Cephalopods in Greenland Waters. Technical Report No. 57

CEPHALOPODS IN GREENLAND WATERS Technical report no. 57, 2004 Pinngortitaleriffik, Greenland Institute of Natural Resources 2 Title: Cephalopods in Greenland Waters Authors: Rikke Petri Frandsen & Kai Wieland Serial title and number: Technical report no. 57 Publisher: Pinngortitaleriffik, Greenland Institute of Natural Resources Date of publication: 1st July 2004 Translation: Emma Kristensen Cover photo: Female Bathypolypus sp. caught in a bottom trawl off West Greenland in July 2003. Foto: R.P. Frandsen ISBN: 87-91214-09-2 ISSN: 1397-3657 Cited as: Frandsen and Wieland 2004, Cephalopods in Greenland Waters. Technical report no. 57, Pinngortitaleriffik, Greenland Institute of Natural Resources Contact address: The report is only available in electronic format. You can download a PDF-file of the report at this homepage http://www.natur.gl/publikationer/tekniske rapporter It is possible to achieve a print of the report here: Pinngortitaleriffik, Greenland Institute of Natural Resources P.O. Box 570 3900 Nuuk Greenland Phone: +299 32 10 95 Fax: +299 32 59 57 E-mail: [email protected] www.natur.gl Cephalopods in Greenland Waters by Rikke Petri Frandsen and Kai Wieland 3 Technical report no. 57, 2004 Pinngortitaleriffik, Greenland Institute of Natural Resources Eqikkaaneq Kalaallit Nunaata imartaani amikut assigiinngitsut 15 nassaassaapput. Ilimagineqarpoq amikut ilaat Gonatus fabricii naammattuugassaanerusoq. Nassaassanera aammalu lipid-inik akoqarluarnera peqqutaaqataalluni siusinnerusukkut oqaatigineqarnikuuvoq amikoq taanna tunisassiassatut soqutiginaateqarsinnaasoq. Kalaallit Nunaat avataaniit amikunik 800 tonsit missaannik eqqussuisarpoq, taakkulu qaleralinniarnermi (Rheinhardtius hippoglossoides) saattuarniarnermilu (Chionoecetes opilio) neqitassatut atorneqartarlutik. Kalaallit Nunaani tunisassiassanik amikorniarnernik nalunaarsuisoqarnikuunngilaq, kisiannili naluneqanngilaq raajarniarnermi amikut pisarisoorneqartartut neqitassiassatut toqqorneqartartut (Olsvig aamma Mosbech 2003). Imartani assigiinngitsuni qalunik naqqarsiutinik atorluni misissuisarnerni paasineqarnikuuvoq amikut amerlanerpaat Qeqertarsuup eqqaani 400 aamma 600 meterit akornanni itissutsini nassaassaanerusut. G. fabricii immap ikerani nassaassaaneruvoq, inerissimasortai itissutsini 400 aamma 1100 meter-it akornanni naammattuugassaallutik. Misissuinerit tamarmik qalut naqqarsiutit atorlugit misissuinerupput, taamaattumillu amikut G. fabricii-t immap ikeraniinerusoq uumasuusut pisaqarfiunnginnerunissaat ilimagineqarsinnaalluni. 600 meteriniit itinerusuni misissuinerit ikittuinnaasimapput, taamaattumillu amikut G. fabricii-t misissuinernit paasisaniit immap ikerinnaasiornerunissaat aammalu siammarsimanerunissaat ilimagineqarpoq. Amikut pingaartumillu Gonatus sp.-t immami uumassuseqarnermut pingaaruteqartorujussuupput, tassami aalisakkanit allanit, imaani timmissanit kiisalu imaani miluumasunit nerineqarluartarmata. Amikut iluaqutiginiarneqassappata imaani uumassuseqarneq piujuartitsinissarlu ataqqillugit pilersaarusiortoqartariaqarpoq. 4 Sammenfatning Mindst 15 forskellige blæksprutter lever i Grønlandsk farvand. Det antages at Gonatus fabricii er den hyppigst forekomne art og på baggrund af dens forekomst og høje indhold af lipider, har det tidligere været fremsat, at arten kunne være af kommerciel interesse. Grønland importerer ca. 800 tons blæksprutter, der bruges som agn til fiskeri efter hellefisk (Rheinhardtius hippoglossoides) og krabber (Chionoecetes opilio). Der er ikke registreret kommercielt fiskeri efter blæksprutter i Grønland, men lokalt bliver bifangst af blæksprutte i rejefiskeriet gemt og anvendt som agn (Olsvig og Mosbech 2003). Togter med bundtrawl har vist, at de største koncentrationer af blæksprutter findes i Diskobugten på dybder mellem 400 og 600 m. G. fabricii har en oceanisk udbredelse, og de voksne individer befinder sig midt i vandsøjlen på dybder mellem 400 og 1100 meter. Alle undersøgelser er udført med bundtrawl og må derfor forventes at have en begrænset fangst af pelagiske (fritsvømmende) arter som G. fabricii. Da der desuden kun har været få undersøgelser af områder dybere end 600 m, antages det at den egentlige udbredelse af fx G. fabricii er mere vidtstrakt, end det fremgår af undersøgelserne. Blæksprutter generelt og i særdeleshed Gonatus sp. har en meget vigtig rolle i økosystemet da de udgør en essentiel andel af føden for fisk, havfugle og marine pattedyr. En udnyttelse af ressourcen skal derfor tilrettelægges med respekt for bæredygtigheden af hele økosystemet. Summary Greenland waters are inhabited by at least 15 species of cephalopods of which one, Gonatus fabricii, is most commonly caught. Due to its abundance and lipid content, it has previously been stated that this species could be of commercial interest. In Greenland approximately 800 tons of squid are imported and used as bait in the long line and trap fishery for Greenland halibut (Rheinhardtius hippoglossoides) and snow crab (Chionoecetes opilio), respectively. There is no record of any commercial fishery on cephalopods in Greenland waters, but locally, the by-catch of squid in the shrimp fishery is kept and used as bait (Olsvig and Mosbech 2003). The highest concentrations of cephalopods as registered from bottom trawl survey, have been found in Disko Bay at depths of 400-600 m. G. fabricii is oceanic and adults live in midwater at depths ranging from 400 to 1100 m. The surveys are conducted with bottom trawls and only few investigations have been carried out at depth below 600 m. The true distribution of pelagic species as Gonatus sp. is thus expected to exceed findings in the surveys. The ecological importance of cephalopods in general and Gonatus sp. in particular is profound, since they constitute a significant element of the diet of fish, sea birds and marine mammals. An exploitation of the resource should respect the carrying capacity of the entire ecosystem. 5 6 Table of Contents Eqikkaaneq .........................................................................................4 Sammenfatning..................................................................................5 Summary.............................................................................................5 Table of Contents...............................................................................6 Introduction........................................................................................7 Investigations on cephalopods in Greenland waters.................................................................. 7 Distribution of cephalopods in Greenland waters ...................................................................... 8 Cephalopod species in Greenland waters....................................10 Cirrate octopods (Cirrata)............................................................................................................. 10 Incirrate octopods (Incirrata)........................................................................................................ 10 Squids (Teuthida)........................................................................................................................... 11 Bobtail squids (Sepiolida) ............................................................................................................. 12 Review of literature on Gonatus sp................................................13 Distribution..................................................................................................................................... 13 Biology............................................................................................................................................. 14 Biomass............................................................................................................................................ 14 Ecological importance ................................................................................................................... 14 Marine mammals as predators on Gonatus sp. .......................................................................... 15 Fisheries........................................................................................................................................... 16 Assessment...................................................................................................................................... 16 Conclusion........................................................................................17 Acknowledgements.........................................................................17 References.........................................................................................18 Introduction Investigations on cephalopods in Greenland waters Distribution of the early life stages of Gonatus fabricii in Greenland waters was investigated sporadically in the 1980’s and early 1990’s. Since then, no investigations had cephalopods as target. 7 Fig. 1: Map showing NAFO and ICES divisions in Greenland waters (The 200 m isobath is indicated by the dotted line). This report presents recent information on cephalopods in Greenland waters based on the literature and on by-catch data from research surveys conducted in East and West Greenland waters in recent years (Fig. 1). Results from trawl catches from annual shrimp and two different types of ground fish surveys were considered in the analysis: The Greenland Institute of Natural Resources (GINR) bottom trawl survey for northern shrimp (Pandalus borealis) at West Greenland: The gear used is a shrimp trawl with a high vertical opening (10–12 m), which is towed at 2-3 knots. The survey is conducted from July to October and covers the offshore area of West Greenland between 59◦00’N and 72◦30’N and depths between 150 and 600 m. In addition, the Disko Bay is covered and in 1992 to 1996 an area off East Greenland was investigated as well. From 1992 and onwards, catch in weight and in number have been registered for