INDIVIDUAL-BASED MODEL OF YOUNG-OF-THE-YEAR STRIPED BASS POPULATION-DYNAMICS .2. FACTORS AFFECTING RECRUITMENT IN THE POTOMAC RIVER, MARYLAND

An individual-based model of the population dynamics of young-of-the-y ear striped bass Morone saxatilis in the Potomac River, Maryland, was used to test the hypothesis that historically high recruitment variabi lity can be explained by changes in environmental and biological facto rs that result in relatively small changes in growth and mortality rat es of striped bass larvae. The four factors examined were (1) size dis tribution of female parents, (2) zooplankton prey density during the d evelopment of striped bass larvae, (3) density of competing larval whi te perch M. americana, and (4) temperature during larval development. Simulation results suggest that variations in female size and in prey for larvae alone could cause 10-fold variability in recruitment. But n o single factor alone caused changes in vital rates of age-0 fish that could account for the 145-fold variability in the Potomac River index of juvenile recruitment. However, combined positive or negative effec ts of two or more factors resulted in more than a 150-fold simulated r ecruitment variability. suggesting that combinations of factors can ac count for the high observed annual variability in striped bass recruit ment success. Higher cumulative mortality of feeding larvae and younge r life stages than of juveniles was common to all simulations, support ing the contention that striped bass year-class strength is determined prior to metamorphosis.