University of Minnesota researchers work to secure the future of trout

Len Ferrington has one eye on the weather and the other on Minnesota House File 3352.

The longtime University of Minnesota entomology professor is awaiting approval of a $400,000 grant to continue the last segment of a study that's been going on for a dozen years into the different growth rates of trout in the Driftless Area of southeastern Minnesota.

The future of trout fishing in the region faces a dire threat from climate change, and Ferrington and his students are trying to understand the trout life cycle to help develop management strategies to conserve the genetic and biological diversity of the fish and the insects they feed on.

The Minnesota Department of Natural Resources has considerable information on trout growth between spring and fall of any given year, but their winter maturation is less understood, Ferrington said. DNR researchers know that in some streams in the southeast, trout grow quickly, while in others, their growth is marginal or they even lose weight, he said.

"So what we're trying to figure out is, is part of this related to diet?" he said.

In previous years, Ferrington and his team of two to five students have slogged through icy streams to study mostly brown trout and the insects they favor in winter: stoneflies and non-biting midges. They noticed that the insect population relates to the amount of groundwater entering the stream.

The Driftless Area takes its name from the fact that it was largely bypassed by glaciers, so there was little "glacial drift," or sediment, left behind. Streams in the area are fed in part through limestone springs that send water to the surface at about 48 degrees Fahrenheit. That keeps the trout cold in the summer and warm in the winter.

"So the more groundwater, basically, the warmer they are in the winter. It translates to more aquatic insects and higher growth rates for aquatic insects, which then provide food for the trout," said Ferrington, who runs the U's Chironomidae Research Group, named for the midges they study.

The trout streams they've studied have more than two dozen species of insects that grow only in winter. Some can suppress their freezing point to about 16 below, Ferrington said. In the summer, he said, they burrow into the streambeds to keep cool.

Research shows that streams in southeast Minnesota are affected by air temperatures and human activities such as farming, according to one of Ferrington's presentations on the subject. That makes them ideal for studying the effects of global warming on resources valued for their economic, sport and aesthetic contributions.

If the climate continues to warm, Ferrington said, eventually the insects will disappear, and so will the trout. He cited a model for Wisconsin that includes dire predictions for brook trout in the state over the next 50 years.

Solutions to protect trout streams from global warming would take a long time to develop and deploy. So what are the practical applications that derive from Ferrington's research?

"We also notice that the way in which vegetation around the streams is arranged can, to some degree, help promote the kinds of aquatic insects that are growing in the stream," Ferrington said. "The riparian buffers really are important in the trout streams."

The study has used funds from a variety of sources over the years. The money for this last leg, assuming it's approved, would come from the Legislative-Citizen Commission on Minnesota Resources. When completed in a few years, Ferrington said, he expects it will be used to determine which trout steams are the best targets for conservation measures.

@browningSTRIB • 612-673-4493