Researchers identify key factors for the survival of sharks caught accidentally in the Mediterranean

A team from the Cavanilles Institute of Biodiversity and Evolutionary Biology (ICBiBE) at the University of Valencia has identified the main factors explaining the mortality of sharks accidentally caught in trawl fisheries in the western Mediterranean. Conducted in collaboration with the Catsharks Association for the study and conservation of elasmobranchs and their ecosystems, the study analysed 2,445 specimens of two very common small shark species in the Mediterranean: the small-spotted catshark (Scyliorhinus canicula) and the blackmouth catshark (Galeus melastomus).

The results show that mortality increases sharply when air temperatures exceed 20°C in the case of the small-spotted catshark – a shallow-water species – and 16°C in the case of the blackmouth catshark, a deep-water species. The risk also rises when specimens remain on deck for more than 15 minutes, long enough for exhaustion and lack of oxygen to compromise their recovery. Body size is another factor, as the article notes that smaller specimens are more vulnerable to the physiological stress caused during capture.

“Investing in practices that make fishing compatible with conservation means investing in more resilient seas and in a sustainable future both for biodiversity and for those who depend on the sea”, explains David Ruiz-García, researcher at ICBiBE and lead author of the study.

“Knowing these thresholds allows us to propose specific measures to improve the survival of sharks caught accidentally”, adds David March (ICBiBE), co-author of the study.

The team proposes a combination of preventive measures, such as protecting key areas for juveniles through spatial and temporal closures adapted to periods of highest risk, modifying fishing gear to increase selectivity, and introducing improvements in on-board handling, for instance, releasing specimens quickly or reducing their exposure to high temperatures.

“Working together with the fishing sector is essential for these measures to be effectively integrated and bring benefits for both shark conservation and fishing activity”, notes Claudio Barría, from the Department of Functional Biology at the University of Oviedo, co-author of the work.

The research, recently published in Conservation Biology, is part of the ECEME project with support from the Biodiversity Foundation of the Spanish Ministry for Ecological Transition and Demographic Challenge (MITECO).

Reference:
Ruiz-García D., Barría C., Raga J.A., March D. (2025). Key drivers of at-vessel mortality in demersal sharks. Conservation Biology. https://doi.org/10.1111/cobi.70100