February 22, 2011
60 years of survey records show more fish overall, and in all sizes examined
STEVENS POINT -- Wisconsin brook and brown trout populations statewide have generally increased over the last 60 years, according to a new University of Wisconsin-Stevens Point analysis of state trout surveys.
"We see a general, overall increase in the catch per stream mile of trout, and in trout in all the size ranges examined, in fisheries surveys conducted since 1950," says Nancy Nate, Ph.D., the principal investigator and a scientist at the UW-Stevens Point Fisheries Analysis Center.
Nate and fellow researchers Andy Fayram and Joanna Griffin, fisheries analysts at the Wisconsin Department of Natural Resources, plumbed DNR databases for results from thousands of fish surveys the DNR conducted between 1950 and 2010 using electrofishing equipment. The equipment delivers an electric current to the water that stuns the fish so they can be collected, weighed and measured before being returned to the water. Catch per stream mile is used as an indicator of abundance in streams.
Fayram says it's the most comprehensive look ever at what's happening in Wisconsin's trout streams statewide. The DNR contracted with Nate to conduct the analysis to help provide information as part of its review of its trout program.
What Nate and her fellow researchers found was higher numbers per stream mile of trout statewide overall, and increased numbers per stream mile in each of the size ranges examined: brook trout over 7, 8 and 9 inches, and brown trout over 7, 9 and 12 inches.
Not as clear, however, are the reasons why trout numbers increased, including the role regulations played, one of the original questions she hoped to answer.
"At the very least we can say that trout populations have continued to improve under Wisconsin's current regulatory structure," Nate says.
Veteran state fish biologists say the factors fueling salmonids' success vary somewhat by region, but that changing land use and improved land management are factors. Habitat improvement work done by DNR and partners, anglers' embrace of catch-and-release fishing, and DNR's shift to stocking more trout spawned from wild fish also are factors, as are regulations, acquisition of sensitive lands along streams, and beaver control in northern Wisconsin.
Trout fishing regulations
Nate also was interested in determining, to the extent possible, the efficacy of different trout angling regulations on trout populations as Wisconsin reviews its trout program and readies for a public participation process to learn how trout anglers' fishing habits and preferences have changed over the past two decades.
Before the category system of regulation took effect in 1991, an angler could keep 10 trout over 6 inches from most streams. The system placed all trout streams in one of five categories (now reduced to four) and applied base regulations to each category. Among the "special regulation" streams, about 3 percent of Wisconsin trout water, there were 36 different regulation types that restricted gear, bag limits, seasons, and size limits in various combinations.
Nate found that this diversity of regulations and the lack of contrast to streams with no regulations to serve as controls made it hard to determine how a given regulation category performed compared to others. In general, however, she found that streams with a daily bag limit of three and an 8-inch minimum for brook trout had the highest total density and density of fish greater than 9 inches among the four regulation categories.
Conversely, streams that had one of the "special regulations" had high densities of total brown trout and of brown trout greater than 12 inches, though the densities were only statistically higher than densities in streams with a daily bag limit of 5 and a 7-inch minimum.
FOR MORE INFORMATION CONTACT: Nancy Nate, UWSP (715) 342-5338; Andy Fayram (608) 267-7654