (2016–2019) involved close cooperation with fishers to develop of alternative management approaches and fishing gear. In Finland, the Ministry of the Environment has run a public reporting scheme for porpoise sightings since 2001, and regularly issues information about the current situation of harbour porpoise. Until its closure in 2015, the Tampere Dolphinarium in Finland ran an education programme. In Lithuania, a harbour porpoise protection plan was initiated in 2014, with flyers and 3 https://www.ices.dk/sites/pub/Publication%20Reports/Advice/2020/Special_Requests/eu.2020.04.pdf 4 https://www.deutsches-meeresmuseum.de/wissenschaft/ infothek/sichtungskarte/ 5 https://www.deutsches-meeresmuseum.de/be-the-whale ICES | WGMME 2021 | 97 a short documentary made to raise public awareness6. The Lithuanian Sea Museum (LSM) plans a Baltic Sea Animals and Therapy Centre (BARTC). Russia, Latvia, and Estonia have apparently not run any campaigns to raise public awareness about porpoises in the Baltic. 3.2.4.3 Stakeholder involvement and cooperation Ghost nets have been identified as an important conservation issue. In the international project MARELITT BALTIC (https://www.marelittbaltic.eu/, 2016-), which aims to develop simple, costeffective and environmentally safe methods to (i) identifying and marking derelict gear and (ii) removing it, Swedish and Polish fishers have been dragging parts of the Baltic to collect and remove ghost nets. Such efforts could be expanded to other countries in the Baltic, to benefit harbour porpoise and other marine wildlife. 3.2.5 Key Conclusions and Recommendations Current bycatch levels of harbour porpoises in the Baltic are clearly unsustainable with the current PBR estimated at 0.7 individual per year (2020b). For the Baltic Proper harbour porpoise management unit, to meet the management objective of achieving bycatches below PBR, ICES advised that all fisheries of concern should be closed7. The development and implementation of fishing gears that have a low bycatch risk for harbour porpoises is a high priority (ICES, 2020b). Monitoring and assessing population status is challenging for a population that is so rare over large parts of the Baltic Proper. It is important that all lines of evidence are utilised, including acoustics, opportunistic sightings, and strandings along with life-history information derived from dead animals. Only Germany has a dedicated stranding scheme with good samples of animals necropsied and the other countries could do more to maximise opportunities to obtain data on porpoises. In this context, the perceived status of Baltic porpoises in national Red Data lists for most countries could usefully be updated, especially for Poland which lists a status for the porpoise that is clearly misleading (least concern), although it recognises its conservation status as “Unfavourable-Bad” in its Habitats Directive Article 17 reporting. 3.2.6 Review of recent publications on bycatch and other interactions with fisheries - Interviews with fishers Over the last few years, many publications have highlighted the importance of accounting for the opinion of fishers to better understand the viability of proposed mitigation measures. In the context of increased seal abundance and seal interactions with coastal fisheries in the southern Swedish Baltic Sea (mainly grey seal), Waldo et al. (2020) gathered information about the opinion of local communities (fishers and non-fishers) on proposed management measures to deal with seal depredation. Responses highlighted the necessity of rapidly applying measures to prevent the economic collapse of small-scale, local fisheries. Economic compensation for fishers and subsidies to modify gear were generally viewed favourably as a short-term fix, although fishers concerned that use of alternative gears would reduce fish catches. For a long-term solution, the preferred measure identified by fishers was hunting to control the growing populations of seals. Johansson and Waldo (2020) argued that the achievement of successful measures in the Swedish case would require the involvement of stakeholders and that the small-scale fisheries could be promoted as a sustainable local industry and part of the local cultural heritage. 6 https://www.youtube.com/watch?v=WQYP5T0SCbs 7 https://www.ices.dk/sites/pub/Publication%20Reports/Advice/2020/Special_Requests/eu.2020.04.pdf 104 | ICES SCIENTIFIC REPORTS 3:19 | ICES Milani et al. (2019) used a combination of techniques, including examination of cetacean stranding reports, to characterise interactions between fisheries and cetaceans in the Thracian Sea. Results from 58 dead strandings records revealed that six specimens showed evidences of interactions with fisheries. Four individuals were found entangled in fishing static nets (one Delphinus delphis, two Phocoena phocoena, one Stenella coeruleoalba), and two Tursiops truncatus had pieces of trammelnets in their digestive system. The study also used fisher interviews to investigate negative interactions with cetaceans (see Section 3.2.5), which indicated depredation events and gear damage. Karamanlidis et al. (2020) used fisher interviews to characterise fisheries interactions with the Mediterranean monk seal in waters of Greece, between 2006–2017. Fishers reported bycatch events in the majority of the surveyed areas. Morrocco. Masski and Stéphanis (2018) reviewed information on stranded cetaceans along the coast of Morocco between 1980–2009. A total of 205 strandings was documented, including 180 cases identified to the level of genus and 169 to species. 114 cetaceans presented injuries and mutilations. 11% of cases had sectioned fins, which is a common practise among fishers to release animals entangled in gears. The cetaceans with sectioned fins were mainly dolphins, with a few pilot whales and one minke whale, stranded in the Strait of Gilbraltar, the region of Casablanca, and the Mediterranean area. Most cetaceans with sectioned fins were found around the Strait of Gibraltar, which might be due to the frequent use of driftnets in this region. Tunisia. Karaa et al. (2012) reviewed cetacean stranding records along the coast of Tunisia from 1937 to 2009. A total of 132 stranding events was recorded, involving both Odontoceti and Mysticeti. A cause of stranding was determined in 35.6% of cases. Human-related causes accounted for 24.24% of all stranding events. Bycatch was the main cause of bottlenose dolphins strandings (25/83 individuals; 30%). These numbers should be taken as minimum estimates. 3.3 Forthcoming and current initiatives to reduce bycatch 3.3.1 Entanglement and marine mammals-the Scottish entanglement Alliance programme Marine animal entanglements are a growing and acutely severe problem globally, considered by the International Whaling Commission (IWC) to be the single most significant marine mammal welfare issue of our time (IWC, 2016). Around Scotland, a diverse array of marine animals, including cetaceans and basking sharks inhabit the inshore waters which also provide valuable fishing grounds for static and mobile fishers. The Scottish fishing industry makes a significant contribution to the national economy, and forms the social and cultural backbone of many small fragile coastal communities. However, with thousands of miles of rope and netting associated with these fisheries in the water at any given time, the incidence of entanglement appears to be increasing. Entanglement of marine animals in Scottish waters can be a significant welfare issue, especially to larger, stronger animals who appear able to survive, but not escape, entanglement for longer. Chronic entanglements are eventually fatal either through drowning or the animal succumbing to secondary injuries, infection or debilitation caused by the entanglement. The Scottish Entanglement Alliance (SEA)8 is a partnership between six organisations dedicated to promoting and protecting Scotland’s wildlife, natural heritage and sustainable creel fishing. Initiated by the Scottish Creel Fishermen’s Federation (SCFF) upon recognising a potential issue within their sector, SEA partners aimed to engage directly with the inshore creel fleet to 8 www.scottishentanglement.com ICES | WGMME 2021 | 105 determine 1) if marine animal entanglement is perceived to be an issue within the static sector, and 2) what the risks and consequences of entanglements are from a conservation, welfare, human safety and economic perspective. The programme ran from April 2018 for two years but reporting was delayed due to COVID. A final report is due to be published in April 2021. Key findings are: • Marine animal entanglements have been reported from all regions of Scotland, with some regional hotspots. Minke whales and basking sharks (Cetorhinus maximus) were the most commonly reported species, and the majority were discovered entangled in groundlines. Entanglements were reported all around the coast and their incidence was related to fishing depth, gear length, hauling frequency and target species. • Strandings reports show some seasonality, with humpback entanglements clustering around late spring, minke whales in summer and leatherback turtles (Dermochelys coriacea) in autumn. • The most typically reported entanglement case reported are minke whales, entangled acutely by rope around the tail. In most of these cases the entanglement is rapidly fatal due to drowning or anoxia. The number of fatal humpback entanglements in the strandings database was low (n = 4) but all but one showed evidence of chronic entanglement. This had a significant impact on animal welfare. • The gear type and chronicity of marine animal entanglements varies by species, likely due to a combination of reasons including anatomy, foraging behaviour and distribution. • Interviews