Lake Vermilion is the latest Minnesota lake where double-crested cormorants will be controlled.
The Department of Natural Resources plans to reduce the cormorant population on the lake by culling 10 percent of the adult birds and oiling the eggs of all nesting pairs. Oiling prevents the eggs from hatching.
Cormorants eat yellow perch and potentially small walleyes. Several years of surveys show a consistently lower perch population in the lake's east bay. Perch are the lake's primary forage fish for walleyes.
"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."
Officials have been culling the cormorant population on Leech Lake for several years.
Double-crested cormorants established 32 nests on Vermilion's Potato Island in 2004. Lower perch counts were first noticed in 2007 and have remained depressed since. In 2012, 424 nests were counted, nearly a 30 percent increase from 2011. Reduced perch numbers have not resulted in significantly lower walleye counts in the 39,000-acre lake.
Not yet anyway. Edie Evarts, DNR Tower area fisheries supervisor, said the cormorant control is designed to reduce the possibility of lower walleye numbers in the future.
The control is being implemented under a depredation order administered by the U.S. Fish and Wildlife Service.
Cormorants are native to Minnesota. The statewide population is estimated at 40,000 birds. Like bald eagles and other fish-eating birds, their abundance has increased in recent decades because of 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, the DNR reports.