all cephalopod species pooled (i.e. without detailed taxonomic identification). The Institute for Sea Fisheries Hamburg (ISH) ground fish survey for cod (Gadus morhua) at East and West Greenland: The survey covered, in recent years, NAFO subdivisions 1C-1F and ICES division 14 at depths down to 400m. The survey gear is a ground fish trawl with a vertical opening of 3–4 m, which is towed at 4.5 knots. In addition, a pelagic trawl was used on one station off Southeast Greenland in 1999 and in 2002 (sampling depth 680-705 m) . Data on cephalopods from 1999 and 2002 were available from Zumholz and Piatkowski (unpubl.). The Greenland Institute of Natural Resources ground fish surveys for Greenland halibut (Rheinhardtius hippoglossoides) at East and West Greenland: The gear used is a bottom trawl, towed with 3 knots. Catches both in weight and in number are registered for the total combined cephalopod catch. Off West Greenland, this survey covers areas with depths of 200 to1400 m. Noteworthy is, that none of the surveys are ideal for cephalopod sampling, thus catchabilities of the treated species are unknown. Hence the results are likely to be highly biased by gear type, towing speed and depth range of the surveys. Distribution of cephalopods based on these surveys should therefore be interpreted with caution. Distribution of cephalopods in Greenland waters Density of cephalopods has been calculated from the shrimp and the ground fish surveys conducted by the GINR in 1992-2002 and 1997-2002 respectively. The results indicate that the highest cephalopod densities (kg km-2) off West Greenland are found in Disko Bay and in the deep trenches between Disko Bank, Store Hellefiske Bank and Lille Hellefiske Bank. Furthermore, high densities occurred in offshore areas north of 62º30’N (Fig. 2). 8 Fig. 2: Distribution of cephalopods in Greenland waters (Data from the GINR shrimp and ground fish surveys conducted in 2001). 60°45' 62°30' 64° 15' 66°15' 1C 1D 1B 1A 1E 1F 68°50' 14 GREENLAND Cephalopod catches in 2001 (kg/sq.km ) Shrimp survey 50 to 100 (3) 10 to 50 (21) 5 to 10 (23) 1 to 5 (75) 0 to 1 (123) Ground fish survey 100 to 500 (10) 50 to 100 (10) 10 to 50 (31) 5 to 10 (13) 1 to 5 (46) 0 to 1 (106) Variation between years is small and the distribution in 2001 is presented as representative for the investigated period (Fig. 2). In all GINR surveys off East Greenland, cephalopod catches have been extremely low. In 2001, no survey was conducted in East Greenland. Cephalopods were caught throughout the investigated area and densities are increasing with depth. Based on personal observations, we believe that off West Greenland, by weight, the majority of the cephalopod catches in the shrimp survey is Gonatus fabricii whereas Cirrate 9 octopods are dominating in the GINR ground fish survey. Whether this difference is due to depth, gear or geography is unknown. Kristensen (1984) reported that the most common squid in Greenland waters is Gonatus fabricii. The adult population of this species is pelagic and usually found at depths of 1000 m and deeper (Bjørke and Gjøsæter 1998). As the catchability of pelagic species must be very low in bottom trawl surveys, the true offshore distribution of cephalopods is expected to be more widespread. Results from shrimp surveys, indicate that mean individual weight of cephalopods, peaks at bottom depths between 400 and 600 m in Disko Bay (68.33 ± 3.34 g) (Table 1). For G. fabricii, mean individual weights of approximately 10 g and 200 g would correspond to pen1 lengths of 6 and 20 cm and ages of 7 months and 2 years, respectively (Kristensen 1984). Equally, and assuming that the entire cephalopod catch in Disko Bay is G. fabricii, mean pen length at depths between 400-600 m would be 13 cm and average age, 1 year. However, during the shrimp survey in 2003 only few individuals with a length above 15 cm has been caught. Table 1: Weight (Mean ± SE)(g) of cephalopods caught in GINR shrimp surveys. Stations where cephalopods were caught have been divided into strata based on depth and area. Note that ICES area 14 (East Greenland) was only investigated in 1992-1996. Figures in brackets indicate number of stations in the stratum. 150-200 m 200-400 m 400-600 m NAFO 1A (excl Disko Bay) 22.28 ± 1.80 (51) 22.16 ± 1.35 (267) 32.67 ± 2.70 (70) NAFO 1B (excl Disko Bay) 17.25 ± 2.49 (126) 25.31 ± 6.00 (452) 25.50 ± 1.89 (132) NAFO 1C 13.45 ± 1.41 (103) 13.68 ± 1.04 (103) 26.97 ± 8.00 (54) NAFO 1D 12.35 ± 1.70 (68) 15.03 ± 1.37 (73) 16.27 ± 3.31 (16) NAFO 1E 28.11 ± 15.97 (46) 19.28 ± 9.30 (52) 6.92 ± 1.84 (8) NAFO 1F 11.02 ± 1.22 (58) 17.13 ± 3.13 (46) 9.97 ± 1.21 (35) ICES 14 28.97 ± 8.92 (13) 22.27 ± 2.67 (83) 19.47 ± 3.35 (33) DISKO BAY 28.04 ± 4.25 (13) 54.01 ± 4.11 (148) 68.33 ± 3.34 (126) 1 The pen (=gladius) is a feather or rod shaped chitinous supporting structure in the dorsal midline of some families of squid. 