A USDA Wildlife Services crew killed 70 cormorants on Lake Vermilion on May 29 as part of an effort to reduce the cormorant population on the lake, said Duane Williams, Department of Natural Resources large-lake specialist at Tower. The day before, DNR officials had counted 349 cormorant nests on Potato Island in the eastern basin of the lake. That total was down from 434 nests last year.
Each nest is assumed to represent one breeding pair of cormorants.
The birds where shot with shotguns. State and federal agencies had decided to take about 10 percent of the total number of nesting cormorants, Williams said.
After the culling, Wildlife Services crews oiled all of the eggs in the cormorant nests on the island with corn oil. Oiling the eggs prevents young from hatching successfully, but adult cormorants remain on the nests. If the eggs were destroyed, the adults likely would re-nest and lay new eggs, Williams said.
The cormorant population on Lake Vermilion, which has been increasing since 2004, is thought to be responsible for a low population of perch, an important forage fish. In 2004, cormorants had just 32 nests on Lake Vermilion, Williams said.
“We’ve had persistently low perch catches (in test nets) for a number of years,” Williams said. “We felt that (the cormorant population) was the most likely explanation.”