| Hypoxia (<2 mg O2·L-1) is a widespread phenomenon in marine and freshwater systems worldwide, yet the ecological consequences of hypoxia are generally unknown, especially for mobile species such as fish. Areas of hypoxic conditions or "dead zones", due primarily to eutrophication (i.e. nutrient enrichment), are viewed as a major threat to aquatic ecosystem function worldwide. Areas of bottom water (hypolimnetic) hypoxia have long been documented and are increasing in the Lake Erie ecosystem, an economically and ecologically important water body within the Laurentian Great Lakes. Quantifying the ecological consequences of hypoxia for highly mobile organisms (e.g., yellow perch Perca flavescens) is a complex task. Such organisms are capable of avoiding direct lethal effects of hypolimnetic hypoxia, but may be indirectly affected as they are forced to occupy inferior habitats (i.e., novel prey, predators, competitors and physical conditions). I used field, and laboratory techniques to address the overall hypothesis that hypolimnetic hypoxia in Lake Erie negatively affects yellow perch.Laboratory results suggest yellow perch growth and consumption are negatively affected by low oxygen conditions. However, my field results suggest yellow perch attempt to mitigate these potential consequences by altering their distribution and foraging patterns in the presence of hypoxic conditions. My results also suggest a change in the sub-daily behaviors of yellow perch. This behavioral change involves short-term forays to forage within hypoxic habitats. The largest consequence of hypoxia for yellow perch in LECB is altered distribution patterns due to vertical or horizontal migrations in avoidance of low oxygen conditions. Overall, it appears hypoxia has the potential to negatively affect yellow perch however, behavioral modifications allow yellow perch to mitigate the extent of these consequences in Lake Erie. These results will have management implications for Lake Erie resource agencies and provide important conclusions concerning the ecological consequences of hypoxia for freshwater fishes. |
