Effects of hypolimnetic hypoxia on foraging and distributions of Lake Erie yellow perch

Abstract

Bottom hypoxia (< 2 mg O 2 L − 1 ) is a widespread phenomenon in marine and freshwater systems, yet the ecological consequences of hypoxia are generally unknown, especially for mobile organisms such as fish. Herein, we explore how a large area of hypolimnetic (i.e., sub-thermocline) hypoxia that develops seasonally in Lake Erie's central basin influences yellow perch ( Perca flavescens), a demersal species of both ecological and economic importance. We hypothesized that hypolimnetic hypoxia would negatively affect yellow perch by limiting access to benthic prey and preferred (cool) temperatures. To explore how hypoxia influences yellow perch foraging and migration patterns in central Lake Erie, we collected a suite of biological (i.e., fish with bottom and mid-water trawls, benthic macroinvertebrates using Ponar grabs, and zooplankton via depth-specific pumping) and physical (i.e., temperature and dissolved oxygen) data monthly during June through October 2005. Our results indicate that yellow perch avoid hypoxic bottom waters by either moving horizontally away from the hypoxic zone or migrating above the oxycline. We also found evidence to suggest that individuals that moved above the hypoxic hypolimnetic layer continue to “dive” into the hypoxic layer to feed on benthic invertebrates. Even so, during the height of hypoxia, both the amount and proportion of benthic macroinvertebrates consumed decreased, whereas consumption of zooplankton increased. While hypoxia-induced changes in yellow perch distributions and foraging likely affect individual condition and growth in the short-term, the long-term effects on population production remain equivocal.