First record of the white trevally (Pseudocaranx dentex) in the Black Sea: a new occurrence from Bulgarian coastal waters

139 First record of the white trevally (Pseudocaranx dentex) in the Black Sea: a new occurrence from Bulgarian coastal waters Radoslava Bekova1, Bogdan Prodanov2 1 Department of Marine Biology and Ecology, Institute of Oceanology – Bulgarian Academy of Sciences, Varna, Bulgaria 2 Coastal Zone Dynamics Department, Institute of Oceanology – Bulgarian Academy of Sciences, Varna, Bulgaria Corresponding author: Radoslava Bekova (radoslav[email protected]) Copyright: © Radoslava Bekova & Bogdan Prodanov. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0). Short Communication Abstract This study documents the first confirmed record of the white trevally (Pseudocaranx dentex) in the Black Sea. A specimen (354 mm TL and weight 703 g) was recorded near Varna, Bulgaria, on 24 July 2025. This observation represents the northernmost occurrence of the species along the western Black Sea coast, extending its known distribution beyond the transitional zone of the Bosphorus. The present record from Varna Bay is located approximately 330 km north of the previous northernmost confirmed occurrence in the Bosphorus Strait, marking a substantial northward extension along the western Black Sea coastline. Identification was based on morphological and meristic characteristics. Despite abundant benthic prey in the area, the specimen’s empty stomach may indicate a recent arrival or a trophic mismatch. The finding supports the hypothesis of meridionalization and climate-driven range shifts of thermophilic fishes. Sea surface temperatures in the region have increased by ~0.5 °C per decade since the 1990s, creating favorable conditions for warm-water species. As a fast-growing, generalist predator, P. dentex may alter food web dynamics and interact with native species. This record underscores the need for sustained ichthyofaunal monitoring and further research on the ecological implications of thermophilic newcomers in the Black Sea. Key words: Climate-driven dispersal, marine biodiversity monitoring, meridionalization, range expansion, thermophilic species, western Black Sea Introduction The white trevally, Pseudocaranx dentex (Bloch & Schneider, 1801), is a thermophilic carangid fish that inhabits marine and brackish waters in tropical and subtropical regions across all major ocean basins. However, it is also occasionally found in temperate zones (Froese and Pauly 2023). The species is reef-associated and typically occurs at depths of 10–25 m, although it has been recorded down to 238 m. The species exhibits a broad Indo-Pacific distribution, including the coasts of South Africa, Japan, Australia, New Zealand, Hawaii, Lord Howe and Norfolk Islands, and New Caledonia. It is also present in the western Atlantic from North Carolina and Bermuda to southern Brazil and in the Academic editor: Kremena Stefanova Received: 13 August 2025 Accepted: 26 October 2025 Published: 21 November 2025 ZooBank: https://zoobank. org/35FF61AF-5F37-487C-82F2F8A9224AF6C6 Citation: Bekova R, Prodanov B (2025) First record of the white trevally (Pseudocaranx dentex) in the Black Sea: a new occurrence from Bulgarian coastal waters. Nature Conservation 60: 139–149. https://doi.org/10.3897/ natureconservation.60.168638 Nature Conservation 60: 139–149 (2025) DOI: 10.3897/natureconservation.60.168638 This article is part of: Black Sea ecosystem in the spotlight Edited by Kremena Stefanova, Snejana Moncheva, Ertuğ Düzgüneş, Lyubomir Dimitrov 140 Nature Conservation 60: 139–149 (2025), DOI: 10.3897/natureconservation.60.168638 Radoslava Bekova & Bogdan Prodanov: White Trevally (Pseudocaranx dentex) in the Bulgarian Black Sea eastern Atlantic and adjacent seas, ranging from the Mediterranean and the Azores to Madeira, the Canary Islands, Cape Verde, Ascension Island, and St. Helena (Froese and Pauly 2023). P. dentex is characterized by a fusiform, laterally compressed body, metallic greenish-blue dorsally and silvery white ventrally, with a prominent dark blotch on the operculum and a yellow stripe along