Relation between recruitment, sea surface temperature, and density-independent mortality of the Pacific sardine (Sardinops caeruleus) off the southwest coast of the Baja California Peninsula, Mexico*

The density-independent mortality, considered in the stock-recruitment model of Ricker, was related to the interannual variability of the sea surface temperature (SST) during 1981 to 1993 in Bahia Magdalena, Baja California Sur and Isla Cedros, Baja California, Mexico. From the stock-recruitment curve fitted to the observed data the variation in the density-independent mortality was estimated, maintaining fixed the value of the density-dependent coefficient. The density-independent parameters estimated in this way were related to the SST by using a functional relationship that considers six principal components. This function permitted identification of the changes of the density-independent mortality and its relation to the recruitment of the Pacific sardine Sardinops caeruleus. We determined density-independent mortality greater than 3.38 as years with recruitment greater than 25,000 t, and density-independent mortality less than 3.38 as years with recruitment less than 15,000 t. The seasons of greatest influence on the density-independent mortality in relation to the SST were autumn, winter and spring in both regions (Bahia Magdalena and Isla Cedros). In these seasons when the SST > 19.3°C (warmer waters) the variations in recruitment of Pacific sardine were observed.