A preliminary life history traits analysis of sharks in the Sea of Marmara (Türkiye), where deoxygenation and habitat deterioration are raising concerns

Abstract

Life history traits of 17 species of sharks occurring in the Sea of Marmara were analysed based on Gower’s distances, Principal Coordinate Analyses, and hierarchical clustering. The analysis shows that the sharks of the Sea of Marmara can ecologically be divided into several clusters. The increasing occurrence of sharks on the Marmara continental shelf, especially in the last few years, suggests that the expected habitat compression due to deoxygenation has begun to take place. This situation, which can be considered as a “habitat trap” for sharks, should be considered as a threat that may lead to shark mortalities due to the intensification of bycatches or even the intentional killing of sharks. Available results are sufficient to predict a disturbing future for sharks of the Sea of Marmara if the factors (deoxygenation, habitat loss, bycatch, etc.) threatening the overall ecosystem do not improve.