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Serving Northern St. Louis County, Minnesota

DNR approves cormorant control on Lake Vermilion

DNR to cull ten percent of the population and oil eggs to slow breeding

Marshall Helmberger
Posted 4/26/13

LAKE VERMILION—The Department of Natural Resources will take steps to control Lake Vermilion’s burgeoning cormorant population this summer. The decision, announced this week, comes after calls by …

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DNR approves cormorant control on Lake Vermilion

DNR to cull ten percent of the population and oil eggs to slow breeding

Posted

LAKE VERMILION—The Department of Natural Resources will take steps to control Lake Vermilion’s burgeoning cormorant population this summer. The decision, announced this week, comes after calls by a number of resort owners on the lake to take action before the lake’s fishery is damaged.

“I think it’s a good idea,” said Dave Lamwers, owner and operator of Forest Lane Resort. “I’m glad to see the DNR taking action before the fishery is in the hopper,” he said.

The double-crested cormorant population has grown across the Midwest in recent years, as the species has recovered from very low numbers in the 1960s and 70s. Like many predatory birds in the aquatic food chain, cormorants were affected by the widespread use of DDT, an insecticide that weakened the eggshells of many bird species, such as bald eagles, pelicans, and loons.

The phaseout of DDT and federal protection against indiscriminate shooting allowed cormorant populations to recover and the species has been blamed in recent years for harming fish populations in a number of well-known Minnesota lakes, including Leech Lake.

The U.S. Fish and Wildlife Service has allowed the DNR and other cooperators in Minnesota to cull a certain number of the birds under a depredation order approved in 2003. DNR officials and others have culled thousands of the birds on Leech Lake in recent years, although far fewer are likely to be taken on Lake Vermilion, at least for the foreseeable future.

Under the quota allotted to Lake Vermilion, the DNR could kill as much as 10 percent of the adult cormorant population this year. They will also spread vegetable oil on cormorant eggs they find, which suffocates the young developing birds, without prompting the adults to lay new eggs. Together, this approach controls existing numbers of birds, eliminates new production and reduces fish consumption that would have occurred from feeding and raising young birds. This initial control strategy will be monitored for effectiveness by measuring perch abundance in annual netting surveys and counting the number of nesting pairs of cormorants each year.

Most of the control actions will center on Big Bay’s Potato Island, the primary nesting site on Lake Vermilion.

DNR officials say recent fish surveys, which show a decline in perch numbers in the lake’s eastern basin, justify the control measures. “We believe cormorant predation is the likely cause of fewer perch being caught in survey nets,” said Don Pereira, DNR fisheries policy and research manager. “This conclusion is based on the ‘weight of evidence’ that came from analyzing fish population data.”  Reduced perch numbers have not resulted in significantly lower walleye counts in the 39,000-acre lake. 

Edie Evarts, DNR Tower area fisheries supervisor, said the upcoming cormorant control is designed to reduce the possibility of lower walleye numbers in the future. “Limited control measures are a reasonable approach to insure cormorant impacts to the perch population do not result in a declining walleye population as well,” Evarts said. The agency is applying what it has learned about cormorant impacts on fish populations over the past decade, she said.

The DNR had documented a similar decline in the perch population on Leech Lake in the years just prior to the collapse of the lake’s walleye population in the mid-2000s.

Lake Vermilion resort owners have been urging the DNR to act on Lake Vermilion before conditions reach that point, and it now appears that DNR officials took those arguments to heart.

Cormorants established 32 nests on Potato Island in 2004. The colony has steadily increased. In 2012, counters tallied 424 nests, nearly a 30 percent increase from 2011. Lower perch counts were first noticed in 2007 and have remained depressed ever since.

Future control recommendations will be adjusted by the response of perch abundance to the control implemented. The control is being implemented under a public resource depredation order administered by the U.S. Fish and Wildlife Service. 

Cormorants are native to Minnesota. The statewide population is estimated at about 40,000 birds. Like bald eagles and other fishing-eating birds, their abundance has increased in recent decades due to the elimination of the pesticide DDT, which had a negative impact on reproduction, and protection under the Migratory Bird Treaty Act. In most places where colonies exist, popular fisheries have not been affected.

Cormorants, Lake Vermilion