with 159 creel fishers (representing approximately 11% of the commercial fleet) revealed that almost half had experienced at least one entanglement between 2008– 2018, with a total of 146 entanglements reported involving at least 12 species of cetacean, shark and turtle. • The results showed that the use of creels is widespread throughout inshore waters off the west coast of Scotland and the data suggest a general upward trend in the number of creel fleets encountered during surveys in recent years. This may corroborate the concerns raised by fishers regarding increasing creel fishing effort around the Scottish coast. • Over 80% of fishers provided measures that they felt could prevent or reduce the risk of entanglement, almost 75% expressed willingness to test mitigation measures, and over 65% expressed interest in training to report entangled animals and/or disentangle them. • 75% of fishers interviewed disagreed with the suggestion that marine animal entanglements have a major economic impact on the Scottish creel fishing sector, either because they had never experienced one, they were very rare, or were not costly when they did occur. • There is significant underreporting of entanglement events in Scottish waters, with less than 5% of entanglements encountered by creel fishers getting reported to the strandings networks. • Sightings data were assessed to identify areas where there was the greatest overlap between sightings of minke whales and creel fleets, and therefore represent the areas where there is the highest relative risk of a whale-creel based interaction occurring that may result in an entanglement. • Photo-identification records of minke whales were assessed for evidence of entanglement. Four percent of animals (n = 9) showed clear evidence of a current or previous entanglement. A further 16% had marks that showed evidence that they may have previously been entangled in fishing gear. • The proportion of animals showing evidence of a previous entanglement has remained consistent with previous estimates with 20% of the live population showing high to moderate evidence of a previous entanglement. • Although the number of entanglement cases reported to the Scottish national strandings network remains low, the incidence has been steadily increasing over the past decade. 106 | ICES SCIENTIFIC REPORTS 3:19 | ICES • There is concern that the extent and incidence of entanglement events in Scottish waters may be sufficient to impact large whale species at a population level. • Further study and trials to assess the feasibility, costs and other implications associated with suggested mitigation measures to reduce entanglement risk including a move toward negatively buoyant ropes, reduced creel fishing effort and ropeless fishing systems were supported by fishers interviewed in this study. • Improved reporting systems for fishers to report and assess entanglements are essential to fill large data gaps in our understanding of the true incidence and nature of interactions between fishing gear and marine mammals. • The creel industry is actively and positively engaging with the issue and further funding is currently being sought to support continuation of this work. 3.3.2 Towards a coordinated assessment and monitoring strategy for marine mammals: project proposal for Bay of Biscay and Iberian Coast The Cetambicion project (“Coordinated Cetacean Assessment, Monitoring and Management strategy in the Bay of Biscay and Iberian Coast sub-region”), funded under the MSFD 2020 call, will run from March 2021 to February 2023. It addresses the urgent need to reduce cetacean bycatch in EU fisheries, consistent with the requirements of the Habitats Directive Marine Strategy Framework Directive and Common Fisheries Policy (Technical Measures Regulation), an urgency highlighted by the 2019 request (by several NGOs) for emergency fisheries measures to reduce bycatch of common dolphins in the Bay of Biscay and of harbour porpoises in the Baltic Sea, on which ICES provided advice to the European Commission in 2020, and following which the Commission requested that France and Spain take action to address the cetacean bycatch issue in Bay of Biscay. An additional driver for reduction in bycatch of cetaceans is the request by the USA that all nations exporting fishery products to the USA should demonstrate that their management of cetacean bycatch is consistent with the requirements of the US Marine Mammal Protection Act. The MSFD 2020 call provided an opportunity to propose work on measures to improve bycatch monitoring and mitigation in the Bay of Biscay and adjacent Iberian coastal waters, thus helping to achieve Good Environmental Status (GES) in relation to Descriptor 1 (D1, Biodiversity) and, specifically, cetacean bycatch (criterion D1C1 and OSPAR common biodiversity indicator M-6). In so doing it will also consider criteria for abundance (D1C2), demographic characteristics (D1C3), distribution pattern and range (D1C4) and habitat (D1C5). The project involves 14 partners from the Member States (MS) France, Spain and Portugal, including government ministries and public research and conservation bodies, who will work in collaboration with professionals and NGOs. It is divided into six work packages: Work package 1 reviews assessment, GES determination and targets based on the 2018 MSFD report for D1 (cetaceans) of the 3 MS, as well as reported monitoring programmes and programmes of measures of the 3 MS. The review will also consider work by OSPAR, ICES groups, ASCOBANS and the IWC. Work package 2 will develop a proposal for coordinated sub-regional assessment, GES determination and monitoring strategy for cetaceans (D1C2, D1C3, D1C4, D1C5). This will comprise: (i) Data gathering and gap analysis including information on relevant pressures; (ii) Establishing the sub-regional list of species, indicators and scale of assessment; (iii) Common approach to GES determination, threshold values and integration rules; (iv) Sub-regional assessment and Definition of coordinated monitoring strategy and programmes. ICES | WGMME 2021 | 107 Work package 3 will develop a proposal for coordinated subregional assessment, GES determination and monitoring strategy for Bycatch (cetaceans). This will comprise: (i) Compilation of the available information on bycatch (previous projects, campaigns, research surveys, stranding schemes, etc.), highlighting knowledge gaps; (ii) Common approach for Risk Assessment; (iii) Common approach to GES determination and threshold values; (iv) Defining coordinated monitoring programmes for by-catch, including improved observer programs and other methods (e.g. video monitoring, stranding networks, logbooks, etc.) to improve estimates of bycatch rate. Work package 4 will develop a proposal of coordinated measures to address cetacean bycatch. This will include several Pilot Projects to assess the efficacy of bycatch reduction devices and procedures, including the use of pingers and excluder devices. It will also collect information and share experience from previous pilot projects and relevant projects, and propose common measures including space-time management measures. Work package 5 concerns communication, stakeholder participation, capacity-building and legacy and Work package 6 provides coordination. 3.3.3 Mediterranean bycatch projects The Med Bycatch Project9 “Understanding Mediterranean multi-taxa ‘bycatch’ of vulnerable species and testing mitigation – a collaborative approach” aims at monitoring and mitigating incidental catches of vulnerable species in Mediterranean fisheries, specifically to (1) collect bycatch data in a standardised way to enable comparison across the region, (2) identify and test mitigation measures to reduce bycatch, (3) raise awareness on bycatch and provide bases for the formulation of national and regional strategies through a collaborative approach. The project focuses on several taxonomic groups, including sea turtles, seabirds, marine mammals, cartilaginous fishes as well as corals and sponges, for which bycatch is a key threat. Data are collected for different fishing gears (i.e. bottom trawls, gillnets and demersal longlines), using several methodologies: fishery-dependent data are obtained from commercial fisheries (e.g. on-board observer programmes, interviews, self-sampling (e.g. logbooks), remote electronic monitoring), and fishery-independent data (i.e. scientific surveys, ad hoc monitoring programmes, strandings data). Funded by the MAVA Foundation, the project started in 2017, initially focused on Morocco, Tunisia and Turkey. The second phase of the project, initiated in 2020 and due to run until 2022, expanded the geographical scope to include Croatia, Italy, France and Spain, in relation to policy and advocacy activities. The project involves a partnership between the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and contiguous Atlantic area (ACCOBAMS), the General Fisheries Commission for the Mediterranean (GFCM) of the Food and Agriculture Organization of the United Nations (FAO), the Specially Protected Areas Regional Activity Center (SPA/RAC) of the United Nations Environment Programme/Mediterranean Action Plan (UN Environment/MAP), the International Union for Conservation of Nature – Centre for Mediterranean Cooperation (IUCN-Med), BirdLife Europe and Central Asia (BL ECA) and the Mediterranean Association to Save the Sea Turtles (MEDASSET). Life DELFI (LIFE18 NAT/IT/000942) is a five-year (2020–2024) project co-financed by the European Commission under the Life programme, which aims at reducing the interactions between dolphins and fishing activities in Italy and Croatia. The project focuses on bottlenose dolphins (Tursiops truncatus) in the regions of Campanella, Egadi Islands, Tuscany coast (Grosseto area), Aeolian Islands, Tavolara Island, Veneto coast (north of the Po Delta), Torre del Cerrano 9 http://www.fao.org/gfcm/activities/environment-and-conservation/med-bycatch-project/en/ 108 | ICES SCIENTIFIC REPORTS 3:19 | ICES (Abruzzo coast), Central Adriatic (Marche coast), and Istria and Cres in Croatia. The overlap between dolphin distribution and fishing activities in these zones results in high rates of bycatch and depredation events as well as other interactions. The objectives of the project are to reduce the mortality rate of dolphin and limit economic damage suffered by fishers. To do so, the project plans to employ technical solutions related to fishing gears, such as the use of pingers, Bycatch Reducer Devices, alternative gears, and the development of additional economic activities (e.g. dolphin watching development). Post-mortem examinations of dolphins are conducted to assess cause of death, and surveys and interviews are conducted with fishers. 