The influence of mesoscale ocean processes on anchovy (Engraulis encrasicolus) recruitment in the Bay of Biscay estimated with a three-dimensional hydrodynamic mode

The relationship between anchovy (Engraulis encrasicolus) recruitment in th e Bay of Biscay and environmental variables during their planktonic phase ( March to July) was investigated from 1986 to 1997. Meteorological variables (wind and temperature) are forcing effects on the sea, but they are not th ought to be processes that govern larval survival directly. Food-web dynami cs are believed to be more closely linked to larval survival and are relate d to the physical vertical water column structure. Therefore, we used a thr ee-dimensional (3D) hydrodynamic model to characterize three major physical mesoscale processes affecting vertical structure in south-cast Biscay: str atification, upwelling and river plume extent. Indices were estimated from the model outputs to characterize and quantify the space/ time evolution of these structures during the period March to July. A multiple linear regres sion analysis was then used to analyse hierarchy in the explanatory power o f the physical indices. Coastal upwelling and shelf stratification breakdow n indices were the most significant explanatory variables, with positive an d negative effect on recruitment, respectively. A model with these two indi ces explains 75% of the recruitment variability of anchovy observed in the period 1987-96.