Fishing drives loss of shark and ray in the Adriatic

The small-spotted catshark, Scyliorhinus canicula, is one of the species that underwent the largest decline in the Adriatic Sea.© Giacomo Chato Osio, 2013 The small-spotted catshark, Scyliorhinus canicula, is one of the species that underwent the largest decline in the Adriatic Sea.© Giacomo Chato Osio, 2013

Shark and ray communities in the Adriatic Sea have been highly depleted in recent years, with fishing being a key driver of the decline.

This is the result of a study co-authored by the Joint Research Centre (JRC) and published in Nature Scientific Reports.

The study combined and standardised catch data from five trawl surveys conducted between 1948 and 2005 to evaluate long-term trends in the Adriatic Sea elasmobranch (a subclasses of cartilaginous fish) populations, which counted 33 different species (12 shark species, 20 rays and one chimaera). Since 1948, catch rates of these populations have declined by 94% and 11 species have ceased to be detected. Shark and rays are important components of the marine ecosystem and their loss can severely impact food web dynamics.

The abundance of these species can decline considerably with fishing, but assessing the drivers of community changes can be complicated due to interactions between species and variations in vulnerability and exposure to fishing. An observational approach across gradients of natural or human-induced changes is an efficient alternative. The Adriatic Sea offered an ideal case study due to its long history of human-induced changes and the differences between the eastern Italian coast, exposed to extremely high exploitation pressure and the Croatian coast, which sustained a much lighter fishing exploitation.

The article reports a greater abundance and diversity of elasmobranchs in the eastern Adriatic, reflecting the less intense historical and recent fishing pressure in Croatian compared to Italian waters. Results show that the exploitation history and changes in fishing pressures could explain most of the observed patterns of abundance and diversity, including the absence of strong compensatory increases.

The study highlights the importance of examining historical data for understanding long-term dynamics of marine species and supporting current decisions. It also suggests that careful planning and international management of developing fisheries in the Adriatic and the creation of ecological corridors and large-scale protected areas could help to promote recovery of shark and ray communities. The findings are also of major relevance to recent EU policy and legislation initiatives on the conservation and management of sharks.

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