the midline. Meristic features include 9 dorsal spines, 25–26 dorsal soft rays, 3 anal spines, 21–22 anal soft rays, and 25 vertebrae (Smith-Vaniz 1986; Kailola et al. 1993). The lateral line bears 57–78 scales on its curved section and 34–46 scutes posteriorly (Neira et al. 1998). Adults typically inhabit coastal waters, bays, and estuaries, forming schools near the bottom or around reefs and rough substrates, whereas juveniles are more common in shallower estuarine and shelf habitats (May and Maxwell 1986; Kailola et al. 1993). Feeding strategies include ram-filtering and suction feeding on plankton and benthic invertebrates (Annala 1994; Sazima 1998). Reproduction involves pelagic eggs (Smith-Vaniz 1986). The presence of P. dentex has been well documented in the Mediterranean Sea. In the western basin, it was reported along the eastern and southern Adriatic coasts by Pallaoro and Jardas (1996) and Dulčić et al. (2003), and along the Italian coast by Costa (1991). More recently, Tiralongo et al. (2018) recorded the species on the southeastern coast of Sicily between 2013 and 2017. Azzurro et al. (2013) noted its regular presence in fish assemblages around Lampedusa Island in the Strait of Sicily. In the eastern Mediterranean, the species has been reported in Syrian waters (Saad 2005), in the Levantine Sea (Gücü and Bingel 1994), and off the coast of North Cyprus during 2015–2016 (Yalgın and Türker 2023). It has also been observed along the Libyan coastline in the southern Mediterranean (Elbaraasi et al. 2019). In the Aegean Sea, Giakoumi and Kokkoris (2013) documented the species in the coastal waters of the Cyclades Archipelago during 2007–2008. More extensive monitoring by Tüney-Kızılkaya et al. (2020) confirmed the presence of P. dentex around fish aggregation devices (FADs) in Kuşadası Bay, aquaculture cage areas in Güllük Bay, and reef habitats in Gökova Bay between 2009 and 2019. This observation constitutes the first confirmed record of P. dentex in Bulgarian Black Sea waters and represents a significant northward extension of the species’ known distribution into the Black Sea proper. Earlier investigations on ichthyofauna and fish trap catches from the Bosphorus region already indicated the presence of thermophilic Mediterranean elements in the transitional waters between the Marmara and the Black Sea (Aydınyazıcı and Öker 1960). The previous northernmost record was reported from the Beykoz coast in the Bosphorus Strait (Keskin 2023), in the transitional zone of the Mediterranean–Black Sea interface. The aim of this report is to document and describe the first confirmed occurrence of P. dentex in the fully marine coastal waters of the Black Sea, based on a specimen captured near Varna, Bulgaria. Morphological and meristic traits are analyzed to confirm the species identification, and potential climatic and ecological drivers of this occurrence are discussed in the context of recent warming trends and range expansions of thermophilic fishes in the region. 141 Nature Conservation 60: 139–149 (2025), DOI: 10.3897/natureconservation.60.168638 Radoslava Bekova & Bogdan Prodanov: White Trevally (Pseudocaranx dentex) in the Bulgarian Black Sea Materials and methods On 24 July 2025, a recreational diver used a speargun to capture a specimen of P. dentex in shallow coastal waters (depth ~4.5 m) near Trakata, Varna, Bulgaria (43°13.04061'N, 27°58.63438'E) (Fig. 1A–B). The fish was photographed in situ and preserved on ice before being measured and weighed. Sixteen morphometric characteristics were measured following Smith-Vaniz (1986) and are listed in Table 1 and illustrated in Fig. 3: (1) total length, (2) body depth, (3) head length, (4) snout length, (5) orbit diameter, (6) upper jaw length, (7) lower jaw length, (8) distance from snout tip to first dorsal fin Figure 1. A. Location of the first confirmed record of Pseudocaranx dentex in the Black Sea; B. Location of the record in the Bulgarian Black Sea coastal waters at the Trakata locality, Varna Bay (red point). 