Modeling Impacts of Hypoxia on Lake Erie Fishes

The following provides a quick snapshot of key findings.  A more in-depth discussion and references to the scientific literature can be found here.

While empirical evidence points to a variety of negative and positive effects of hypoxia on different fish species the magnitude of those effects consequences remains an open question and on we explored through models.  We found a significant negative relationship between the number of hypoxic days and the condition of yellow perch, suggesting that hypoxic during summer may have population-level impacts.

regression

We also modeled growth rate potential (GRP) of selected fishes as a surrogate of fish habitat quality. While hypoxia had a temporary positive effect on walleye GRP because prey fish were forced into areas favorable for efficient walleye foraging and growth, yellow perch, rainbow smelt, emerald shiner, and round Goby GRP improved with reductions in hypoxia prior to the mid-1990s, but did not continue to improve from the mid-1990s through 2005 (and may even have decreased).

Hypoxia-climate interactionsWhile warm-water, cool-water, and even some cold-water fishes could benefit from warmer waters, longer growing seasons, and increased over-winter survival, this may not hold for cool- and cold-water fishes under increased intensity and duration of hypoxia.

Output from a bioenergetics-based GRP model comparing a relatively warm year with prolonged and extensive hypoxia to a relatively cool year with a thin hypoxic layer persisting for a short time, we showed that climate warming can cause preferred habitat to be squeezed both from above (by warmer temperatures) and from below (via increased hypoxia).

side by side squeeze

In general, this “thermo-oxy squeeze” can be troubling for key fish species.Fish Squeeze