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Serving Northern St. Louis County, Minnesota

Cormorant control completed on Vermilion

Ten percent of adults killed, young of the year sprayed to prevent hatching

Marshall Helmberger
Posted 6/12/13

LAKE VERMILION—Lake Vermilion’s cormorant population is down this year, due in part to Mother Nature, as well as the intervention of federal wildlife officials who undertook control measures on …

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Cormorant control completed on Vermilion

Ten percent of adults killed, young of the year sprayed to prevent hatching

Posted

LAKE VERMILION—Lake Vermilion’s cormorant population is down this year, due in part to Mother Nature, as well as the intervention of federal wildlife officials who undertook control measures on the fish-eating birds on May 29.

The Department of Natural Resources requested the control measure earlier this year out of concern that Vermilion’s growing cormorant population could stress the lake’s fishery. To date, Vermilion’s walleye population remains very strong, but DNR officials have documented weak perch numbers for the past several years, which could be an indicator of problems ahead for other fish species. The DNR and the Lake Vermilion Sportsmen’s Club have documented a ten-fold increase in cormorant numbers in the past eight years, and the trend has worried the lake’s resort owners and fishing guides, who say they don’t want Vermilion to experience the kind of walleye population crash seen on Leech Lake when cormorant numbers spiked there about ten years ago.

The DNR implemented control measures on Leech Lake in the mid-2000s, and the walleye population has since rebounded, but the recovery of the local fishing industry has been a slow and painful one, according to local resort owners.

While Vermilion’s cormorant population had been skyrocketing, the nest count conducted May 28 on Vermilion’s Potato Island, found 349 nests, about a 25 percent drop from 2012.

DNR large lake specialist Duane Williams said it isn’t clear if the decline was due to the late spring or other factors. “These colonies do tend to fluctuate some,” he said.

The DNR had previously authorized killing ten percent of the adult cormorant population and 100 percent of the young of the year. Given this year’s nest count, which translates into approximately 700 adult cormorants, the DNR approved the taking of 70 birds, which federal sharpshooters from the Animal Control office in Grand Rapids completed on May 29. According to Animal Control spokesperson Carol Bannerman, the birds were taken with suppressed .22 caliber rifles with special, subsonic ammunition which operates nearly silently. Bannerman said the use of silencers and special ammunition reduces stress on non-targeted birds and also limits nuisance noise for anglers or others in the area.

After shooting their quota of adults, the control specialists sprayed all of the eggs on Potato Island with corn oil, marking the nests as they went. The team will return in the next week or two to check for any new nests. The sprayed eggs won’t hatch, but the remaining adult cormorants will continue to incubate them, reducing the likelihood of re-nesting.

While cormorants are a protected species, the DNR does have authority to control the population in certain circumstances under a depredation order issued more than a decade ago by the U.S. Fish and Wildlife Service.

Future control measures possible

This was the first year for cormorant control measures on Lake Vermilion, but it may not be the last. According to Williams, the DNR is using a population model developed on Leech Lake to determine whether control measures are needed in the future. Each spring, the DNR will conduct a count to determine if additional control measures are justified. The model uses “foraging days,” which is determined by the number of days that cormorants reside and forage on the lake times the number of birds. That model sets the trigger point at 2.8 foraging days per acre, a formula that would allow just over 600 cormorants, including fledged young of the year, on the lake during a six-month open water season.