142 Nature Conservation 60: 139–149 (2025), DOI: 10.3897/natureconservation.60.168638 Radoslava Bekova & Bogdan Prodanov: White Trevally (Pseudocaranx dentex) in the Bulgarian Black Sea origin, (9) to second dorsal fin origin, (10) to pectoral fin insertion, (11) to pelvic fin insertion, (12) to anal fin origin, (13) pelvic fin length, (14) pectoral fin length, (15) interorbital length, and (16) standard length. All measurements were taken with a digital caliper to the nearest 0.1 mm and expressed in centimeters. No meristic features were recorded. Results Based on body morphology and coloration, the specimen was identified as Pseudocaranx dentex—a deep-bodied, laterally compressed fish with a metallic bluish-green dorsal surface, silvery flanks, and a characteristic dark spot on the operculum. The specimen measured 354 mm in total length, 285 mm in standard length, and weighed 703 g. The species determination was confirmed using keys provided in regional ichthyological literature and was consistent with the description in Keskin (2023). The present record from Varna Bay at coordinates 43°13.04061'N, 27°58.63438'E, at a depth of ~4.5 m on a sandy bottom, is located ~330 km north of the previous northernmost confirmed occurrence of P. dentex in the Bosphorus Strait (Keskin 2023), representing a substantial northward extension along the western Black Sea coastline (Fig. 1). After removing the stomach, it was found to be empty. Table 1. List of morphometric characteristics measured from the specimen of Pseudocaranx dentex from Varna Bay, Bulgaria, on 24 July 2025. №Morphometric characteristic Abbrev. Definition (from…to…) Length (cm) % TL* % HL* 1 Total length TL Snout tip to caudal fin tip 35.4 100.0 343.7 2Body depth at the first dorsal fin origin BD Maximum body depth at D1 origin 10.7 30.2 103.9 3 Head length HL Snout tip to posterior margin of operculum 10.3 29.1 100.0 4Snout to second dorsal fin origin S–D2 Snout tip to D2 origin 16.6 46.9 161.2 5 Diameter of orbit ED Horizontal eye diameter 1.8 5.1 17.5 6 Upper jaw length UJL Anterior tip of premaxilla to posterior end of maxilla 3.4 9.6 33.0 7 Lower jaw length LJL Anterior tip of dentary to posterior end of mandible 7.7 21.8 74.8 8Snout to first dorsal fin origin S–D1 Snout tip to D1 origin 11.8 33.3 114.6 9 Snout length SnL Snout tip to anterior margin of orbit 3.9 11.0 37.9 10 Snout to pectoral fin insertion S–P Snout tip to pectoral fin insertion 10.2 28.8 99.0 11 Snout to pelvic fin insertion S–V Snout tip to pelvic fin insertion 10.6 29.9 102.9 12 Snout to anal fin origin S–A Snout tip to anal fin origin 19.1 54.0 185.4 13 Pelvic fin length VFL Pelvic fin base to tip 5.4 15.3 52.4 14 Pectoral fin length PFL Pectoral fin base to tip 11.0 31.1 106.8 15 Interorbital length IO Shortest distance between the orbits (dorsal view) 9.7 27.4 94.2 16 Standard length SL Snout tip to caudal peduncle (end of hypural plate) 28.5 80.5 276.7 *TL – total length; HL – head length. Percentages are calculated relative to TL or HL, depending on anatomical context. 143 Nature Conservation 60: 139–149 (2025), DOI: 10.3897/natureconservation.60.168638 Radoslava Bekova & Bogdan Prodanov: White Trevally (Pseudocaranx dentex) in the Bulgarian Black Sea Figure 3. Diagram of morphometric characteristic measurements taken from the specimen of Pseudocaranx dentex from Varna Bay, Bulgaria, in 2025 (numbers correspond to morphometric characteristics listed in Table 1). Figure 2. Pseudocaranx dentex and species from the family Mugilidae (Mugil cephalus, Chelon auratus) from the Trakata locality, Varna Bay, Bulgarian Black Sea coastal waters. 