A Simulation Model of How Life History Strategies Mediate Pollution Effects on Fish Populations

Abstract

Pollution effects on fish populations were estimated with a simulation model, using Leslie matrices. Results from changing only first-year survival rate (So) have already been published (Schaaf et al. 1987). This paper explores the effects of perturbing both So and the adult survival rate (Si) for 12 spatial-temporal stocks. Most stocks examined are more sensitive to permanent change in Si than to changes in So. The relative importance of these two rates in determining the population growth rate (λ) depends upon the age distribution of the expected lifetime egg production of age i females (Vi). In turn, the vector Vi, as measured by its mean and standard deviation, is shown to vary among geographic or temporal stocks of a single species. Hence, we quantify the impact on population size of destroying a fixed percentage of habitat, relative to where and when it occurs (i.e., relative impact on Si and So). For example, destroying 1% of the Atlantic menhaden habitat would reduce λ by 0.8% and the population by 8.0% in 10 yr, if the impact affected only adults (e.g., offshore in winter). If the 1% habitat destruction all occurred in the estuaries, affecting juveniles as well, λ would be reduced by almost 5%, and in 10 yr drive the population down to 58% of its former equilibrium. We show that knowledge of the mean and variance of the age distribution of Vi permits prediction of relative sensitivity among species to pollution. Within species, this knowledge of Vi permits comparison of the effects of impacting different life stages and at different times and places.