Fishing for function: the use of biological traits to evaluate the effects of multispecies fisheries on the functioning of fisheries assemblages

The Ecosystem Approach to Fisheries Management claims that fisheries management should take into account the ecosystem processes; in that context, it is useful to examine the functional traits of fisheries assemblages. This can be a challenge in multispecies fisheries. We used 21 biological traits of 86 species to investigate the relationship between-species and trait composition and to identify species with rare functional traits. Combining these traits with two catch datasets from the eastern Mediterranean (Patraikos Gulf: small-scale fleet, eastern Ionian Sea: entire multispecies fleet), we investigated whether certain fishing tactics or gears tend to remove specific traits, using multivariate methodologies. Species and traits composition of the catches were related, but an important part of trait variability was not explained by species composition. Rare traits and trait combinations were found for important target or bycatch species. Differences in the traits composition of fishing operations were revealed both between fishing tactics (Patraikos) as well as gears and areas (eastern Ionian); hierarchical clustering and MDS indicated the distinction of purse-seine catches at gear level. SIMPER analysis by trait indicated associations of certain trait categories mainly with purse-seines (at gear level) and longline métiers and a trammel-net métier (at métier level). The identification of rare traits or their combinations can have significant management implications as overfishing of the species with these traits could result in altering assemblage functioning. It seems that the multispecies character of the benthic fisheries results in a balanced trait removal, while management should regulate the effects of purse-seine fisheries on the fisheries assemblage functioning. Further investigation of the functions that fishing may remove from the ecosystem could contribute to understanding the effects of fishing and reveal overlooked aspects useful for the improvement of fisheries management.