3.4 New tools 3.4.1 Bycatch Risk Assessment (ByRA) Toolbox A new fisheries management tool ("ByRA"10) has been designed for assessing risk of bycatch to endangered and threatened species in data-limited places. ByRA leverages existing information, including local expert knowledge, literature, and field data. Initial development was funded by NOAA's Office of International Affairs to help fisheries in developing countries of Southeast Asia comply with new import regulations from provisions within the Marine Mammal Protection Act. ByRA uses community-driven approaches to generate new insights about areas and seasons of bycatch concern. It combines stakeholder engagement and local expert knowledge with mapbased (geospatial) analyses to highlight potential overlap between the distribution of fishing activities and marine megafauna. For each season and study area, the tool preforms three steps: (1) maps the distribution of fishing activities and marine megafauna species, (2) scores interaction rates, (3) estimates bycatch risk and characterizes data uncertainty. ByRA provides structured spatially explicit information on risks and vulnerabilities that accounts for data and model uncertainty. While few data exist that quantify animals caught in nets and other fishing gears, there are spatial and temporal patterns in bycatch occurrence that can be identified. Maps and summary tables synthesize existing information on data-limited fisheries to inform plans for further research, bycatch mitigation, and species recovery and protection. Outputs also suggest steps to overcome a lack of resources and scientific capacity in-country and guide data collection and monitoring effort. The tool enables planners and managers to establish baselines, identify interventions, and comply with new policy and regulations. Once the underlying data have been collected, risk and data uncertainty maps can be produced and updated very easily. Conversations are underway to apply the tool in more developed sites of the European Union. For example, there is a need to pinpoint high-risk areas within the Bay of Biscay and Baltic Proper for common dolphins and harbour porpoises, respectively. WGMME will discuss potential applications and similar risk assessment approaches under development. Further information is located at https://phys.org/news/2020-09-marine-mammals-valuableframework.html and https://marfisheco.com/contact. 10 The ByRA tool is open source and maintained through the InVEST toolbox by Stanford University: https://naturalcapitalproject.stanford.edu/software/invest ICES | WGMME 2021 | 109 3.4.2 Use of social media as a data source on bycatch The increasing use of social media worldwide over the last decade has encouraged the communication and dissemination of information about the marine environment and the threats it faces, including interactions between marine protected species and fisheries. This fact has been reflected in the growing number of related publications on social media, specially of flagship species such as cetaceans, sea turtles, sharks and seals. Consequently, these platforms are becoming potential databases that researchers are beginning to use for their studies. Usually posts with small pieces of text accompanied by images are published in these websites and the information that can be extracted could be extensive and diverse. Publications about cases of interactions between marine mammals and fisheries can provide information about the species affected, their size and severity of the interaction, as well as details about the fishing gear involved and the type of fishing practice (e.g. recreational, artisanal and industrial fisheries) which can help to identify the origin of the problem and the distribution of the cases. Images can contribute to distinguish the type of interactions (e.g. predation, active bycatch during fishing activities or passive entanglement on abandoned, lost or discarded materials). Lastly, the action of the person who finds each case can be analysed from photos and videos (e.g. direct released or sending to the recovery centre) which can be an indicator of public awareness of the protocols of handling affected species and of the existence of recovery centres in the region. Consequently, knowing the response actions could demonstrate the potential of using these platforms as complementary sources of information and the need to raise awareness of the threat and disseminate the protocols for dealing with these cases. The impact of fisheries on marine megafauna has been investigated using social media, especially to review occurrences of entanglement in marine debris (including fisheries and maritime materials). For example, Parton et al. (2019) reviewed entanglements of sharks and rays worldwide in literature and Twitter, finding that ghost fishing gear was the most common material involved, and that entanglements of eleven elasmobranch species plus numerous records of whale shark entanglements were recorded only in social media. In the Mediterranean, Panayiotou et al. (2020) used Facebook to assess catches of vulnerable shark and teleost fish species by recreational fisheries. Abreo et al. (2019) investigated Facebook content on the impact of marine debris in megafauna in Philippines, identifying ingestion as the most frequent interaction. Pajuelo et al. (2018) studied the occurrence of whale sharks in Peru and their interaction with smallscale gillnet and purse-seine fisheries. The European project INDICIT II (Implementation of the indicator “Impacts of marine litter on sea turtles and biota” in RSC and MSFD areas), within its objective of implementing the indicator “Entanglement in floating debris by sea turtles, birds and cetaceans”, undertook an exhaustive review of publications in social media, distinguishing between passive entanglement in marine debris and active bycatch, as well as extracting details of the materials involved for further investigations about their origin. The report is due to be published. The effectiveness of the assessment and management of fisheries interactions with marine mammals could be enhanced by considering the attitudes of fishers and general public. With this purpose, social media can reveal the perceptions of citizens and their awareness of threats and conservation of marine megafauna. Giovos et al. (2019) studied citizens’ attitudes towards cetaceans over the world and analysed differences among cultures. Claussen et al. (2013) studied the potential of disseminating fisheries sciences on social media. McClain (2019) provided a quantitative assessment of user reactions to images of marine organisms in Facebook; Papworth et al. (2015) reported that only 5% of scientific articles are published in social media and stated that publications about marine mammals with illustrations were more likely to achieve higher diffusion. These studies exemplify the potential of social media to disseminate science progress and results, which can contribute to changes in the perception of protected marine megafauna and 110 | ICES SCIENTIFIC REPORTS 3:19 | ICES to raise awareness among citizens, including fishers. The latter could in turn increase their participation in monitoring and mitigation programs to reduce bycatch following exposure to social media, although the potential of social media to promote stakeholder participation remains to be evaluated critically. Social media can be a source of real-time data and has been used by scientists over the last few years for different purposes regarding conservation of marine mammals. Its use is expected to continue growing (Monkman et al., 2018), although its potential for scientific purposes beyond outreach and education remains to be fully explored and assessed. 