144 Nature Conservation 60: 139–149 (2025), DOI: 10.3897/natureconservation.60.168638 Radoslava Bekova & Bogdan Prodanov: White Trevally (Pseudocaranx dentex) in the Bulgarian Black Sea The diagnostic features of the examined specimen include an elongate, deep, and moderately compressed body, an elongated snout, and a weakly developed adipose eyelid. The upper jaw terminates anterior to the eye margin. The cleithrum margin is smooth and lacks papillae. Both jaws bear a single row of blunt, conical teeth, and additional teeth are present on the tongue. The spinous portion of the dorsal fin is relatively high, with the longest spine exceeding the height of the soft dorsal lobe. The pectoral fins are longer than the head, and the entire body is covered with small cycloid scales. The body coloration is pale greenish-blue dorsally and silvery ventrally, with a prominent black spot on the posterodorsal margin of the operculum and a yellow lateral stripe that broadens posteriorly. The bases of the soft dorsal and anal fins exhibit yellow pigmentation, whereas the caudal and soft dorsal fins are dusky yellow (Fig. 2). All morphometric and meristic characteristics correspond well with the descriptions provided by Smith-Vaniz (1986). A key distinguishing trait of P. dentex is the notably long first dorsal spine, which exceeds the height of the second dorsal fin lobe. In addition to the morphometric measurements, the following meristic features were recorded for the examined specimen: 9 dorsal spines, 24 dorsal soft rays, 3 anal spines, 20 anal soft rays, and 25 vertebrae. The lateral line was composed of 57 scales in the curved portion and 39 posterior scutes. These values fall within the range reported for P. dentex in Mediterranean and Atlantic populations (Smith-Vaniz 1986; Neira et al. 1998), further supporting the taxonomic identification of the specimen. Discussion The white trevally is a thermophilic marine fish belonging to the family Carangidae. It is considered medium-sized, with a typical standard length of around 400 mm (Smith-Vaniz 1986). The maximum reported size in the Mediterranean is 702 mm TL and 4,126 g (Tüney-Kızılkaya et al. 2020). However, information on the Mediterranean population of P. dentex remains limited, particularly regarding its distribution, feeding ecology, and reproductive biology (Dulčić et al. 2003). According to existing knowledge, P. dentex typically inhabits inshore waters, with juvenile individuals forming shoals and feeding primarily on fish larvae and post-larvae (Dulčić et al. 2003), as well as euphausiid larvae, amphipods, copepods, and gastropods (Russell 1983). Adult individuals are more solitary and feed on a broad spectrum of benthic invertebrates, including squid, cuttlefish, finfish, crabs, shrimps, sea stars, sea urchins, and bivalves (Froese and Pauly 2023). Spawning generally occurs during the summer months (Smith-Vaniz 1986). Juveniles are frequently observed trailing behind species such as mullets and striped seabream in sandy-bottom habitats, often utilizing floating structures for shelter from predators. Both net and hook fisheries target the species, and in the southern Mediterranean, it is also caught using fish aggregating devices (FADs) (Deudero et al. 1999). Marine biodiversity, including fish species such as P. dentex, is increasingly threatened by multiple anthropogenic pressures, including climate change, pollution, habitat degradation, overexploitation of resources, and eutrophication. Among these, global warming has emerged as a key driver of distributional shifts. Thermophilic and temperate fish species with broad 145 Nature Conservation 60: 139–149 (2025), DOI: 10.3897/natureconservation.60.168638 Radoslava Bekova & Bogdan Prodanov: White Trevally (Pseudocaranx dentex) in the Bulgarian Black Sea thermal tolerance (~10 °C) are exceptionally responsive to temperature changes, enabling them to maintain positive growth rates under varying thermal conditions (Pauly 2010; Cheung et al. 2013). The term “meridionalization” has been used to describe the northward range expansion of such species in both the Mediterranean and adjacent regions (Bianchi and Morri 1993). This latitudinal shift, driven by ocean warming, is recognized as one of the most observable biotic responses to climate change, particularly in marine ecosystems (Francour et al. 1994; Azzurro 2008). For instance, P. dentex and other thermophilic species such as Epinephelus marginatus and Caranx crysos have been documented to expand their distribution northwards in the Mediterranean Sea (Azzurro 2008). In this context, Keskin (2023) reported the northernmost known occurrence of P. dentex within the Mediterranean–Black Sea transition zone, based