Modeling Growth and Survival in an Age-0 Fish Cohort

Abstract

We applied an individual-based model to an age-0 cohort of smallmouth bass Micropterus dolomieu to simulate the cohortˈs growth and survivorship through its first growing season. The purpose was to determine whether the stock–recruitment characteristics of the age-0 fish could be predicted. The model smallmouth bass were exposed to size-dependent predation, size-independent mortality, and starvation mortality resulting from depletion of their prey supply. Survivorship curves were produced by model simulations. When survivorship at a given time was plotted against initial egg density during the early growing season, the curve resembled the peaked pattern of a Ricker-type curve. In contrast, curves for survivorship during the late growing season had no noticeable peak or maximum. Other results showed (1) strong density dependence of the mortality rate early in the growing season and density independence late in the growing season; (2) a distinct critical time (CT) during 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 initial egg density. Competition for and overexploitation of prey during the early growing season produced these results. The model simulation results resembled patterns of some empirical data.