An overview of bottom trawl selectivity in the Mediterranean Sea

In the Mediterranean Sea, where bottom trawling for demersal species is the most important fishery in terms of landings, around 75% of the assessed fish stocks are overfished. Its status as one of the world's most heavily exploited seas and the one subject to the highest trawling pressure has become a global concern. An extensive overview of bottom trawl selectivity studies was performed to assess the sustainability of this fishery in the Mediterranean. The selectivity parameters were collected from 93 peer-reviewed publications from 10 countries, totalling 742 records and 65 species. Our review highlighted that i) the catch of the bottom trawls commonly employed in the Mediterranean, although they comply with current codend mesh regulations, still includes immature individuals of 64-68% of the species investigated, and individuals under the minimum conservation reference size (MCRS) of 78% of the species investigated, and that ii) the MCRS set for 59% of the species analysed is well below their length at first maturity and is therefore ecologically inadequate. Although square-mesh codends are slightly more selective, the models developed herein demonstrate that improving size and species selectivity would require considerably larger meshes, which may significantly reduce profitability. The urgent need to mitigate the biological impacts of bottom trawling in the Mediterranean should be addressed by promoting the adoption of more ecologically sustainable fishing gears through the introduction of more selective meshes or of gear modifications.