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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

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June 2005

Researching the threat

Issues, results and future challenges

Natasha Kassulke

Rusty crayfish and rainbow smelt | Spiny water flea
Wetlands | Sea lamprey success story

Jeff Bode, DNR's lakes and wetlands section chief, knows that some people are frustrated that resource managers don't have better tools in place to stem the spread of exotics.


"Sometimes problems evolve faster than the solutions," Bode says. "Dealing with exotic species is much like the medical field in that we might not have a cure yet, but with continued research there is hope."

Tom Hrabik, a fisheries ecologist and native of north central Wisconsin, agrees. Since he was a child, he has been interested in how the presence of rainbow smelt (Osmerus mordax) has affected walleye and other native fish in northern Wisconsin. He saw firsthand the negative effects that exotics can have on a fishery. But his research into exotics has expanded since he studied lakes in Northern Wisconsin. Today, he is an assistant biology professor at the University of Minnesota-Duluth and continues to study rainbow smelt in Lake Superior. However, he is also involved in studies of round gobies (Neogobius melanostomus) and ruffe (Gymnocephalus cernuus) in the St. Louis River.

"There is a growing need to examine the effects of exotic species and many students are now choosing to focus on exotics as part of their graduate research," Hrabik says.

In fact, the University of Wisconsin is leading much of the research in Wisconsin on how to control the spread of aquatic exotics and predict the likelihood of an invasion.

Big Bay State Park is one of many special areas researchers hope to protect from invasives. © Robert Queen
Big Bay State Park is one of many special areas researchers hope to protect from invasives.

© Robert Queen

John Magnuson, director emeritus of the UW-Madison Center for Limnology, has based a career on long-term lake ecosystem research including the influence of invasives and climate change on biodiversity.

"Climate change will increase the range of exotic organisms in Wisconsin, especially as it relates to fishes," Magnuson predicts. He points to research published by the Intergovernmental Panel on Climate Change and the Union of Concerned Scientists that supports his statement.

"By the end of the century we would expect animals that live in Northern Illinois to be able to thrive in northern Wisconsin due to warmer temperatures," he says. Warmer winters may allow invasives to become established and even dominate some aquatic communities.

While climate change is a long-term issue, several other researchers are building on Magnuson's work with exotics to find more immediate answers for how to stop the spread of invasives that are already here.

Rusty crayfish and rainbow smelt

Jake Vander Zanden, an aquatic ecologist and University of Wisconsin professor of limnology, is interested in predicting which lakes are vulnerable to an invasion, thus being able to concentrate prevention efforts on those lakes.

"With approximately 15,000 lakes in Wisconsin, how do we focus our efforts most effectively?" he asks.

Vander Zanden asks three questions when determining a lake's vulnerability to invasion: can they get there, can they live there and can they impact the system? He found that the answers to these questions depend on the invader. His studies examine rusty crayfish (Orconectes rusticus) and rainbow smelt invasions in Wisconsin lakes.

"The rusty crayfish cause a decline in abundance of the native crayfish and clear-cut the weed beds," says Tim Kratz, director at Trout Lake research station in Vilas County. "Rainbow smelt have been linked to the local extirpation of yellow perch and ciscowet."

Kratz closely follows the research of Vander Zanden and others on Crystal and Sparkling lakes.

"There was cause for concern here," Kratz says. "First, we were trying to avoid transporting smelt and crayfish into the lake, but once they were here, we were asking what we could do about them?"

Ideas included stocking a predator. Walleye were introduced to prey on the rainbow smelt and bass to prey on the crayfish. Fishing regulations were adjusted to protect the predators.

At Sparkling Lake, Vander Zanden and others also trapped and manually removed rusty crayfish – about 70,000 crayfish over four years. The community held crayfish boils to "dispose" of the crayfish and some were donated as animal food.

Brian Roth, a UW-Madison graduate student, explains that the trapping was very labor intensive but effective in this case.

"We've found that in smaller lakes, removal by trapping is effective for rusty crayfish and that walleye are very effective smelt removers," Roth says, "but some lakes are just too big to take that approach."

There is evidence, though, that the project is working here. Aquatic plants are returning, providing critical habitat for fish and stabilizing sediments on the lake bottom.

"There are a lot of vulnerable systems in Wisconsin and we've done our best to see whether or not we can remove an invader once it is established and found that is very difficult," says Jeff Maxted, a UW Limnology Center research specialist. He says prevention is still the best line of defense. "As the world becomes smaller through international trade, animals and plants are moving more easily."

