Depensatory Mortality, Density‐Dependent Growth, and Delayed Compensation: Disentangling the Interplay of Mortality, Growth, and Density during Early Life Stages of Yellow Perch

Abstract

AbstractWe present long‐term (>40‐year) patterns in the density of age‐0 yellow perch Perca flavescens in Oneida Lake at four early life stages (at egg deposition, at the attainment of a total length of 18 mm, on 1 August, and on 15 October), from which we calculated mortality and growth rates during the three intervals between these early life stages. At each of these stages, age‐0 yellow perch densities have been lower in recent years than in the 1960s and 1970s. Mortality rates showed no time trend from egg to 18 mm (interval 1 [the larval stage]), increased from 18 mm to 1 August (interval 2 [the limnetic stage]), and decreased from 1 August to 15 October (interval 3 [the demersal stage]). We also tested previous hypotheses for density‐dependent effects on mortality and growth using the entire long‐term data set. Contrary to expectations from the 1960s, the mortality rates of age‐0 yellow perch in Oneida Lake are no longer depensatory. Overall, the growth rate of age‐0 yellow perch has increased over time and become density dependent. Also contrary to common expectations of size‐selective mortality, greater average total length is not associated with decreased instantaneous daily mortality for two early life stage intervals. The combined effect has been a decline in age‐0 yellow perch density and an increase in average total length by the end of their first year. Although increased growth has not sufficiently compensated for increased mortality during the first year of life, obtaining a larger end‐of‐year size should reduce subsequent mortality during the winter period, providing for a process of delayed compensation that helps stabilize density at age 1.