Environmental control of the recruitment of sardines (Sardina pilchardus) over the western Saharan shelf between 1995 and 2002 : a coupled physical/biogeochemical modelling experiment

International audience; Fisheries constitute an important economic sector for Morocco, where the species Sardina pilchardus represents the main landings. In acoustic evaluations conducted along the Moroccan coast since 1995, the absence of juveniles in 1996 and 1998 and the collapse of the sardine stock between 1996 and 1997 represent the main events until 2002. Sardines are known to be microphageous planktivores and thus are sensitive to environmental variability. A biogeochemical model coupled to a hydrodynamic model (ROMS) was run over the Canary Current System (1991-2002) to investigate the environmental factors that could have played a role in the variability of the sardine spawning. A grid refinement (1/12 degrees) centred on the Saharan Bank (SB) region was built to study the main spawning ground of sardines off northwest Africa. The volume of the potential spawning habitat (PSH) of sardines was defined as a function of depth, temperature and salinity, which are included in the ranges 0-200 m, 15-21 degrees C and 35.8-36.8, respectively. Our modelling frame was able to reproduce the seasonal cycle of temperature, phytoplankton concentration and PSH over the SB. It also captured the warming associated with the negative index of the North Atlantic Oscillation of 1995-1997 and allowed a description of the inter-annual variability of the PSH. Our experiment shows that the volume of PSH was much reduced in 1996 compared to the other years. The results suggest that the delay between high abundance of plankton and favourable spawning conditions is a good proxy for determining the recruitment failure of sardine in this oceanic region.