If you ask a Wisconsin trout fisherman about the condition of the state's trout population, you're likely to bring a smile to his or her face. "There's more streams than you could probably fish in a lifetime," trout enthusiast Dave Fowler tells me when asked about his fishing domain in southwestern Wisconsin. "Just from talking to people who fish more than I do…they can definitely tell the difference."
There's no doubt Wisconsin's trout population is in good shape. The state is home to more than 10,000 miles of trout streams, and biologists estimate there haven't been this many stream trout in the state in 150 years. Dane County has its share, with public trout fishing areas at the West Branch Sugar River Watershed, Gordon Creek Watershed and Black Earth Creek Watershed.
But the future for these coldwater fish looks bleak.
The brook trout and brown trout - Wisconsin's two common stream-dwelling chars, to use their technical classification - cannot survive if water temperatures creep into the mid-70s. Obviously, this is not a problem during Wisconsin's cold winters and cool springs and falls, but anyone who has spent a summer in the state could tell you how hot it can get in July and August. This is nice for swimmers and sunbathers, but for anglers like Fowler, rising temperatures mean fewer trout habitats to fish.
With air temperatures on the rise due to climate change, stream temperatures are sure to heat up too. A 2011 report by the Wisconsin Initiative on Climate Change Impacts (WICCI) estimates rising stream temperatures could push trout populations to the brink of extirpation in as few as 50 years in a worst-case scenario.
If water temperatures increase by 7.2 degrees Fahrenheit (a worst-case scenario), WICCI estimates all Wisconsin streams will be too warm for brook trout, and 88.2% of them will be too warm for brown trout, which are hardier in warm water.
As bad as that sounds, it's not time to lose all hope just yet.
John Magnuson, who has researched freshwater habitats at the University of Wisconsin-Madison for several decades, urges me to choose my words carefully when I ask him how serious the situation is.
"What you cannot say, and what we would never say, is that this is what's going to happen," Magnuson says. "These are not predictions. One of the things we have to tell people over and over again in these scenarios [is that] these are among the expected results."
The models constructed for the WICCI report, which also projects moderate- and best-case scenarios, do not account for other results of climate change like variations in precipitation or groundwater input, both of which could help cool streams. Nor do they account for human initiatives, such as better land-use practices, reduction of carbon dependency or other local conservation efforts.
Matt Mitro, a freshwater scientist who works for the Wisconsin Department of Natural Resources and is a coauthor of the WICCI report, tells me the models in the report are only a starting point. WICCI plans to incorporate controls for other factors in stream water temperature in future modeling, but for now, Mitro says, they at least provide a rough estimate of how trout streams will look in the future.
"[The models] were originally created to look at, based on landscape characteristics and climate variables, any stream segment across the state and predict whether different fish species would be present or absent in those locations [in the future]. It kind of gives us an overall picture of where trout can be found in the state," Mitro says.
Trout flourished in Wisconsin until the early 20th century, when poor land-use practices and pollution degraded streams and destroyed trout habitats. But thanks to restoration efforts from the DNR and other conservation agencies, the state's streams are better suited for trout than they have been in a long time.
"Our trout populations have rebounded, and they're more common than they were 50 to 100 years ago, and more numerous as well," says John Lyons, another freshwater fish scientist at the DNR and a coauthor of the WICCI report. "That doesn't mean they're completely everywhere where they were or completely returned to where they were, say, 200 years ago, but they're doing as good as they've been in the last century now as a whole."
But Lyons knows as well as anyone the good times may not last for trout fishermen like Fowler. The most recent estimates from scientists who study the Earth's warming trends suggest the planet's surface is on track to heat up by more than six degrees by 2100. This estimate is so far in the future that it's tough to get a grasp on just how accurate it is, but a warming of this magnitude in Wisconsin could be catastrophic for the state's trout population.
To help mitigate the threat, conservation groups use several tactics. Streams with wide banks and shallow depths warm up more easily. By deepening and narrowing streams, particularly those with eroded banks, scientists hope to cool water temperatures. Removing beaver dams, which slow the flow of streams and therefore warm the water, also helps.
Each of the stream experts I spoke with also emphasized the importance of classifying and triaging streams. Some streams are already so close to being too warm for trout in the summer that any mitigation efforts would likely be a waste of resources. Others are so cold that moderate increases in air temperature are unlikely to affect their trout populations. A third group of streams falls in between the other two. This is where the scientists would like to focus their energy.
"One of our goals is to more precisely identify streams where you might be able to make a difference, where you could do some things that would change the outcome," says Lyons.
The scientists are divided on the condition of Wisconsin's trout population in the long term. Mitro describes himself as optimistic about the situation, citing federal and state stream restoration efforts as reasons to be hopeful.
Lyons is less sanguine.
"Even with our best efforts," he says, "with very focused and efficient activities, I think we're going to lose a lot of trout streams. Perhaps the vast majority of them, if things are extreme enough."
Over the next 100 years, Lyons adds, "I think it's almost certain that there's going to be some major decline unless there's some radical reorientation of the world economy, world trends and greenhouse gas emissions, which doesn't seem to be on the horizon right now. In that kind of a timeframe, I'm pretty pessimistic."