Long-term changes in the trophic level of western Mediterranean fishery and aquaculture landings

Abstract

We explored changes in western Mediterranean fishery and aquaculture landings using trophic level (TL) estimates derived from nitrogen stable isotope analysis combined with geographically detailed fishery data collated by the General Fisheries Council for the Mediterranean (GFCM). Our analyses confirmed earlier suggestions that there has been a significant decline in the mean trophic level of Mediterranean landings (by ~0.15 TL over 26 years). However, this decline is suggested to be almost entirely a result of increased landings of bivalve molluscs from mariculture and not due to changes in landings from capture fisheries. The mean trophic level of finfish landings has not changed significantly since 1973, although both fish and total landings have become significantly more diverse. Inspection of small pelagic fish landings revealed a marked decrease in the contribution played by anchovy and replacement of this species by sardine. Since 1981, cage culture of high trophic level species such as sea bass (Dicentrarchus labrax) and seabream (Sparus aurata) has become increasingly important, such that when clupeoid landings were excluded from the analyses, the mean trophic level of finfish landings was actually demonstrated to have increased over the past 26 years.