Interactions between demersal fish body condition and density during the regime shift of the Gulf of Lions

Abstract

Abstract Environmentally driven changes in small pelagic fish condition and size have been observed in the Gulf of Lions (GOL) since 2008, leading to a significant fishery crisis. However, the effect of changes in environment and/or in the small pelagic community on the demersal community remain unknown. For the first time, this study examines the body condition (bc) and population density of 22 demersal species since 1994, using dynamic factor analysis (DFA). Most (but not all) of demersal species have shown a common shift between 2006 and 2009, which is synchronous with that observed in small pelagic species and the environmental conditions in the GOL. It had been concluded that the environmentally driven changes detected in the pelagic fish community also affected the demersal fish community, but with less drastic and lasting consequences. As the DFA revealed that the bc displayed important variations for several species, notably hake (Merlucius merluccius), the interaction between the bc and population density was investigated using the Multivariate Autoregressive (MAR) model on hake population at three life stages (recruits, juveniles, and adults). Results showed that adult bc, while negatively affected by density, had a positive effect on recruitment. So hake bc could have affected population dynamics by promoting higher recruitment at low densities. Further work is needed to ascertain whether such effects exist in other demersal species.