THE EFFECT OF NATURAL VARIABILITY OF LIFE-HISTORY PARAMETERS ON ANCHOVY AND SARDINE POPULATION-GROWTH

The northern anchovy (Engraulis mordax) and Pacific sardine (Sardinops sagax) populations were modeled with a stage-based matrix to examine how natural variation of life-history parameters affects per capita gr owth. In the model northern anchovy (Engraulis mordax) population, the greatest change in growth results from natural variation in the durat ion of, and the instantaneous mortality rate of, the early and late la rval stages. In the model Pacific sardine (Sardinops sagax) population , the greatest change in growth results from natural variation in the duration of, and the instantaneous mortality rate of, the late larval stage. Temperature determines the duration of both egg and yolk-sac la rval stages and the rate at which prerecruit sardine and anchovy matur e. We believe that changes in the duration of both egg stages and yolk -sac larval stages may have greater effects on population growth than changes in any single stage.