Growth, condition, and diets of age-0 Saginaw Bay yellow perch: Implications for recruitment

Yellow perch (Perca flavescens) constitute populations of economic and ecological importance throughout the Laurentian Great Lakes Region, but these populations are often subject to substantial recruitment variability. In Saginaw Bay, Lake Huron, annual monitoring indicates that during recent years age-0 yellow perch experienced relatively high survival during early life. The collapse of the Lake Huron alewife population may have contributed to this phenomenon by leading to reduced larval yellow perch mortality in Saginaw Bay. However, recent high age-0 yellow perch production has been accompanied by reduced sizes of young perch (perhaps due to increased intraspecific competition) and low recruitment to adult stages. Low sampling frequency (i.e. once per year) has previously limited a rigorous evaluation of the mechanisms underlying poor perch recruitment in Saginaw Bay. Additionally, the extent to which other recent changes in the Saginaw Bay ecosystem have influenced yellow perch foraging, growth, and subsequent survival remained unstudied. With the goal of understanding early-life dynamics of yellow perch, we conducted frequent sampling and tracked growth, consumption, and condition of two yellow perch cohorts from larval stages through the first year of life. Additionally, we examined variation in age-0 yellow perch diet patterns and related foraging strategies of age-0 yellow perch to environmental variables. Mortality of young yellow perch is closely tied to growth: we observed consistent size-selective predation by the primary piscivores in Saginaw Bay (walleye, Sander vitreus), and we found significant increases in length and decreases in total energy content of young yellow perch following the first winter of life. Growth in length, mass, and total energy all slowed during late summer and early fall for both cohorts of age-0 yellow perch, prior to drastic reductions in temperature. Age-0 yellow perch consumed primarily zooplankton, and variation in diet variables across sites was greater than variation over time or ontogeny. Additionally, among-individual specialization was occasionally an important component of population foraging niches. After accounting for densities of available prey, diet selectivity indices were highest for Daphnia spp. and Chironomidae larvae. Furthermore, foraging patterns by young yellow perch appeared to respond to ambient densities of Daphnia spp., Chironomidae larvae, and Dreissena spp. Mussels; the latter of which was correlated with reduced consumption of benthic prey items. Recent changes in the Saginaw Bay foodweb play an important role in diets, growth, and recruitment of yellow perch