Use of size‐dependent mortality models to estimate reductions in fish populations resulting from toxicant exposure

In populations in which the rate of early mortality depends primarily on the size of individuals, growth and size become important determinants of population dynamics. Models based on size and developed for fish populations can provide a means of integrating acute and chronic toxicological observations to predict changes in population size. These models predict population reductions resulting from lethality to eggs and larvae, reduced growth rate, reduced length at hatch and any behavioral or physiological changes that increase either size‐dependent or size‐independent mortality rates. The dependence of mortality rate on size may arise from developmental changes, size‐selective predation, changing energy balances or a combination of these. The biological source of mortality may dictate its mathematical expression. Since the size‐dependent mortality modeled here may arise from several common sources, it may be widespread. As a result, reductions in natural populations caused by sublethal toxic exposures may not be unusual. These results suggest that measuring sublethal reductions in early growth that result from toxic conditions may be a meaningful way of estimating potential risks to natural populations.