MODELING GROWTH AND SURVIVAL IN AN AGE-0 FISH COHORT

We applied an individual-based model to an age-0 cohort of smallmouth bass Micropterus dolomieu to simulate the cohort's growth and survivor ship through its first growing season. The purpose was to determine wh ether the stock-recruitment characteristics of the age-0 fish could be predicted. The model smallmouth bass were exposed to size-dependent p redation, size-independent mortality, and starvation mortality resulti ng from depletion of their prey supply. Survivorship curves were produ ced by model simulations. When survivorship at a given time was plotte d against initial egg density during the early growing season, the cur ve resembled the peaked pattern of a Ricker-type curve. In contrast, c urves for survivorship during the late growing season had no noticeabl e peak or maximum. Other results showed (1) strong density dependence of the mortality rate early in the growing season and density independ ence late in the growing season; (2) a distinct critical time (CT) dur ing which the slope of the survivorship curve changed from a steep to a shallow decline, and (3) a decrease in CT as a function of the initi al egg density. Competition for and overexploitation of prey during th e early growing season produced these results. The model simulation re sults resembled patterns of some empirical data.