Working Group on Fisheries Benthic Impact and Trade-offs (WGFBIT; outputs from 2023 meeting)

The Working Group on Fisheries Benthic Impact and Trade-offs (WGFBIT) develops methods and performs assessments to evaluate benthic impact from fisheries at regional scale, while considering fisheries and seabed impact trade-offs.

In this report, new fishery benthic impact assessments (ToR A) are shown for the Spanish Mediterranean. For other regions, updates of the whole assessment or specific steps only are presented.

In relation to the updates on the assessment framework (ToR B), an alternative indicator to L1 was tested. It is based on the FBIT methodology but only estimates the relative decline in biomass of the 10% most long-lived biomass fraction of the community (PD-sens). The group examined the responsiveness of this indicator to 6 gradients of trawling pressure and compared it with the PD total biomass indicator and two empirically estimated indicators, SoS and long-lived fraction. The results show that the PD-sens is typically as responsive as SoS and long-lived fraction. Furthermore, the overview on the current methodologies used in the FBIT approach across regions is further updated and, in such way, forms the basis for the methodology section of the manuscript in development.

Regarding indicator comparability (ToR C), the work of the Workshop to evaluate proposed assessment methods and how to set thresholds for assessing adverse effects on seabed habitats (WKBENTH 3; ICES, 2022) is transformed into a publication. For certain regions, more indicator comparisons are executed, for example, in the Adriatic Sea.

The WGFBIT ToR D works towards an improved understanding of the link between species functional effect traits and parameters for specific ecosystem functions in order to improve our ability to predict the impact of fishing disturbance on benthic ecosystem functioning. A new assessment examining trawling-induced changes in benthic effect trait composition using multiple case-studies from the North Sea, Celtic Sea, Kattegat, Baltic Sea and the eastern Mediterranean is presented. Work continues to quantify relationships between species traits and biogeochemical parameters and to develop a data-driven mechanistic model to predict changes in the trajectories of species densities, bioturbation and bioirrigation potential over time due to trawling.