on two individuals captured near the Beykoz coast in the Bosphorus Strait (Fig. 1A). However, due to the transitional nature of the Bosphorus, which retains characteristics more typical of the Marmara Sea in terms of oceanography and fauna, that record may not represent actual penetration into the Black Sea basin. By contrast, the present finding from Varna Bay constitutes the first confirmed occurrence of P. dentex in offshore waters of the western Black Sea, marking the species’ first verified presence in the Black Sea proper and extending its known distribution range (Fig. 1A–B). The examined specimen had an empty stomach, a finding of particular interest given the species’ typical diet of benthic invertebrates and small demersal fishes. Along the Bulgarian Black Sea coast, potential prey organisms such as crustaceans (Crangon crangon, Palaemon elegans), mollusks (Mytilus galloprovincialis, Donax trunculus), and polychaetes (Hediste diversicolor) are commonly found in coastal benthic habitats. The absence of food in the stomach may indicate either recent arrival and incomplete acclimatization to local feeding grounds or a broader mismatch between preferred prey and the current state of the benthic community—a scenario potentially linked to ongoing ecological shifts in the Black Sea. This observation extends the known distribution of P. dentex by ~330 km northwards from the Bosphorus Strait (Keskin 2023) into the open coastal waters of the western Black Sea. Such a distance is notable for a single confirmed record and supports the view that the species is capable of substantial range shifts in response to changing environmental conditions. Climate change and thermophilic species Recent analyses confirm a persistent rise in sea surface temperature (SST) and increased marine heatwave (MHW) frequency in the Black Sea (Bat et al. 2024). These patterns are consistent with climate-induced range expansions observed for thermophilic species. Notably, the presence of P. dentex in fully marine offshore waters of the western Black Sea coincides with a well-documented long-term warming trend in the region. Satellite-based SST observations for the Black Sea show a statistically significant increase of approximately 0.65 ± 0.07 °C per decade from 1982 to 2020 (Mohamed et al. 2022), with persistent warming across seasons. This rise is accompanied by increased frequency and duration of MHWs, with observed trends of 1.4 additional events and 2.8 extra 146 Nature Conservation 60: 139–149 (2025), DOI: 10.3897/natureconservation.60.168638 Radoslava Bekova & Bogdan Prodanov: White Trevally (Pseudocaranx dentex) in the Bulgarian Black Sea MHW days per decade. Such changes can enhance habitat suitability for thermophilic species and promote their establishment in previously cooler regions. These findings are supported by operational data from the Copernicus Marine Service (CMS 2024), which estimate a cumulative SST trend of approximately 0.5 °C per decade along the western Black Sea coast since the early 1990s. Together, these lines of evidence indicate that thermal conditions in the region are becoming increasingly favorable for subtropical and temperate-affinity species such as P. dentex. The new record, therefore, provides further evidence that climate-driven thermal changes are actively reshaping species distributions in the Black Sea. The likely climate-related arrival of P. dentex aligns with the observed meridionalization processes across the Mediterranean–Pontic region. This new record reinforces concerns that climate-induced shifts in species distributions are already affecting the ichthyofaunal composition of the Black Sea. The arrival of thermophilic species such as P. dentex may lead to competition with native taxa, changes in trophic interactions, and broader alterations in ecosystem functioning. The northward expansion of thermophilic species such as P. dentex may have cascading ecological implications, including competition with native species and alteration of food web dynamics. This highlights the importance of sustained monitoring and adaptive management strategies under