Confronting Change in a Critical Fishery

By Carolyn Rumery Betz

Few Wisconsin wildlife species are more sensitive to changes in their environment than trout. They depend on a particular set of conditions to survive, including a narrow range of cold water temperatures. Climate change poses an extraordinary challenge to this critical state resource.

Brook Trout Mitro Photo

Department of Natural Resources researchers John Lyons and Matthew Mitro have spent years studying the impacts of environmental change on 50 fish species in Wisconsin. They track how things like changes in land use, stream characteristics and warming temperatures affect fish populations.

For Lyons and Mitro, high quality climate information, scaled to local conditions across Wisconsin, is extraordinarily valuable to help monitor the state's trout fisheries. Thanks to WICCI, they're getting the data they need from atmospheric scientists at the University of Wisconsin-Madison's Nelson Institute Center for Climatic Research.

The fish researchers and climate scientists met in 2007 as WICCI was being co-organized by the Nelson Institute and the Department of Natural Resources.

"This was the opportunity our climate group was looking for,"says Dan Vimont, who with Chris Kucharik, co-leads the WICCI Climate Working Group. "The data we generated would be especially useful when applied to real-life issues. Impact on trout was the perfect first application."

The Coldwater Fish and Fisheries Working Group was the first of WICCI's 16 working groups to form. Twenty-one biologists from the Department of Natural Resources, U.S. Geological Survey, University of Wisconsin System and Trout Unlimited comprise the group.

Driftless Area Southwest Wisconsin_Betz

Incorporating Wisconsin specific climate data in the fish researchers' models produced startling results: all but four of 50 species they studied would be affected. About half of them, warmwater species such as bass, could benefit from the change. But coldwater species are at risk as air and water temperatures increase. Brown trout and wild brook trout in particular have narrow temperature ranges in which they can successfully live, feed and reproduce.

Under the most extreme summer warming conditions projected by the models — where air temperatures would increase by about 9°F and water temperatures by 7.2°F — brook trout may not survive in Wisconsin at all, and brown trout may decrease by 88 percent. Even under more moderate conditions of air temperature increasing by 1.8˚F and water temperature by 0.8˚F, brook trout distributions may shrink by 44 percent and brown trout by 8 percent.

Temperature change by itself does not predict the presence or absence of fish, according to the researchers, but they say subtle effects on the life cycles or growth patterns of trout can trigger their demise.

"Trout have an optimal temperature range for feeding and growth," says Mitro, who leads the WICCI working group. "When they are forced to spend time outside that optimal range, they may not be feeding as much as when the temperatures are more suitable and when more oxygen is present. This stress affects egg production and egg development."

The Coldwater Fish and Fisheries group suggested two adaptation strategies to reduce the impact of climate warming on trout. One is to use a triage approach to identify and allocate management resources to only those coldwater streams where the fish are most likely to succeed. That could include managing for brown rather than brook trout. The second strategy is to develop activities focusing on land, shoreline, water management and instream restoration to offset the impacts of rising air and water temperatures and changes in precipitation.

The Department of Natural Resources is heeding these recommendations for the Driftless Area, a 23-county region in southwestern Wisconsin that holds the highest concentration of trout waters in the state.

The researchers are working with fish biologists and land managers to develop a 15-year master plan for thousands of acres the agency owns and manages for habitat and to provide public access to streams.

"The Driftless Area Master Plan is an excellent example of how we are using science and technology to drive strategic planning efforts," says Allen Shea, DNR's director of the Office of Business Support and Sustainability.

Fisheries ecologist Paul Cunningham co-leads the planning effort. "We're at a decision-making point of where to spend limited land acquisition dollars and our fish biologists' time," he says. "Should we focus on the limited reserves for native brook trout, or should we put our effort on brown trout that are predicted to better cope with warmer temperatures?"

The agency is seeking public input on these decisions. The plan will be completed in 2014.

Advantage: parasites?

Gill lice are tiny parasites that infect only brook trout, causing gill deformities that impair the fishes' ability to obtain sufficient oxygen and release carbon dioxide, ammonia and other byproducts.

Since gill lice reproduce more frequently in warm water, increased air and water temperatures may increase their opportunity to infect brook trout. On Tenny Spring Creek in Vernon County, fish research biologist Matthew Mitro observed in June 2012 that 12 percent of the brook trout were infected. By September, 26 percent were infected, and by November, 39 percent. Mitro has not found the same pattern in other streams, so he is trying to determine why some streams see an increasing infection rate while others do not.

Brook trout anglers can help track the presence or absence of gill lice through a citizen science collaboration between the Department of Natural Resources, Wisconsin Trout Unlimited and River Alliance of Wisconsin. Anglers can use an on-line reporting form ( to submit their observations. A paper form is also available through Wisconsin Trout Unlimited. Whether or not gill lice are present, anglers should disinfect their gear with a bleach solution prior to fishing in the next stream to prevent the potential spread of parasites, invasive species and diseases.