“The two best times to fish is when it’s rainin’ and when it ain’t,” said humorist Patrick MacManus. Wisconsin’s 230,000 anglers feel the same way. The state’s 10,266 miles of trout streams—40% of them rated high-quality—are home to some of the best trout fishing in the U.S. The conservation organization Trout Unlimited singles out Wisconsin’s trout management programs as “an example of habitat stewardship that other states should emulate.” In particular, the Driftless Area—an unglaciated landscape found in southwest Wisconsin, southeast Minnesota, northeast Iowa and northwest Illinois--offers some of the best trout fishing opportunities in the state. A report commissioned by Trout Unlimited found that recreational angling in the Driftless Area generates $1.1 billion annually. In addition to economic benefits, trout fishing has bred its own culture, especially amongst those who cast hand-tied flies into the currents and wait in anticipation to hear that sucking sound of a “fish on.”
How will climate change affect fly fishing in the Driftless Area? Researchers at the University of Wisconsin-Madison predict that the Driftless Area can expect a 6 °F (3.3 °C) increase in annual average temperatures by 2055, with a 5.6 °F (3.1 °C) and 6.3 °F (3.5 °C) increase in average annual highs and lows, respectively. The predicted increase in average annual surface air temperatures will in turn increase stream water temperatures to some degree. However, some streams will likely be able to buffer the warming effect by an increase in groundwater flow from predicted increases in precipitation. In streams that do not have a buffering capacity, the increase in water temperature could lead to stress in species adapted to cooler water. Other warmer-water species may be able to exploit areas previously out of their thermal range or previously dominated by the cooler-water species. In essence, some fish will be "winners" and others "losers" in the face of climate change.
Trout are cold-water species, requiring clear, cool water, high dissolved oxygen levels, and vegetative cover to protect young from predation. Slight changes in these habitat variables can cause stress on the different species of trout and potentially lead to local extinction. One of the most popular trout species for anglers, the brook trout, Salvelinus fontinalis, is more sensitive to warmer waters than the brown trout, Salmo trutta, or rainbow trout, Onchoryncus mykiss. According to research done by the Wisconsin Department of Natural Resources, a water temperature increase of 1.8 °F (1 °C) would reduce the current brook trout range by roughly 78%, and an increase of 5.4 °F (3 °C) by 98%, effectively eliminating the brook trout from a vast majority of the Driftless Area streams. Alternatively, the 1.8 °F increase in temperature would actually expand the brown trout range by 28%, but the 5.4 °F increase would reduce it by 83%. These species highlight how climate change could interact with differences in physiology to create new suites of species in Wisconsin’s ecosystems.
In addition to changes in temperature, researchers also expect that precipitation events will be more variable and severe. Flood events dramatically alter fish habitat through sedimentation, physical scouring, and shoreline erosion. An increase in flood events would also likely reduce the number of days suitable for trout fishing—even for fishermen as hardy as Patrick MacManus.