Yet another giant for protection: Distribution and status of the bluntnose sixgill shark, Hexanchus griseus (Hexanchiformes: Hexanchidae), in Turkish seas

06/09/2023 Arda Tonay

Yet another giant for protection: Distribution and status of the bluntnose sixgill shark, Hexanchus griseus (Hexanchiformes: Hexanchidae), in Turkish seas

Hakan Kabasakal 

ORCID ID: 0000-0001-8189-9748 

Institute of Science, Fisheries Technologies and Management Program, Istanbul University, 34116 Fatih, İstanbul, TÜRKİYE
Ichthyological Research Society, İstanbul, TÜRKİYE

Abstract

Bluntnose sixgill shark, Hexanchus griseus (Bonnaterre, 1788), occurrs in Turkish waters from the eastern Black Sea to the eastern Mediterranean. Impacts of environmental deteriorations on bluntnose sixgill shark’s distribution in the Black Sea (GSA 29), where the deep zone of the sea is permanently anoxic due to hydrogene sulphide contamination, and in the Sea of Marmara (GSA 28), where the hypoxia has been a raising concern for the last 40 years, is another issue in question. A decreasing trend in mean lengths of bluntnose sixgill sharks over the entire period (1967-2022) was found, which supposed “growth overfishing” of H. griseus in Turkish waters. Available information suggests possible breeding grounds of H. griseus in the Sea of Marmara, in the northern Aegean Sea (GSA 22) and in the northeastern Mediterranean Sea (GSA 24). The overlap of major fishing grounds of Turkish commercial bottom-trawling fleet with those suggested breeding grounds in the northern Aegean Sea and in the northeastern Mediterranean Sea, may cause further threat on the survival of the new generations of H. griseus in Turkish waters. Therefore, it is clearly seen that a management and conservation plan of H. griseus in Turkish waters should not solely rely on banning to capture and retain of bluntnose sixgill sharks on board, but should also provide a methodology to the fishermen of how to keep them alive to decrease or even prevent the at-vessel or post-release mortality. Such a plan should also implement an integrated ecosystem management approach for the conservation of those proposed breeding grounds.

Keywords: Hexanchidae, population, trend, conservation, overfishing, bycatch

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