Yellow Perch within Lake Erie's Central Basin must contend with the development of hypolimnetic hypoxia, which generally occurs August - October and reaches thicknesses of up to 8 meters off the lake bottom. Since Yellow Perch are primarily demersal benthivores, large portions of their primary habitat becomes unsuitable during hypoxic events. Field studies have shown that while Yellow Perch largely avoid hypoxia, they continue to forage for benthic prey despite hypoxic conditions. Little is known about the fine-scale behavioral changes of Yellow Perch during hypoxia, or the physiological consequences of hypoxic foraging. In controlled laboratory experiments, I analyzed the behavioral changes of Yellow Perch under simulated hypolimnetic hypoxia, and determined the physiological response of Yellow Perch to hypoxic exposure by measuring the response of a hypoxia-responsive protein, Hypoxic Inducible Factor-1-alpha (HIF-1a).
Yellow Perch were subjected to normoxic (~8 mg DO/L), moderate hypoxic (~4 mg DO/L) or severe hypoxic (~2 mg DO/L) dissolved oxygen concentrations for durations of up to 8 hours, followed by a 40-hour normoxic recovery period. Baseline HIF-1a levels were detected in Yellow Perch liver tissues under normoxic conditions, and increased significantly after two hours of hypoxic exposure. HIF-1a peaked at 2 and 4 hours of hypoxic exposure under severe and moderate hypoxic conditions, respectively, but returned to levels similar to normoxic treatments by 8 hours of exposure. These results suggest Yellow Perch are well adapted to hypoxic conditions and that a direct negative feedback mechanism may aide survival under prolonged hypoxia.
In order to observe the behavioral changes of Yellow Perch in stratified hypoxic conditions, I designed and constructed two experimental tank systems that simulated hypoxic conditions characteristic of temperate freshwater lakes. Using these systems, two behavioral experiments were conducted examining changes in behavior and consumption of Yellow Perch subjected to various thicknesses of hypolimnetic hypoxia. While the number of hypolimnetic forays did not differ between hypoxic and normoxic treatments, dive duration decreased significantly during hypoxia, resulting in less time total time in the hypolimnion. Consumption did not significantly decrease until hypoxic thickness reached 4.0 meters. These findings suggest that the ability of Yellow Perch to forage benthically is not greatly affected by hypoxia less than 2.6 meters in thickness; however, increasing hypoxic thickness likely decreases the energetic gain of benthic foraging, driving horizontal shifts in Yellow Perch populations to areas where hypoxia is thinner (< 2.6 m). Increases in the duration or spatial extent of hypoxia resulting from forecasted global climate conditions are likely to lead to further changes in community distributions, increased competition, and altered trophic interactions.