Predicted effects of water temperature increases on the distribution of warmwater 
fishes in Wisconsin streams and rivers
John Lyons*, Wisconsin Department of Natural Resources, WI  

Global climate change will cause Wisconsin streams and rivers to become warmer over the 
next 50 years, although the magnitude of the temperature increase is uncertain. Some 
warmwater fishes, preferring summer water temperatures above 21 C, are likely to expand 
their distribution. I used a recently developed GIS-based watershed model to predict the 
occurrence of 50 warmwater species across all 90,000 km of streams and rivers in 
Wisconsin under several different warming scenarios. Presently, 13,000 km, mainly small 
headwaters, are estimated to be too cold for warmwater fishes. Under the largest modeled 
water temperature increase, 3 C, these coldwater habitats are predicted to decline by 95%, 
whereas under the smallest, 1 C, the decline will be about 50%. Widespread warmwater 
species adapted for headwaters, such as creek chub, fathead minnow, and johnny darter, 
are expected to expand their distributions into most of the stream reaches that are no longer 
coldwater. Less widely distributed headwater species, such as southern redbelly dace, will 
show much smaller expansions because they will be prevented by dams and unsuitable 
habitat (lakes, large rivers) from accessing much of the former coldwater habitat. Species 
preferring larger streams and rivers, including many catostomids (e.g. shorthead redhorse), 
centrarchids (e.g., smallmouth bass), and percids (e.g., logperch) will show little change in 
distribution because they are unsuited to headwater habitats. Under the largest temperature 
increase, some species, notably walleye, may actually decline in distribution as some large 
rivers, the warmest habitats in the state, become too warm for them. Although many 
Wisconsin warmwater stream species are predicted to have relatively little change in 
distribution from stream warming, global climate change may nonetheless have major 
effects on their populations through milder winters, earlier spawning periods, expanded 
growing seasons, and changes in community dynamics.
*Presenter