Great Lakes Wisconsin Fish

Great Lakes Communities and Ecosystems at RiskThe Region 

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Climate Change in Wisconsin
Leopard Frog
Introduction
Climate Projections
Agriculture
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Human Health
Lakes, Streams, & Fish
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Climate Change Impacts:
Lakes, Streams, and Fish

Wisconsin's numerous lakes, rivers, and streams draw millions of visitors each year. Canoeing, fishing, hiking, and bird watching are among the many activities of these visitors. Aquatic ecosystems, and species that depend on them, will be impacted by a warmer climate, land-use changess, and the introduction of invasive species.

Native aquatic plant and animal species will differ widely in their responses to changing water temperature and hydrology. Some will respond by adapting to warmer temperatures, or expanding their ranges northward, or seeking refuge in areas where temperatures and flow patterns remain suitable. Others will decline to extinction. Among the projected impacts are:

  • A Change in the Distribution of Fish Species
    Individual fish actively select and rapidly change living areas based on suitable temperatures, oxygen concentrations, and food availability. As water temperatures in the region increase, cold-water species, such as lake trout, brook trout, and whitefish, may decline dramatically as cool-water species, such as muskie and walleye, along with warm-water species, such as bluegill and smallmouth bass, expand their ranges northward. As a result of these changes, anglers may lose their preferred catch. To compensate for range and population changes, current stocking methods may need to be reevaluated.

  • The Spread of Invasive Species
    A changing climate will likely favor invasive species with generalized habitat and feeding requirements over native species with more specialized needs. The spread of non-native nuisance species will likely compound the impacts of climate change on Wisconsin's aquatic ecosystems. Climate change is likely to permit zebra mussels and common carp to expand their range northward. Their movement, along with the introduction and spread of other invasive species and climate change, will fundamentally change native fish communities.

  • An Increase in Summer Stratification
    Stratification of lakes occurs when a warm surface layer of water develops over cooler, deeper water. A warming climate increases the duration of summer stratification in the deep lakes. This, in turn, makes frequent and larger "dead zones"—areas of water depleted of oxygen and unable to support life—more likely. Persistent dead zones can result in toxic algal blooms, foul-smelling, musty-tasting drinking water, damage to fisheries, and massive fish kills—known as "summerkill".

  • Loss of Winter Ice
    Declines in the duration of winter ice on lakes are expected to continue. The loss of winter ice may be a mixed blessing for fish, reducing winterkill from oxygen deficits in shallow lakes but also jeopardizing reproduction of whitefish in the Great Lakes bays, where ice cover protects the eggs from winter storm disturbance.

  • The Release of Nutrients and Contaminants
    Lower oxygen and warmer temperatures promote greater microbial decomposition and subsequent release of nutrients and contaminants from bottom sediments. Phosphorus release would be enhanced, and mercury release and uptake by biota would also likely increase—exposing humans to higher mercury levels via fish consumption.





Photo Credits:
Leopard Frog -- John Maguson.
Door County Lakeshore -- Karen Holland (Courtesy of USEPA)

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