New invader reaches Gile flowage
Written by Ironwood Daily Globe   
Friday, 09 December 2005 11:01

While an effort has been made over the past few years to educate users of the Gile Flowage about spiny water fleas, a new invasive species has entered the picture.

The Chinese mystery snail has been identified in the 3,400-acre flowage, Dr. Dean Premo said Wednesday evening in reviewing an environmental assessment he prepared for the towns of Pence and Carey. The study was funded with a Department of Natural Resources grant.

Premo said that while spiny water fleas eat native plants that are valuable to fish, it's not known what effect the snail might have on the flowage.

"We really don't know much about their impact," Premo said. "They probably came from aquarium owners."

The snails, which can be purchased in pet stores, keep the glass clean in aquariums.

Peg Sutherland, secretary the Friends of Gile Flowage (FOG), said the snails burrow in the sand and especially can be seen in the fall near the County C boat landing, on the east side.

"Walk along the shoreline, and all you hear is crunch, crunch, crunch," she said.

Chinese water snails are olive brown, from one to two inches long.

Tiny water fleas were found in the flowage in 2003, marking the first and only occurrence of the animal in a Wisconsin inland lake. They likely spread from nearby Lake Superior, since they have been in the Great Lakes since the 1980s.

Premo's report notes the water fleas have long, spiny tails that make them difficult for small fish to eat. "In fact, their sharp spines can pierce the lining of a fish's gut," he said.

The water fleas also eat other tiny fleas that are important food sources for fish, said Premo, of White Water Associates, headquartered in Amasa, Mich.,

Through an educational campaign spearheaded by FOG, boaters are being encouraged to thoroughly empty bilge water and clean their boats before entering or leaving the flowage.

This fall, the DNR stocked bluegills obtained from another Iron County lake into the Gile, hoping they will put a dent in the spiny flea population.

DNR biologist Craig Roesler identified two ways to cut down on the flea population. The stocking of bluegills was selected.

The alternative would have been to draw down the flowage to flush out the invaders, but that would also have an adverse impact on gamefish populations, Premo said.

Premo noted the water fleas were present in one Minnesota lake, but disappeared. "That could happen here, too," he said.

The flowage is noted for its walleye and musky fishing, although walleye population densities are thought to be well under the carrying capacity, which some fishermen attribute to the introduction of smallmouth bass. Panfish show good growth, but aren't abundant and that's why the bluegills were stocked.

Premo offered some insights as to how plant life in the flowage affects fish species. He said 11 of 24 plants included in his study are considered "fisheries valuable."

Shallow areas of a body of water are the most productive for plants, which grow along the 26 miles of the Gile shoreline.

Xcel Energy draws down the Gile twice annually, which has a huge effect on plants. The summer drawdown, which begins around May 1, averages six feet; the winter drawdown is up to eight feet.

"Aquatic plants can't establish well in fluctuating water levels," Premo said. He described flowage plants as an underwater forest. "We call them weeds. They don't get much respect, but are very important," he said.

Because the flowage water is so dark, the maximum depth at which plants grow is only about two feet, said Premo, who was assisted in his study by several FOG members.

There's good news in the study regarding water quality. Premo said that while he expected to find many types of heavy metals because of past mining in the Montreal area, most metals were below what's called the "threshold effect concentration (TEC)."

Mercury levels were slightly elevated at 2.03 parts per trillion and cadmium was slightly above the TEC.

"I was bracing myself to see more heavy metals," he said.

The DNR has issued mercury advisories for the flowage for the past several years, advising pregnant women and young children to avoid eating larger walleyes.

Premo advises area residents "to throw back those 24-inch walleyes and eat the 16-inchers," which contain far less mercury.

Sampling mercury is so sensitive that breathing on a test tube can affect the results if the person taking the sample has a dental filling with mercury, Premo noted.

Unlike many acidic northern Wisconsin lakes, the Gile water was relatively "soft," with pH levels measured at from 7.4 to 8.1. Acidic lakes measure from 4.5 to 5.

"It's actually a very fertile lake," Premo said.

Cathy Techtmann, of Pence, president of FOG, noted the study is important because there had been little previous information on the flowage at a time when Pence and Carey are developing comprehensive (Smart Growth) plans.

"It's a unique body of water and very special," she said.

She noted funding has been received to place large signs at four boat landings, welcoming people to the flowage and identifying exotic species. It's part of the educational effort to stop the spread of spiny fleas and Chinese mystery snails.

 
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