16 Results from stomachs and intestines of seals in the Greenland Sea, off East Greenland, indicate that G. fabricii is the dominant food item for hooded seal (Cystophora cristata) but not for harp seal (Phoca groenlandica) in this area (Potelov et al. 2000). Off West Greenland, harp seal did contain remains of squid though (Kapel and Angantyr 1989, Potelov et al. 2000). A study on stomachs of ringed seal (Phoca hispida) from West Greenland shows that G. fabricii is included in the diet in all samples except those from the northern most municipalities. Thus from Upernavik in the north to Nanortalik in the south, ringed seal feed on G. fabricii. The estimated fraction by weight peaks in Uummannaq and Kangaatsiaq with 52.5% and 45.8% respectively (Siegstad et al. 1998). Fisheries There is no history of fishery directed towards cephalopods in Greenland waters, but based on the high occurrences of early life stages of G. fabricii off West Greenland, Piatkowski and Wieland (1993) suggested that the species might be of commercial interest. As previously mentioned, Bjørke and Gjøsæter (1998) estimated the lifetime biomass production of G. fabricii in the Norwegian Sea, to be 20 mill t. Of this biomass, the authors calculated that sperm whales consume 384 750 t/year and northern bottlenose whales consume 480 000 t/year. Furthermore it is reasonable to believe that at least 100 000 t of G. fabricii is consumed by hooded seal in this area (Bjørke 2001). Based on these calculations Bjørke and Gjøsæter (1998) suggest that there is a surplus production of G. fabricii taking place in the Norwegian Sea, which could be exploited by the fisheries. In short lived species, abundance may fluctuate widely from year to year, so that predators and fisheries must be able to turn to alternative resources in years of low abundance (Piatkowski et al. 2001). In 2003, an experimental bottom trawl fishery for cephalopods was conducted off West Greenland during a period of two months. In this experimental fishery, the total catch of Oegopsids (probably Gonatus sp.) was 4.7 kg. In 1998, a pelagic trawl was used in an experimental fishery targeting adult G. fabricii in the Norwegian Sea. Catches were small (max. 10 kg haul-1) probably due to the slow speed of the trawl (1.5 knots) (H. Bjørke pers. comm.). There are no other reports on catches of large specimens of Gonatus, thus its commercial value is yet to be investigated. Assessment In short-lived and fast growing species such as squid, the standing stock (biomass) per se is not necessarily a good indicator of the level of predation or exploitation that the population may sustain, since the rate at which biomass is generated must also be considered. Thus, catch statistics per month rather than per year, is necessary for cephalopod stock assessment (ICES 2003). The influence of environmental factors on cephalopod stocks in Greenland is unknown but likely to be of high importance. From the fishery for squids (Loligo sp.) in the North Sea it is known that catch per unit effort in the winter is strongly positively related to both sea surface and sea bottom temperature and also but to a lesser extent, salinity. Thus forecast accuracy in squid production can be improved by taking into account environmental variables (ICES 2003). 17 Conclusion Since G. fabricii may be the most common cephalopod in Greenland waters, it may be presumed that this species would dominate the catch in an experimental squid fishery. The species has a nutritional value, that makes it suitable for consumption and a very high lipid content, which makes it suitable for industrial use (Kristensen 1984). Though less abundant, Rossia moelleri, may also be of commercial interest e.g. in association with the shrimp fishery (Thomas K. Kristensen, pers. com.). Considering the suspected high ecological importance of this resource, any exploitation should be preceded by and subsequently closely accompanied with thorough investigations on stock sizes, distributions and biology in order to assess the fishery potential for a sustainable exploitation of this resource. Acknowledgements We wish to thank: Thomas K. Kristensen (Danish Bilharziasis Laboratory) and Mads Peter Heide-Jørgensen (GINR) for useful comments and information, Uwe Piatkowski and Karsten Zumholz (Institute of Marine Research, Kiel) for providing unpublished data, Marie StorrPaulsen (GINR) for retrieving data from the ground fish surveys conducted by Greenland Institute of Natural Resources, as well as Uwe Piatkowski, Helle Siegstad (GINR) and Bo Bergstrøm (GINR) for comments and ideas that improved the manuscript. 18 References Arkhipkin, A.I. & Bjørke, H. 1999. Ontogenetic changes in morphometric and reproductive indices of the squid Gonatus fabricii (Oegopsida, Gonatidae) in Norwegian Sea. Polar Biology 22, 357-365. Bjørke, H. 2001. Predators of the squid Gonatus fabricii (Lichtenstein) in the Norwegian Sea. Fisheries Research 52, 113-120. Bjørke, H. & Gjøsæter, H. 1998. Who eats the larger Gonatus fabricii (Lichtenstein) in the Norwegian Sea? ICES C.M. 1998/M:10. Collins, M.A. 2002. 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