3.5 Aquaculture and marine mammals-a Scottish perspective The global marine aquaculture industry is experiencing sustained growth in the face of ongoing consumer demand for seafood products, and this expansion is expected to continue into the future as commercially fished stocks become fully or overexploited (FAO, 2018). Within the ICES area, a wide range of species is under commercial or experimental cultivation. It has long been understood that marine mammals can interact with the aquaculture industry in various ways (e.g. Würsig and Gailey, 2002; Kemper et al., 2003), depending on the species, local environments and business practices involved. The present document aims to summarise the current situation in Scottish waters in terms of existing aquaculture operations and known or suspected interactions with marine mammals, briefly highlighting each type of interaction in turn. The intention is to provide an example framework that may be of use to evaluate marine mammal-aquaculture interactions in other jurisdictions, including those where aquaculture may not (yet) be well established. Scottish aquaculture is currently dominated by Atlantic salmon (Salmo salar), with Scotland being one of the largest global producers (162 817 mt produced in 2016; Scottish Government, 2019). Salmon are typically raised from eggs to juveniles in freshwater sites, and are then transferred to marine grow-out facilities, where they can remain for over one year before being harvested. As of 2018, 221 such sites (hereafter referred to as ‘fish farms’) were active in Scotland, and were heavily concentrated in sheltered waters along western and northern coasts (Scottish Government, 2019; Scotland’s Aquaculture, 2020). Scottish shellfish farming (326 active sites as of 2019; Scotland’s Aquaculture, 2020; Scottish Government, 2020a) is dominated by blue mussel (Mytilus spp.) production, which are typically grown on arrays of vertical ropes close to shore. Both finfish and shellfish aquaculture in Scotland are expected to expand further over the next decade, including into deeper, more exposed offshore waters. Seaweed cultivation, focusing on large brown kelps (Laminaria / Saccharina spp.) is presently in the experimental phase, with considerable potential for expansion; cultivation in Scotland also involves nets or suspended lines seeded with young plants (Campbell et al., 2019). 3.5.1 Direct mortality Depredation of captive fish (mainly salmon) by top predators, particularly seals, has long been identified as a problem within the salmon aquaculture sector, potentially resulting in financial impacts that can be significant (Northridge et al., 2013; Coram et al., 2014). Lethal management (shooting) of both harbour seals (Phoca vitulina) and grey seals seeking to feed on captive salmon has been practiced as a management tool in Scottish finfish aquaculture since the industry was established in the 1970s, to prevent mortality, reduce stress levels among caged fish and prevent fish escapes through net damage (Hawkins, 1985; Northridge et al., 2010; 2013; Coram et al., 2014). Following the adoption of the Marine (Scotland) Act 2010, a licensing system administered by ICES | WGMME 2021 | 111 the Scottish Government was introduced. Under this system, numbers of seals of either species (grey and harbour seals) that could be shot per annum were capped through application of the Potential Biological Removal (PBR) methodology (Scottish Government, 2015; Tett et al., 2018). Since its introduction in 2011, the number of licences awarded to fish farms, and numbers of seals reported shot as a result, have resulted in <200 individuals (of either species) shot per annum, representing <2% of Scottish harbour and grey seal populations; licence applications have declined year-on-year since the scheme was implemented (Scottish Government, 2015; 2020b). Although population-level impacts may be limited, concerns have been raised in relation to welfare aspects (Nunny et al., 2016). On 17/07/2020, in response to updated U.S. government regulations on importing aquaculture products into the US under the US Marine Mammal Protection Act (see Section 3.1.3), the Scottish Government adopted the Animals and Wildlife (Penalties, Protections and Powers) (Scotland) Bill, removing the possibility to shoot seals under licence as a management tool in aquaculture. This decision might in turn encourage development and implementation of non-lethal alternative approaches such as anti-predator netting and acoustic deterrent devices (ADDs), the potential impacts of which on marine mammals has raised other concerns in recent years (see below). 3.5.2 Entanglement Confirmed reports of entanglement of marine mammals in Scottish aquaculture operations (including nets, fishpens and mooring lines) are rare (Tett et al., 2018). There is a single record of a harbour porpoise found bycaught in a salmon farm in 1997 (SMASS, 1997), and a humpback whale (Megaptera novaeangliae) was found trapped underneath a salmon farm in 2014 (SRUC, 2014). While antipredator nets were in apparent widespread use in the early years of the Scottish industry (Hawkins, 1985), their use had declined by the early 21st century due to concerns about e.g. increased difficulty handling the nets, risk of fouling propellers of attending vessels, reductions to water flow through the pens, and the risk of entanglement of marine wildlife (Ross, 1988; Northridge et al., 2010; Coram et al., 2014). It is worth noting that such systems have remained in widespread use in aquaculture settings elsewhere (Canada, Chile, Australia). In recent years, there has been renewed interest in integrating antipredator netting systems into salmon farms (e.g. Shetland News, 2019). Concerns remain about the potential for seals and cetaceans drowning in such antipredator netting systems, or in other forms of aquaculture such as seaweed cultivation (Ross, 1988; Campbell et al., 2019), but there are presently no data to confirm whether this is a problem in Scotland (Coram et al., 2014). 3.5.3 Acoustic impacts Acoustic Deterrent Devices (ADDs) have long been used in Scottish aquaculture in an attempt to deter seals from the vicinity of fish farms (Tett et al., 2018). Various different models are commercially available, each differing in terms of sound output characteristics (intensity, frequency range, duty cycle, etc.). Despite their widespread use and considerable research effort, long-term efficacy of ADDs in deterring seals from fish farms is still unproven (e.g. Götz and Janik, 2013; Coram et al., 2014). At the same time, ADD noise extends well beyond the footprint of individual fish farms (Findlay et al., 2018). This noise has the potential to cause acute and/or chronic impacts on behaviour, distribution and even hearing sensitivity among both target and non-target marine mammal species in inshore Scottish waters, e.g. harbour and grey seals, harbour porpoise, bottlenose dolphin and minke whale (Götz and Janik, 2013; Lepper et al., 2014; Schaffeld et al., 2019). Although probable, there is still a lack of evidence as to whether such repeated exposure to ADD noise can result in hearing damage among individual animals (Coram et al., 2014; Lepper et al., 2014); advances in pathology may allow for further work on this question in future (Morell et al., 2017). 112 | ICES SCIENTIFIC REPORTS 3:19 | ICES Where ADDs have been introduced among naïve marine mammal populations, considerable displacement responses have been observed (e.g. Olesiuk et al., 2002; Brandt et al., 2013). Harbour porpoise in particular have been found to be excluded from areas with ADDs (Mikkelsen et al., 2017). Since their introduction in Scottish salmon aquaculture in the 1990s, local marine mammal populations will have been exposed to increasing ambient noise levels across large parts of western Scottish waters (Findlay et al., 2018), potentially resulting in habituation or redistribution in (i.e. avoidance of) areas of particularly high ADD densities. The use of ADDs in Scotland, and any future licensing schemes to regulate their usage, are presently under review (February 2021). The importance of other sounds produced by fish farms as a by-product of day-to-day operations (e.g. pumps to distribute fish feed, net cleaning, diesel generators, etc.) are as yet poorly understood, although work is ongoing to characterise these outputs in more detail and evaluate potential acoustic impacts. The amounts of noise produced by Scottish shellfish and seaweed farm operations are not well understood at present, although they are likely to be substantially lower than fish farms as they are not staffed on a regular basis. Elsewhere, shellfish spat collection can be accompanied by significant noise pollution (Baltzer et al., 2020). This aspect of shellfish aquaculture requires further investigation in Scotland. 3.5.4 Vessel-based disturbance/collision Fish farms require near-daily visits by staff to ensure high maintenance standards of the captive fish. Their often-remote location requires regular use of company boats, typically fast RHIBs or similar, to transport staff to and from farms. While such traffic can potentially cause disturbance or even collisions with marine mammals, these risks are considered relatively low given the limited numbers of trips per day, and the relative lack of spatial overlap between fish farms and waters frequented by baleen whales (with the exception of minke whales in Scottish waters). Future expansion of the sector into more exposed areas may change this picture. Larger company vessels may visit fish farms every so often e.g. during harvesting or in case of disease outbreaks. Shellfish and seaweed cultivation sites are generally left unattended, significantly reducing associated vessel movements, but disturbance may still occur in some cases (Becker et al., 2011). 