Gill lice are a parasite of brook trout that have always lived in balance with the trout with. Now, increases in gill lice in waters were previously there was none have biologists' attention. / Wisconsin Department of Natural Resources
FOR MORE INFORMATION CONTACT:
Matt Mitro, 608-221-6366; Maureen Ferry, 608- 261-6450
Despite their small size, New Zealand mudsnails are very hardy and potentially very prolific, stirring concerns about potential impacts on food webs. / Wisconsin Department of Natural Resources
MADISON — With a potentially prolific invasive snail recently documented in Black Earth Creek, one of Wisconsin's premier trout waters, and a native parasite spreading among brook trout statewide, anglers can help keep Wisconsin fish and streams healthy by taking a few key prevention steps after fishing during the early catch-and-release trout season.
"Prevention steps work and everyone's vigilance matters," says Deborah Seiler, aquatic invasive species outreach coordinator for the Wisconsin Department of Natural Resources and UW-Extension.
The good news is you don't have to avoid fishing Black Earth Creek or any of the streams where gill lice have been reported," says Matt Mitro, a DNR trout researcher involved in efforts to stem the spread of gill lice and the snails. "As with any lake or river statewide, you're required to clean your gear and drain water from equipment after leaving and before entering another stream. We also recommend disinfecting that gear as well to reduce even more the risk of spreading New Zealand mud snails and other aquatic organisms."
Mitro and Seiler are part of a multi-partner group formed to respond to the discovery in Dane County's Black Earth Creek of the New Zealand mudsnail. The invasive species is present in the western United States and in the Great Lakes; the Black Earth Creek discovery marked the first documentation in inland Midwestern waters.
It's hard to predict how the snails will impact the stream, as in some western locations they have had minimal impact, or the snail populations have crashed after an initial boom, Seiler says. But in the worst case scenarios, mudsnails in some western U.S. waterbodies have been found growing at densities of up to 500,000 per square meter, changing native food webs and potentially decreasing the size and abundance of trout.
Trout Unlimited, River Alliance of Wisconsin, and other state, federal and county agencies are also partners. The response team will be monitoring other streams to look for mudsnails and conducting outreach to stream users, including anglers, researchers, and the construction industry. The River Alliance is seeking an early detection and response grant from DNR to try to contain the snail.
The same prevention steps for the mudsnail may help prevent the spread of gill lice and other aquatic organisms. Brook trout and gill lice have always lived together in Wisconsin streams but recently the balance appears to be tipping toward higher gill lice numbers in some streams. The parasite attaches to a brook trout's gills making it difficult for the fish to breathe and slowing normal growth and development. This increase in gill lice in some streams may be reducing trout numbers, Mitro says.
Statewide, 2013 efforts by anglers and DNR biologists to record the presence of gill lice, a native parasite of brook trout, reveals that gill lice are widely distributed across the state, except they appear to be absent in the Lake Superior basin, or at least in the samples of streams and trout inspected there, according to Mitro. "The prevalence and intensity of infection varies widely, with no geographic "hot spots," he says.
Taking steps to prevent the spread of the New Zealand Mud Snail and other aquatic organisms will just take a few extra minutes but can help keep trout populations and fishing strong, Mitro and Seiler say.
Before leaving a waterway:
- Inspect equipment and remove attached plants and animals
- Drain all water from equipment
- Scrub equipment with a stiff brush, including crevices, to remove adults
- Rinse equipment with tap water to remove juveniles
- Soak in 2 percent Virkon solution (2.7 ounces per gallon) for 20 minutes and
- Rinse clean away from surface waters.
- Change gear before entering another stream.
- Do not use felt soled boots
Anglers can report gill lice observations at the following webpage: http://www.wisconsintu.org/gilllice.
More news from the Wisconsin Department of Natural Resources.