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Great Lakes Article:

Cormorants targeted for DNR study
Bird's fish-eating habits concern Green Bay anglers

By Jim Lee
Wisconsin Rapids Daily Tribune
Published June 20, 2004



Wisconsin anglers relish a meal of yellow perch, but so do cormorants and white pelicans.

As the perch population has declined in the waters of Green Bay, angler bag limits have been curtailed, but no such dietary restrictions apply to wildlife.

In an effort to satisfy angler concerns, the Department of Natural Resources has launched a $90,000 study of the dining habits of the two major fish-eating bird species on the bay.

"The reason the study is coming about is the U.S. Fish and Wildlife Service has given states the authority to manage cormorant populations," said Sumner Matteson, DNR avian ecologist.

"Commercial and recreational fishermen perceive cormorants as heavily preying on yellow perch, and they have asked what the state is doing about it.

"The limited data we have suggest perch are a small part of their diet, but we need this study to provide the best assessment of the situation."
Cormorants and pelicans are suspects because their numbers skyrocketed just about the time the perch population on Green Bay plummeted. Perch numbers declined 90 percent between 1988 and 2000.

Cormorants, a historic presence in Wisconsin, nearly disappeared from the state by the early 1960s, a victim of DDT, habitat loss and illegal human activity. Largely through DNR restoration efforts, the population has rebounded from a low of 66 nests in 1973 to a current level estimated at more than 11,000 breeding pairs, Matteson said.

"About 81 percent of the breeding takes place on four islands (Cat, Spider, Jack and Hat) in Green Bay," he said.

White pelicans have a historical presence in the state, but the first documented nesting occurred just 10 years ago, Matteson said.

In 2003, the DNR found 907 pelican nests, more than 400 in lower Green Bay.

Why did Wisconsin, previously shunned as a nesting site, suddenly become a pelican incubator?
"That's the $64 question," Matteson said. "No one really knows for sure."
Both cormorants and pelicans, which typically arrive in Wisconsin waters during April and depart by the end of November, feed heavily on fish. Cormorants reportedly consume about one pound of fish daily, with their favored targets in the 6- to 12-inch range.

Foraging habits differ. Cormorants are capable of diving fairly deep in search of prey, but white pelicans tend to feed in groups for the purpose of herding small fish in shallow water.

Matteson said previous studies found alewife, stickleback and other forage species predominated in the cormorant's diet. Since that time, alewife numbers in Green Bay have declined while yellow perch appear on the threshold of making a comeback.

Bill Horns, DNR Great Lakes fisheries specialist, said the department is in a good position to evaluate the impact of cormorant and pelican predation on the bay fishery, adding that a good yellow perch hatch in 2003 should produce fish of a size attractive to cormorants by this summer.

"The stars are in alignment for a good study," he said.

Results will be of interest to anglers on inland waters where cormorants have taken up residence in recent years. Matteson said flowages have become particularly attractive to cormorants, while Horicon Marsh harbors more than half the state's pelican nests.

The study is funded for two years, though Matteson says a third year is desirable to enhance scientific accuracy. Funding comes from a DNR settlement with paper companies for damage caused by past pollution on the Fox River and Green Bay.

Cormorants and white pelicans aren't the only perch predators recently restored to abundance on the bay. Walleye, spotted musky, salmon, trout, smallmouth bass, white bass, catfish and sheepshead are on hand in larger numbers than before the previous perch heyday.

Add to that mix the uncertain impact of undesirable exotic species, including zebra mussels, white perch, round goby, milfoil and other environmental factors, and it's a fair bet that trimming the cormorant population won't be the end-all solution to the bay's yellow perch woes.

The most favorable outcome would be to find the perch population has shrugged off this wave of outside factors and is rebounding on its own.

 

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