3.5.5 Wider ecosystem effects Fish farms can generate waste nutrient discharges, both as solid matter (e.g. faeces, uneaten fish feed) and dissolved nutrients (nitrates and phosphates) that can be consumed by primary producers and scavengers. Wild fish may be attracted to fish farms because of this artificial food subsidy and opportunities for shelter provided by the farm infrastructure (Freon and Dagorn, 2000; Uglem et al., 2014). Such a concentration of wild fish around a fish farm presents a foraging opportunity for marine mammals, but also poses potential risks through e.g. entanglement or exposure to injurious noise levels, if animals remain near farms with ADDs for too long. Little is currently known about the extent to which Scottish aquaculture infrastructure (of any kind) might aggregate wild populations of prey fish and attract marine mammals, although anecdotal observations suggest that species such as seals, harbour porpoise and even minke whales may forage around fish farms. Elsewhere in the world, other species such as bottlenose dolphins are known to engage in this behaviour (which could lead to depredation; Lopez, 2012; Methion and Lopez, 2019) but this has not (yet) been reported in Scotland. Increased levels of fish parasites around farms, and occasional escapes of farmed fish into the environment (Northridge et al., 2010), could also negatively affect prey availability for marine mammals. Indirectly, marine mammals in other parts of the world can be impacted by finfish aquaculture through overexploitation of baitfish as a component of fish feed, although proportions of plant-derived material in feeds have been steadily increasing in recent years (Ytrestøyl et al., 2015; Shepherd et al., 2017). However, Shepherd et al. (2017) estimated that, in 2014, the Scottish salmon sector used ca. ICES | WGMME 2021 | 113 200 000 tonnes of feed, 40% of which was derived from marine sources including fishmeal and fishoils. Much of this would have been imported. Various chemical compounds (chemotherapeutants, feed additives and antifoulants) are discharged as part of aquaculture operations. There is to date no evidence that the chemicals currently used in fish farming in Scotland persist and accumulate in the food chain to the point of affecting marine mammals (Tett et al., 2018). 3.5.6 Conclusion The most obvious direct interaction between aquaculture and marine mammals in Scotland involves attempted depredation by seals on caged fish. Attempts to reduce or eliminate this interaction have resulted in various mitigation measures, some of which (notably ADDs) can have undesirable side effects to other species across larger areas. Management of aquaculture–seal interactions is currently in flux, and likely to change over the near future. The wider ecological significance of aquaculture in Scottish inshore marine ecosystems, including to marine mammals, as yet remains poorly understood. 3.6 Questionnaire on stranding networks in Europe This questionnaire was developed by the International Council for the Exploration of the Sea Working Group on Marine Mammal Ecology (ICES, WGMME) to gain some insight into the potential contribution of European strandings monitoring networks to understanding and quantifying mortality of marine mammals due to fishery bycatch and entanglement. The questionnaire was divided into seven main sections, including some preliminary questions about the respondents and access to data, and 41 numbered questions. Respondents were answered to focus on the year 2019 (if possible) when providing numerical responses. The questionnaire was sent to 49 contacts in strandings networks and related organisations in European countries with Atlantic coasts (including networks from the Atlantic islands of Spain and Portugal and networks from Spain and France which attend strandings on Mediterranean coasts). We received 25 responses, including 22 completed questionnaires. The completed questionnaires came from Belgium, Denmark, France, Germany (2), Iceland, Latvia, the Netherlands (3), Poland, Portugal (3), Spain (5), Sweden and the United Kingdom (2). Responses for Estonia, Faroe Islands and Norway referred to the lack of formal strandings monitoring networks and provided brief details of relevant work on stranded animals. Here, we summarise the responses received. A more detailed analysis will be conducted intersessionally. We also expect to contact respondents again with a request for clarification where responses revealed ambiguity in certain questions or misunderstanding of the information requested, as well as to contact non-respondents. 3.6.1 Data sharing Respondents were asked about the use of questionnaire responses and their views on a future ICES data call. A summary of their responses can be seen in Table 3.6.1. The majority of networks are interested in sharing the information provided through a scientific publication and via the Global Stranding Network. The majority of respondents indicated willingness to participate in writing up of questionnaire responses and expressed positive views towards a hypothetical future ICES data call focused on strandings data. In relation to the latter, some issues were mentioned in the comments, e.g. data should be requested from the regional or national funding body; data were already shared with one or more international organisations, and there was a need for coordination of such data calls; or detailed data could be shared after publication. 120 | ICES SCIENTIFIC REPORTS 3:19 | ICES Financial constraints mentioned included lack of resources to train volunteers, limits on the numbers of animals that could be collected and on the number of necropsies carried out (particularly important if there is a large number of strandings) and the cost of bringing in a pathologist. Issues with human resources, included low availability or absence of volunteers in some parts of a country, lack of personnel to undertake biological analyses (and generally). In relation to the importance of veterinary personnel, one response noted that vets not trained in work on cetaceans may find it difficult to determine bycatch mortality, while trained biologists and veterinarians could do so. Table 3.6.2.6. Limitations to quantify the mortality associated to bycatch from strandings. Type of problem / Importance High Medium Low N/A No reply Total Carcasses often decomposed 7 9 4 0 5 25 Financial resources 7 5 4 4 5 25 Human resources 4 8 3 4 6 25 Issues with carcass recovery 3 4 9 3 6 25 Few carcasses are reported 3 3 11 2 6 25 Issues with carcass examination 2 7 5 4 7 25 Administrative issues 2 5 6 5 7 25 Access to remote areas 2 4 9 4 6 25 Lack of veterinary expertise 2 3 11 5 4 25 No volunteer network 2 3 4 10 6 25 Distribution of volunteers 0 6 4 9 6 25 Logistical issues reported included the advanced state of decomposition of many carcasses; the fact that carcasses reported floating may never reach the shore, and those stranded in the intertidal area may be washed away again; the distribution of competences among different authorities and the occasional failure of local authorities to pass on reports of strandings; denial of access when the beach was crowded; difficulty of access to a few remote areas (especially the difficulty of collecting and examining large whales stranded in remote areas); and, in the case of the Azores, the lack of territorial continuity. Some bycatches are reported directly by fishers and carcasses may be landed for delivery to the strandings network. The extent to which this occurs, varies between countries and between fleets. One respondent reported positive results from initiatives to inform/engage fishers while another indicated that fisher mistrust was an issue of high importance. We note that specific authorisation may be needed to land dead cetaceans as well as to handle them onshore (since they are protected species) and that adverse publicity generated by reports of dead cetaceans being landed may deter fishers and scientists from engaging in such collaborations. One respondent commented that it is not possible to determine bycatch mortality from strandings, presumably referring to the potential use of data on the frequency of bycatch mortality to its importance at population level. We note that strandings (at worst) have a sentinel function and the number of diagnosed bycatch deaths provides a minimum estimate of the number of ICES | WGMME 2021 | 121 animals killed in fishing gear. Furthermore, at least two approaches (based on life tables and drift modelling) could, at least in theory, be used to estimate bycatch mortality at population level, if it were possible to control for various non-trivial biases in the data. 3.6.3 Attending strandings Q10. Procedures for reporting a stranding Most networks receive reports of stranded animals via local authorities and the public (See Table 3.6.3.1). Reporting is mostly via a dedicated phone number. Some networks also receive reports via a dedicated App, a specific website (which may allow upload of reports and photos into an online database), a dedicated e-mail address and/or social media. There may be a designated contact person or institution. Few networks have volunteers actively looking for carcasses. Table 3.6.3.1. Procedures to report strandings to the network. Procedures Yes No Did not reply Total Reporting via local authorities 22 1 2 25 Public reporting to network 20 2 3 25 Dedicated phone number 19 3 3 25 Reporting via social media 10 12 3 25 Use of an App 9 13 3 25 Specific website 9 13 3 25 Volunteers actively look for carcasses 6 16 3 25 Among those networks not using an app, one cited lack of resources as the reason. One respondent mentioned a reduction in use of volunteers for reporting strandings since 1999, with reporting nowadays mostly by members of the public and local authorities, although volunteers are still used when responding to live strandings, mass strandings and periods of high numbers of strandings following a storm. Q11. Who attends; who does what? The majority of networks reported that when necropsies were performed at a specialist facility, they were mostly performed by veterinary pathologists. While post-mortem examination of carcass on site seems to be relatively infrequent, it is usually carried out by a veterinary pathologist or other trained personnel (Table 3.6.3.2). Taking measurements and/or photos, sample collection from carcasses on site, mainly involves other trained personnel although a few networks use untrained personnel or third-party organisations and one network reported that photos and measurements were usually taken by members of the public (Table 3.6.3.3). Some networks reported a flexible approach based on the size and decomposition state of