Does hypoxia reduce habitat quality for Lake Erie walleye (Sander vitreus)? A bioenergetics perspective

In Lake Erie, the duration and extent of hypoxia (dissolved oxygen (DO) <= 2 mg.L(-1)) has increased in recent years, yet little is known on the corresponding impact on its fish, particularly the highly valued walleye (Sander vitreus) fishery. Here, we quantified the impact of hypoxia on walleye habitat quality, using a spatially explicit growth rate potential (GRP) modeling approach, which integrates the spatial arrangement of biological (prey availability) and environmental (DO, temperature, irradiance) measures. Data were collected along two types of transects: 60 km north-south transects (each sampled once during day and night) and 5 km east-west transects (sampled every 4 h for 24 h) during August (pre-hypoxia), September (peak-hypoxia), and October (post-hypoxia) 2005. Overall, the average monthly amount of high quality habitat (GRP > 0 g.g(-1).day(-1)) for walleye declined slightly with hypoxia (<2.0%); however, hypoxia appeared to enhance habitat quality by concentrating prey in favorable temperature, DO, and light conditions. In September, percentages of walleye growth rates were at the upper end of the range, much more so than during August or October. Although an understanding of walleye distributions, foraging, and growth in relation to hypoxia is needed, our results do not suggest that hypoxia is negatively influencing walleye through reduced habitat quality.