changing climatic conditions. Conclusion This report documents the first confirmed occurrence of P. dentex in the coastal waters of the Black Sea, located in Varna Bay, Bulgaria, representing a notable extension of the species’ known range within the northeastern Mediterranean– Black Sea system. Compared to previous records limited to the transitional zone of the Bosphorus (Keskin 2023), the finding near Varna marks the northernmost confirmed occurrence in fully marine offshore conditions of the western Black Sea. This observation aligns with a broader regional warming trend and supports the hypothesis of ongoing meridionalization and climate-driven range expansion of thermophilic marine fishes. The specimen’s morphometric and meristic characteristics were consistent with known species descriptions, confirming its identity. The empty stomach is notable given the abundance of suitable benthic prey along the Bulgarian coast. It suggests a recent arrival or a possible trophic mismatch, potentially reflecting broader ecological changes within local benthic communities. Long-term SST analyses for the Black Sea indicate a statistically significant warming of approximately 0.6–0.65 °C per decade since the early 1980s (Mohamed et al. 2022), with additional confirmation from Copernicus Marine Service indicators estimating ~0.5 °C per decade in western coastal areas (CMS 2024). This warming is also associated with increasing frequency and duration of marine heatwaves, which affect species migration, establishment, and trophic stability. Therefore, the presence of P. dentex may reflect these climate-mediated habitat shifts. Given accelerating SST trends, this record provides further evidence of climate-induced biogeographic shifts in the Black Sea. It highlights the need 147 Nature Conservation 60: 139–149 (2025), DOI: 10.3897/natureconservation.60.168638 Radoslava Bekova & Bogdan Prodanov: White Trevally (Pseudocaranx dentex) in the Bulgarian Black Sea for systematic ichthyofaunal monitoring to detect emerging distributional patterns, assess ecological impacts on native communities, and inform adaptive conservation and fisheries management in the face of rapidly changing marine conditions. The entry of P. dentex into the Black Sea is ecologically significant because it represents the arrival of a mobile, opportunistic predator capable of exploiting diverse prey resources and occupying midto upper trophic levels. As a fast-growing and generalist species, P. dentex may influence native food webs through predation, competition, or indirect ecological interactions. Its successful establishment under warming conditions could signal broader functional changes within the Black Sea ecosystem, especially if other thermophilic species follow similar trajectories (Russell 1983; Azzurro 2008; Cheung et al. 2013; Froese and Pauly 2023). Acknowledgements The authors express their gratitude to Nikolay Stefanov for capturing the specimen and to Dragomir Enev for facilitating the connection. Additional information Conflict of interest The authors have declared that no competing interests exist. Ethical statement No ethical statement was reported. Use of AI No use of AI was reported. Funding The publication was financially supported by the project “Raising public awareness, mapping and reducing anthropogenic waste for the protection of the Bulgarian Black Sea beaches and dunes,” Grant № А24-677, part of the scientific research program of the DER TOURISTIK FOUNDATION, Germany. Author contributions Radoslava Bekova conceived and designed the study, conducted the literature review, identified species, performed morphological and meristic analyses, and prepared the initial manuscript draft. Bogdan Prodanov processed the GIS data, refined the figures, and carried out a critical review and revision of the manuscript. Both authors approved the final version for publication. Author ORCIDs Radoslava Bekova https://orcid.org/0000-0002-9353-1956 Bogdan Prodanov https://orcid.org/0000-0002-8118-3034 Data availability All of the data that support the findings of this study are available in the main text.