the animal, with volunteers collecting data and samples on site in the case of animals which were unsuitable for transport. A decision about the release of funding for necropsy may depend on the decomposition state. Several networks lack routine access to veterinary / pathology expertise. One network specifically referred to financial limitations on the work they could do. 122 | ICES SCIENTIFIC REPORTS 3:19 | ICES Table 3.6.3.2. Staff in charge of examining the carcass post-mortem on site and performing the necropsy at a specialist facility (Attending: A = Always, U = Usually, S = Sometimes, N = Never. Two respondents selected multiple frequency values, so these answers were counted as “No reply”). Who does what? Post-mortem examination of carcass on site Necropsy at a specialist facility A U S N No reply Total A U S N No reply Total Veterinary pathologist 3 4 7 6 5 25 8 6 2 6 3 25 Other trained personnel 3 3 9 4 6 25 5 3 5 6 6 25 Untrained personnel 0 1 2 13 9 25 0 1 1 15 8 25 Third party organisation 0 0 3 14 8 25 0 0 3 15 7 25 Members of the public 0 0 0 17 8 25 0 0 0 18 7 25 Table 3.6.3.3. Staff in charge of taking measurements and photos of the stranded animal and collecting samples from carcasses on site (Attending: A = Always, U = Usually, S = Sometimes, N = Never. Two respondents selected multiple frequency values, so these answers were counted as “No reply”). Who does what? Take measurements /photos on site Collect samples from carcass on site A U S N No reply Total A U S N No reply Total Veterinary pathologist 1 3 10 5 6 25 2 2 9 6 6 25 Other trained personnel 6 9 2 2 6 25 4 5 7 3 6 25 Untrained personnel 0 2 8 7 8 25 0 1 2 14 8 25 Third party organisation 2 0 7 9 7 25 0 1 6 10 8 25 Members of the public 0 1 7 11 6 25 0 0 1 17 7 25 Q12. The decision process: which animals to attend The decision process is most frequently based on the decomposition state of the carcass (See Table 3.6.3.4). Other factors of high importance are the species (is it considered important and/or is it from an important population or subpopulation). Funding constraints, availability of personnel and the need for representative sampling were reported as being of high importance by between 1/3 and ¼ of networks. Ease of access and specific research questions were reported to be of high importance to fewer networks. One network indicated that live animals (depending on reports) were of high importance. Some respondents also highlighted that the number of stranded animals in their region plays a role in the selection process. For instance, when there are high numbers of strandings in a short time period, it is often not possible to attend them all and, thus, priority is given according to the circumstances. On the other hand, in regions where there are very few strandings yearly, networks attend all stranded animals. ICES | WGMME 2021 | 123 Table 3.6.3.4. Process followed to decide which animals to attend. Decision process High importance Medium importance Low importance No reply Total Decomposition state 13 4 2 6 25 Important species 12 1 4 8 25 Funding constraints 8 3 7 7 25 Availability of personnel 7 5 7 6 25 Representative sampling 6 7 5 7 25 Ease of access 5 7 6 7 25 Specific research questions 4 5 8 8 25 Q13. Indicators of the amount of effort which goes into looking for stranded animals As can be seen in Table 3.6.3.5, very few networks (4/25) reported gathering information on the amount of search effort applied to locate stranded animals. Registering the number of active volunteers or accounting for the density of citizens in an area are the most frequently used measures of effort. Two networks consider the ease of access to the coast and only one has an App to record the kilometres of the coastline which are covered during searching. One respondent mentioned that the characterisation of the effort which goes into looking for stranded animals is currently the subject of specific research projects, and a few respondents mentioned that their area had easily accessible and highly frequented coastlines. Table 3.6.3.5. Information recorded by the stranding networks as a measure of the effort applied looking for stranded animals over their regions. Measure of effort Yes No Did not reply Total Number of active volunteers in an area 3 18 4 25 Density of (human) population 3 18 4 25 Ease of access 2 19 4 25 App to record km of coast covered 1 20 4 25 Volunteers estimate km of coast covered 0 21 4 25 Amount of publicity 0 21 4 25 3.6.4 About the stranded animals Q14. Percentage representation of different species among stranded animals Grey seal is the species reported to be most frequently stranded (23.4% of strandings on average), followed by harbour porpoises (18.9%), common dolphins (12.8%), harbour seals (12.3%), striped dolphins (6.4%) and bottlenose dolphins (3.5%) while the remaining species are all below 3% on average (Figure 3.6.4.1). Evidently, this summary ignores regional differences in the marine mammal fauna (e.g. grey seals and harbour seals are rare visitors in Spain and Portugal). 124 | ICES SCIENTIFIC REPORTS 3:19 | ICES It should be noted that it was not always clear whether non-identified cetaceans and seals (or indeed other taxa) were considered when reporting percentages, and percentages often did not sum to 100%. Animals not identifiable to species can make up a substantial proportion of strandings (e.g. 106 out of 463 cetaceans and five of 16 seals recorded in the Azores). Some networks reported seasonal variation in the species stranded (e.g. in summer more harbour seals and porpoises were reported, while in winter grey seals and other cetaceans were more frequent). Presumably this relates to factors such as life-cycle seasonality (calving, migrations) and the frequency of storms. Some respondents reported an annual increase of strandings of the most common species of up to 10–20% (presumably in the expected reference year, 2019). One respondent remarked that larger marine mammals may be more likely to be reported. Figure 3.6.4.1. Barplot of the averaged frequencies of strandings of the most common species among the respondent regions. Q15. Reported and attended strandings in 2019 (including number of dead animals and those which died/were euthanized) and how many were necropsied. In total, 7487 (average = 416) stranded marine mammals were reported in 2019 by 18 European stranding networks (Table 3.6.4.2). Of those animals, 2968 (average = 247) were attended. Almost 80% (n = 5892) were dead when stranded or died afterwards, and necropsies were performed on 14.9% (n = 876) of the dead animals. Note that the proportion of animals necropsied varied among countries and over time. The “necropsied” category may sometimes have included animals that were sampled but not subject to full necropsy. ICES | WGMME 2021 | 125 Table 3.6.4.2. Summary of the reported, attended, ended up dying and necropsied animals in 2019. Reported Attended Dead/Died Necropsied Sum 7487 2968 5892 876 Average 416 247 368 52 Maximum 2282 1791 2181 144 Minimum 11 2 1 0 Q16. Important patterns or trend in numbers of stranded marine mammals recently Twenty networks replied to this question, of which 16 reported having detected patterns or trends in numbers of stranded marine mammals recently. Four networks did not detect any patterns or trends, in one case due to its recent creation. Most respondents reported changes over time in the numbers of strandings of several species. Some reported changes in seasonal patterns or an increase in the frequency of Unusual Mortality Events and mass strandings events. A few networks mentioned that some of the mortalities were linked to epizootic events. One network hypothesized that the shifts in distribution of strandings of some species could reflect responses to climate change. Q17. Live strandings and euthanized animals Among the 15 stranding networks which provided information, on average only a small proportion of cetaceans stranded alive (11.0% ranging from 0.5% to 40.5%), of which 79.7% (range <1% to 100%) died or were euthanized. In comparison, 44.2% (range 1% to 80%) of seals stranded alive of which on average 27.8% (range 1% to 55%) died or were euthanized. The overall picture disguises wide regional variation. It should be borne in mind that the term “live stranding” maybe misleading for seals, since some animals reported may simply have been hauled out (a point made by one respondent who did not report on live strandings of pinnipeds). Six networks reported that other organisations hold or might hold information about live strandings. Five networks mentioned that some live stranded animals go into rehabilitation. A few networks indicated that some of the live stranded animals were refloated. One network indicated that data gathered on harbour porpoises were passed to another network. Q18. How frequent are large mass strandings (events involving ten or more animals)? Eleven networks reported mass strandings (≥ 10 animals) in their areas during the course of their activity. Sperm whales (5/11) and pilot whales (short and long-finned combined; 5/11) were the most commonly reported, followed by common dolphins (3/11) and beaked whales (2/11). The other species involved (reported once each) were grey seals, harbour seals, Fraser’s dolphins, Risso’s dolphins, and false killer whales. In addition, two networks indicated that they recorded several stranding events involving between 2–9 individuals of common dolphin, bottlenose dolphin, striped dolphin, spinner dolphin and pygmy sperm whale. Five networks indicated that they had never recorded mass strandings. One commented that the definition of a mass stranding was ambiguous, and should consider not only the number of individuals but also the timing of the strandings. This network recorded