A Computer Simulation of the Effects of Superimposed Mortality Due to Pollutants on Populations of Fathead Minnows (Pimephales promelas)
This computer simulation study tested the effects of 99 levels of proportional mortality on fathead minnow (Pimephales promelas) populations, assuming that the parent–progeny relationship is of the form proposed by Ricker. Limited data from two studies on three lakes were available to fit the model and obtain estimates of parameters for fathead minnow populations. Based on these estimates, 25 replications of a 50-generation cycle were simulated under two levels of environmental variability. Arbitrary extinction levels of 5, 100, and 500 females had little effect on the results. Increasing environmental variation lowered the percentage mortality at which population extinctions occurred. In general, the results are compatible with the recommendation of the U.S. Committee on Water Quality Criteria, that the maximum concentration of zinc to which fish could be continuously exposed should not exceed [Formula: see text] the 96-hr TLm (median tolerance limit) — a concentration that caused a 50% reduction in the mean number of eggs laid per female by fathead minnows in a laboratory study.