Spiny water flea

Pieter Johnson, another Limnology Center researcher, knew that the spiny water flea (Bythotrephes cederstroemi) has existed in the Great Lakes since the early 1990s. But it wasn't until 2003 that he discovered that it had moved into an inland Wisconsin lake. During a 64-lake survey, Johnson found the invader in the Gile Flowage, an impoundment in Iron County.

"Spiny water fleas are nasty; they eat the smaller forms of zooplankton that fish depend on and they are tough for fish to eat because their barbed terminal spines are sharp enough to puncture the lining of the fish stomach," Johnson says. "They can knock out a food supply and are potentially fatal to fish."

Johnson says it isn't known how long spiny water fleas have been in the Gile Flowage. The spiny water flea is a large (about inch long) freshwater zooplankton native to northern Europe and the Caspian Sea. It likely arrived in North America in ballast water.

In an effort to prevent spiny water fleas from spreading to other Wisconsin lakes, Johnson is working with the Department of Natural Resources to educate boaters that these fleas can be transported in live wells and bilge water and that the eggs can become attached to fishing tackle, anchor lines and mud on boats and anchors.

Informational fliers advising lake users of the potential spread of spiny water fleas have been posted at each of Gile Flowage's boat landings and in local bait and boating stores.


Joy Zedler, a professor in the University of Wisconsin Botany Department and the Aldo Leopold Professor of Restoration Ecology for the University of Wisconsin Arboretum, moved to Wisconsin from California in 1998 and quickly got to work on what she found to be the biggest threat to Wisconsin wetlands.

"I realized that the biggest problem in Wisconsin wetlands is invasive species," Zedler says.

As a restoration ecologist, her interest is in replacing invasives with natives. Several of her students have led projects that rely on field surveys, historical aerial photos, experimentation, restoration and replanting, and more. Collectively, these studies aim to understand how and why plant diversity is declining in wetlands, and how to develop approaches to restore natives and weed out the exotics.

Zedler's students are working within the UW-Madison Arboretum, throughout Wisconsin and across the Upper Midwest region. One project is helping to explain why reed canary grass (Phalaris arundinacea) and hybrid cattails, two of the most common invasive plants in Wisconsin wetlands, are increasingly dominant in wetlands that surround development. As development increases, surrounding wetlands tend to experience increased stormwater runoff and with that, more sediment and nutrients.

Another one of Zedler's students studies sedge meadows in Wisconsin that are dominated by tussock sedge. She is learning how increasing surface area and creating microhabitats affects plant distribution within sedge meadows. She has set up an experiment to test the usefulness of creating artificial bumps in sedge meadows to increase species diversity and coax back native species.

Sea lamprey success story

For Bill Horns, DNR's Great Lakes fisheries specialist, research and experimentation have played an important role in controlling sea lampreys (Petromyzon marinus), one of the most infamous invaders to the Great Lakes.

Sea lampreys are native to the Atlantic Ocean, resemble eels and feed on large fish. They came to the Great Lakes in the early 20th Century through shipping canals and today are found in all the Great Lakes.

Lampreys are enormously destructive. They attach to fish with a sucking disk and sharp teeth, and then feed on body fluids, often scarring and killing host fish. During its life as a parasite, each sea lamprey can kill 40 or more pounds of fish. Sea lampreys have had a serious negative impact on the Great Lakes fishery. Before sea lampreys entered the Great Lakes, about 15 million pounds of lake trout were harvested in lakes Huron and Superior annually. By the early 1960s, the catch was only 300,000 pounds.

The Great Lakes Fishery Commission was formed in 1955, primarily to control sea lampreys and support research in that area. The commission, with Fisheries and Oceans Canada and the U.S. Fish and Wildlife Service acting as agents, has coordinated and funded sea lamprey control on the Great Lakes for more than 40 years. Individual states and the U.S. Army Corps of Engineers have provided support for some control projects. For example, Wisconsin contributed to the construction of the sea lamprey barrier now on the Iron River. Research institutions throughout the Great Lakes basin conduct critical sea lamprey research.

Today, sea lamprey controls include barriers, mechanical trapping, and the release of sterile male sea lampreys, which compete with normal males for mates but produce no offspring. As sea lampreys became sufficiently controlled, lakes were stocked with chinook salmon and coho salmon, which control alewives, while also providing a recreational fishery.

"Overall," Horns says, "the sea lamprey control program has been tremendously successful." Ongoing control efforts have resulted in a 90 percent reduction of sea lamprey populations in most areas.

Natasha Kassulke is associate editor of Wisconsin Natural Resources magazine.