Seabed sensitivity to bottom trawling in the French Mediterranean. Application of ICES WGFBIT assessment framework

The Mediterranean continental shelf’s benthic habitats have been subjected to high-intensity bottom trawling for decades. This has resulted in benthic biodiversity erosion and degraded seabed conditions. The ICES Working Group on Fisheries Benthic Impact and Trade-offs (WGFBIT) has developed an assessment framework, based on the life history trait longevity, to evaluate the benthic impact from fisheries at regional scale. In this study, the framework is applied to the French Mediterranean. First, we collated Mediterranean longevity databases and developed a common database based on fuzzy coding of longevity classes to be applied to the French data (by-catch benthic invertebrates data resulting from scientific bottom trawl monitoring surveys). This database was then used to associate existing benthic biomass data with longevity classes. Then, a multinomial GLMM was fitted, linking biomass per longevity class to environmental predictors. Next, we used this model to predict the average benthic community longevity value under reference conditions as a proxy of benthic sensitivity. We predicted more sensitive habitats in upper/lower bathyal sediment, and less sensitive habitats in the more shallow, muddy sediments. Last, the predicted longevity curve parameters were used to estimate local carrying capacity and benthic vulnerability (expressed as Relative Benthic State) based on known fixed depletion rates, the observed biomass and abrasion rate. In agreement with previous studies, our Relative Benthic State estimate suggested highly impacted area’s close to the coast in the Gulf of Lion, and lowest impacted habitats around Corsica. Many uncertainties remain and this first preliminary application will need to be further developed and validated in the future