Shark Diversity, Bycatch, and Conservation Importance in the Northeastern Mediterranean Sea

Sharks are among the most threatened marine vertebrates in the Mediterranean Sea, where sustained fishing pressure has raised increasing conservation concerns. This study assessed shark bycatch composition, occurrence, spatial distribution, and conservation status in commercial bottom-trawl operations conducted in İskenderun, Mersin, and Antalya Bays in the northeastern Mediterranean Sea during 2019–2020. Of 91 commercial trawl operations examined, 21 yielded shark bycatch, comprising 147 individuals from 12 species with a combined wet weight of 404.76 kg. Mustelus mustelus was the most numerically abundant species, accounting for 52 individuals recorded across eight shark-positive hauls. Other species of conservation concern, including the Critically Endangered Squatina oculata, S. aculeata, and Centrophorus granulosus, were also recorded. Species composition and species-specific catch per unit effort (CPUE) varied among sampled locations and associated depth and bottom-habitat conditions. However, CPUE values were calculated from shark-positive hauls and therefore represent observed catch rates rather than estimates of population abundance or standardized catch rates across all commercial operations. Furthermore, the unbalanced sampling design and confounding among region, season, depth, and habitat precluded assessment of their independent effects on shark occurrence. The recorded assemblage included species classified as Critically Endangered, Endangered, or Vulnerable on the IUCN Red List, highlighting the conservation relevance of incidental shark captures in active commercial bottom-trawl fisheries. These findings provide a descriptive baseline for future standardized monitoring and support continued efforts to improve species-level monitoring and evaluate bycatch mitigation measures in northeastern Mediterranean demersal fisheries.