No abstract

Four decades of observations on the limnology and fishes of Oneida Lake, New York, USA, provided an opportunity to investigate causes of mortality during winter, a period of resource scarcity for most juvenile fishes, in age-0 yellow perch (Perca flavescens) and age-0 white perch (Morone americana). This time series contains several environmental (e.g., winter severity) and biological (e.g., predator abundance) signals that can be used to disentangle multiple effects on overwinter mortality of these fishes. A multiple regression analysis indicated that age-0 yellow perch winter mortality was inversely related to fish length in autumn and to the abundance of alternative prey (gizzard shad [Dorosoma cepedianum] and white perch). However, no length-selective predation of yellow perch by one of the main predators, adult walleye (Sander vitreus), was detected. In contrast, white perch mortality was directly associated with total predator biomass and abundance of white perch in autumn, and inversely related to yellow perch abundance as a potential buffer species, but not to the abundance of gizzard shad. Winter severity was not a significant predictor of mortality for either perch species. Predicted winter starvation mortality, from a model described in the literature, was much lower than observed mortality for yellow perch. Similar models for white perch were correlated with observed mortality. These results collectively suggest that predation is the main mechanism shaping winter mortality of yellow perch, while both predation and starvation may be important for white perch. This analysis also revealed that gizzard shad buffer winter mortality of yellow perch. Although winter duration determines the northern limit of fish distributions, in mid-latitude Oneida Lake and for these species, predator-prey interactions seem to exert a greater influence on winter mortality than starvation.

We 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.