strandings of more than ten harbour porpoises at the same approximate location over a couple of days. In relation to the definition of mass stranding, Iceland did not mention beaked whale mass strandings, but there 126 | ICES SCIENTIFIC REPORTS 3:19 | ICES was an Unusual Mortality Event in 2018 (Grove et al., 2020). Similar events seem to have happened previously with approximately decadal frequency (Halldórsson et al., 2019). Six networks did not reply to the question. One of these networks provided a short note on the unusually high frequency of cetacean strandings between 28th March–2nd May 2020. We may need to revise this question to allow inclusion of unusual mortality events in which multiple animals strand over an extended area over several days. 3.6.5 Processing stranded animals Q19. Data and samples collected from dead stranded marine mammals Most metadata are collected on all stranded animals (whether necropsied, sampled but not necropsied or only recorded with no sampling or necropsy), as seen from Table 3.6.5.1. Information on body condition (i.e. girth, weight, body condition code, and blubber thickness) is rarely taken on animals that are only sampled or recorded. Samples are mainly collected on necropsied animals. Table 3.6.5.1. Summary about the data and samples collected from dead stranded animals during their necropsy, sampling and recording. Data or sample Which animals? No reply Total Necropsied Sampled Recorded Location 19 16 20 4 25 Date 18 16 20 4 25 Species 18 16 19 5 25 Sex 17 15 17 5 25 Length 17 16 14 5 25 Girth 17 5 2 6 25 Blubber thickness 18 9 0 6 25 Weight 16 3 2 8 25 Decomposition code 17 13 15 5 25 Body condition code 16 6 3 8 25 Photograph 19 16 20 4 25 External bycatch signs 18 12 10 6 25 Teeth 18 10 1 6 25 Skin 18 11 3 5 25 Blubber 18 10 3 5 25 Ovaries or testes 18 4 1 6 25 Foetus (if present) 18 4 1 6 25 Stomach contents 18 6 1 5 25 Liver, kidney 18 5 0 6 25 ICES | WGMME 2021 | 127 A few networks reported collecting other types of samples (e.g. muscles, serum, bone material, central nervous system, spleen). Three networks provided information on samples they collect but did not specify whether any samples are taken from animals which are not necropsied. One network specified that “sampled” animals were those whose decomposition state was too advanced to perform a full necropsy (which was our assumption). One network pointed out that the information on weight is only a rough estimate if animals are not necropsied. One network which did not complete the table commented that, due to the high number of dead animals they receive, the information collected and stored in their database is restricted to sex, length (sometimes) and photographs. Q20. Photos of strandings and their use to diagnose bycatch The majority of the stranded animals are photographed (on average over 85%; some respondents indicated that “>X%” of stranded animals were photographed, so calculations are not exact) and the images are archived. However, there was also considerable variation between countries: some networks take photos of every stranded animal, others photograph as few as 10% of animals. On average, around one quarter (again the figure is not exact) of the collected photos were considered suitable for detecting evidence of bycatch but the percentages reported ranged from 0 to 100%. Some respondents mentioned that even though bycatch evidence can sometimes be detected from photos, more cases are diagnosed from veterinary examination. The main signs considered as evidence of bycatch were if a fishing net appeared in the picture or if there were external marks consistent with entanglement/entrapment. The type of photos considered suitable for detecting bycatch signs varied. Some networks use only photos taken during necropsy, others use all photos taken by network staff, while others would use images sent by citizens. Evidently, while photos can provide positive evidence of bycatch mortality, they can rarely confirm that animals were not bycaught. The “Regional Bycatch Evaluation Evidence Programme (BEEP)”, carried out in Cornwall (UK) by the Cornwall Wildlife Trust Marine Strandings Network (CWTMSN, part of the UK’s CSIP consortium) includes the use of photos to determine bycatch. Q21. Analyses carried out on samples collected from stranded animals Determination of female reproductive status and of maturity state in general were the most frequently reported routine analyses (carried out routinely by over half the networks which responded) (See Table 3.6.5.2). Surprisingly, only three networks reported that age was routinely determined for stranded cetaceans. Nevertheless, most of the networks which responded carried out such analysis either on a routine or ad hoc basis. Table 3.6.5.2. Frequency of analysis about reproductive status, maturity state, diet and age from stranded animals. Analysis Routine Ad hoc Never No reply or NA Total Female reproductive status (e.g. pregnant, lactating) 11 7 1 6 25 Maturity state 10 7 1 7 25 Diet (e.g. stomach contents) 9 10 0 6 25 Male reproductive status 7 10 1 7 25 Age determination 3 13 3 6 25 128 | ICES SCIENTIFIC REPORTS 3:19 | ICES One of the respondents, from a country which does not have a stranding network (and for which the answer is therefore considered not applicable), reported collecting information on diet, age, and reproduction. Some networks commented that samples are stored in anticipation of future research projects, increased availability of personnel and/or dedicated funding. It was also mentioned that results from samples sent out for analysis are not always reported back to the network. Regarding age determination, although counting growth layer groups in sections of teeth is the usual approach (e.g. Read et al., 2010), some networks mentioned using the protocol developed by Calzada et al. (1997) for specific dolphin species, i.e. based on the degree of fusion of ephiphysial plates or the hyoid complex as revealed by means of X-ray examination. Few stranding networks reported examining ovaries with binocular magnifiers to detect a corpus luteum and/or corpora albicantia in order to assess female reproductive status. Q22. Decomposition states of the stranded animals In general, a low percentage of marine mammals strand alive (average 6.5%, range <1% to 25%. Note that the responses to this question are not entirely consistent with responses to Q17). Over one third of the strandings are individuals in an advanced state of decomposition (average 37.3%, range 12% to 85%. In 18.0% of cases on average (range 0% to 67%), the decomposition state is not determined (Figure 3.6.5.1). Figure 15.6.5.1. Percentage of the decomposition status of the stranded marine mammals reported by 14 stranding networks (average values). The fifth category “Indeterminate” seems to be treated slightly differently among the stranding networks. In some cases, the category “Indeterminate” included cases from which only bones remain, cases in which the state could not be determined. Q23. Dietary preferences and evidence of feeding in or around fishing gear Many stranding networks have collaborated in or carried out some diet analysis. Few references were provided about the published information from the samples collected. Some regions reported that the diet varies depending on the species, season and region. Information on the main prey of several cetacean and pinniped species is summarised in Table 3.6.5.3 below. ICES | WGMME 2021 | 129 Table 3.6.5.3. List of the most common prey species of some common marine mammal species stranded over the respondent regions. Predator species Prey species Common dolphin anchovies, pilchards, sardine, chub mackerel, horse mackerel Striped dolphin cephalopods Bottlenose dolphin hake, conger eel, Liza spp., blue whiting Porpoise sand gobies, whiting, herring, sprat, cod, sandeels Harbour seals herring, garfish, plaice and dover sole Grey seals armed bullhead, whiting, dab, sandeels, cod, roach, dover sole Evidence of animals feeding in or around fishing gear was reported, such as cases of seals which had drowned, had fish lodged in the oesophagus or had a piece of net in the mouth. Cetaceans with fragments of nets in their digestive system/mouth, stomachs full of intact prey or net marks in the body, and animals (e.g. bottlenose dolphins) seen feeding near/on fishing gear by fishery observers were reported. It is more common to find evidence of grey seals feeding in or around fishing equipment than it is for porpoises. 3.6.6 Necropsies Q24. The decision process: selecting carcasses for necropsy As was the case for decisions about attending strandings, most networks reported basing decisions about which animals should be necropsied on the decomposition state (See Table 3.6.6.1). Similarly, the second most important factor was whether the stranding involved an important species or population. For instance, some networks specified that harbour porpoises (from the Baltic Sea and Galicia (NW Spain)), bottlenose dolphins (Galicia) or narwhals would be prioritised (regardless of the decomposition state of the animal). Other relevant factors included funding constraints (e.g. funding for a fixed number of necropsies), ease of access, the need for representative sampling and specific research questions. Availability of personnel and the body size of the cetacean were more rarely considered as limiting factors. Table 3.6.6.1. Key factors to decide which animals will be necropsied. Decision process Yes No No reply Total Decomposition state 15 3 7 25 Important species 11 7 7 25 Funding constraints (fixed numbers) 9 9 7 25 Ease of access 8 10 7 25 Representative sampling 7 11 7 25 Specific research questions 7 11 7 25 Availability of personnel 5 13 7 25 Body size (ease of transport) 4 14 7 25 136 | ICES SCIENTIFIC REPORTS 3:19 | ICES Twelve networks reported that static gears had been identified as causing marine mammal bycatch mortality, including several types of gillnets (i.e. codnets, trammelnets, bottom-set gillnets, single walled gillnets, static tanglenets, passive monofilament type gear). Three networks reported various traps and pots being involved in marine mammal bycatch and/or entanglement (i.e. creel fishing, recreational fykenets on the beach, and other large fish traps). Five networks reported towed or floating gears to be involved in bycatch mortality, which included trawlers (e.g. pelagic pair trawls, high vertical opening bottom trawls) and purse seine. One network mentioned that although marine mammals were caught by trawlers, there was no evidence that the animals died in the trawling nets and it is believed that these animals were already dead when fished. In Macaronesia, one network (Azores) reported the pole and line fishery being the cause of mortality of a neglectable number of animals. Another network (Canaries) reported the tuna fishery being involved in bycatch mortality. Information on the gears involved comes from a variety of sources. Two networks indicated that the information they provided on the gears and fisheries likely involved in marine mammal bycatch mortality was based on the overlap of the likely areas of bycatch (based on drift modelling of the origins of stranded carcases) with fishing effort (from AIS or VMS data). Two networks mentioned using information from at-sea monitoring and one mentioned logbook data provided by fishers. Some networks mentioned diagnosis during necropsy, including identification of net marks as well as remains of gear on carcases. One network mentioned that remains of gear were found around the neck of a number of seals that survived bycatch in 2021. Other evidence included personal observations, witness accounts and photographs. We may need to repeat this question, providing more structure in relation to the fisheries involved, species caught and the means by which the fishery or gear was identified. Q38. Reporting of bycatch/entanglement data to other organizations The majority of networks report to their national government, to IWC and to ASCOBANS (see Table 3.6.7.2). One network specified that the annual reporting to their government including bimonthly reports during the strandings peak season. Two networks report to their regional governments, one on a monthly basis and the other annually. One network indicated delivering once per year their full database to the local government. Networks in two countries also report to HELCOM; one mentioned doing so annually for seals and porpoises. One country reports information on all mammals annually to NAMMCO. One network reports to the European Commission every six years, under the Habitats Directive and Marine Strategy Framework Directive. Four networks report to ICES (two of which specified that this was to WGBYC. We note that most countries report under the Habitats Directive, provide information to ASCOBANS and IWC, and respond to ICES data calls linked to WGBYC, but only some of these countries delegate these tasks to national strandings networks. The quality of data provided to IWC, and to a lesser extent to ASCOBANS varies markedly between countries (personal observation) and there is evidently scope to both coordinate reporting of strandings data (to reduce duplication of effort) and to devise a standardised common format (bearing in mind the different reporting cycles of different organizations). ICES | WGMME 2021 | 137 Table 3.6.7.13. Organizations and frequency to which bycatch/entanglement information is reported by the networks. Organization Reporting Report frequency (if reporting) Yes No No reply Annually Other* No reply National government 16 5 4 13 2 1 IWC 13 8 4 10 2 1 ASCOBANS 11 10 4 6 3 2 Other*: Other reporting frequencies to ASCOBANS include “Cfr ASCOBANS requirements”, “Once per triennium”, “Upon request”. Other reporting frequencies to IWC include “Just once”, “Upon request”. Other reporting frequencies to National governments include “Annually, quarterly and ad hoc”, “Irregular”. Q39. Collaboration with fishers to obtain information on cetacean bycatch Most networks that replied to this question are currently collaborating with fishers to obtain information on cetacean bycatch (See Table 3.6.7.3). They record cetacean bycatches reported by fishers and fishers also submit known bycatch cases for necropsy. One network indicated that although they do not currently receive carcasses, previously one fisher regularly reported catches and provided dead animals. Half of the networks that replied reported that known bycatch cases submitted for necropsy by fishers are treated separately from the strandings cases. This obviously becomes relevant when assessing the importance of bycatch based on strandings data. Ten networks work with fishers to disentangle/release live bycaught animals. One network pointed out that other actors (i.e. the coastguards) are engaged in the release of live captures in recreational nets. Table 3.6.14.3. Summary of the collaboration of the networks with fishers to gather information on cetacean bycatch. Collaboration with fishers Yes No No reply Total Do you record cetacean bycatches reported by fishers? 12 5 8* 25 Are any known bycatch cases submitted for necropsy by fishers? 12 7 6 25 If so, do you treat such records/carcasses separately from strandings? 8 8 9 25 Do you work with fishers to disentangle/release live bycaught animals? 7 10 8 25 Is there a carcass tagging programme for bycaught cetaceans? 2 15 8 25 Only two networks reported currently having a carcass tagging programme for bycaught cetaceans. One of these indicated that 8–40% of tagged carcasses that were predicted to strand were indeed reported stranded. The other network reported that 26.7% of the tagged carcasses reached the shore. A third network indicated that a tagging programme was implemented in the past but that no animals were tagged during the course of the programme. One network indicated that tagging programmes are conducted by other organisations in their country. 138 | ICES SCIENTIFIC REPORTS 3:19 | ICES Q40. Evidence of marine mammals interacting with aquaculture installations Eighteen networks replied to the question. Six respondents indicated not having encountered evidence of marine mammals interacting with aquaculture installations. Two networks indicated they did not know about such interactions. Ten networks reported some sort of interactions, involving both cetaceans and seals. The interactions reported included animals seen in the vicinity of aquaculture installations, in some cases staying in the area for months. In some regions, dolphins were seen close to the floating cages, and entering into delimited protected areas for fish, mussel cages, longlines and tuna traps. Marine mammals are also suspected to feed on fish that are accidentally released from the aquaculture installations. Some species take advantages of mussel cultivation rafts to catch fish. Cases of entanglement include the entrapment of common dolphins in oyster rearing installations (tables), the entanglement of a humpback calf in an aquaculture net, and the entanglement of a bottlenose dolphin in a net. Some networks reported cases of depredation. Some governments have authorised licences for shooting seals to deal with depredation issues, which has led to shot seals being sent to the stranding networks. 3.6.8 General comments by respondents A few respondents indicated having ongoing projects to improve the monitoring and attendance of strandings in their areas, and they are therefore expecting to have more information on strandings and necropsies in the near future. Some differences between networks are apparent in relation to the determination of bycatch cases. For example, one network commented that they only are able to determine bycatch mortality from necropsied animals although good quality photos could help to detect signs of net entanglement. Some respondents commented on the utility of the questionnaire and the necessity of gathering information about the state, capacity and limitations of stranding networks. For example, they recommended the addition of questions on the assessment of the quality of examinations and interpretations. It appears that more effort may be needed to ensure the application of common standards and protocols where it is practical to do so. Certainly, it is essential that metadata allow an end-user to distinguish datasets derived using different approaches. However, the work done by strandings monitoring networks which (for example) do not have access to a veterinary pathologist should not be undervalued. In general, as well as providing valuable data, the involvement of NGOs and citizen scientists helps achieve conservation goals by encouraging public engagement. It was also suggested that WGMME should increase efforts to coordinate work with WGBYC regarding information on bycatch evidence extracted from stranding data. The authors note that both groups are following an ICES Roadmap on cetacean bycatch and, in relation to strandings data, procedures are still being developed. The present exercise is part of the process. 3.7 References Abreo, N. A. S., Thompson, K. F., Arabejo, G. F. P., and Superio, M. D. A. 2019. Social media as a novel source of data on the impact of marine litter on megafauna: The Philippines as a case study. Marine Pollution Bulletin, 140, 51–59. https://doi.org/10.1016/j.marpolbul.2019.01.030. ICES | WGMME 2021 | 139 Arbelo, M., de los Monteros, A.E., Herráez, P., Andrada, M., Sierra, E., Rodríguez, F., et al. 2013. 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