Fisheries officials plan to kill part of the cormorant population on Lake Vermilion in northeastern Minnesota because its perch population has fallen and they worry that the decline could eventually harm the scenic lake's walleye numbers, the Department of Natural Resources said Monday.
Several years of surveys have shown depressed numbers of perch, the lake's primary forage fish for walleye. Don Pereira, the DNR's fisheries policy and research manager, said in a statement that they believe Vermilion's growing population of perch-eating birds is the reason.
The DNR's plan calls for culling 10 percent of Vermilion's adult cormorants and oiling the eggs of all nesting pairs, which prevents the eggs from hatching.
Double-crested cormorants established 32 nests on Vermillion's Potato Island in 2004. Last year, researchers counted 424 nests, up nearly 30 percent from 2011. Lower perch counts were first noticed in 2007, though the DNR said the reduced perch numbers haven't resulted in significantly lower walleye counts so far.
"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,'' Edie Evarts, the DNR's Tower area fisheries supervisor, said in the statement.
Evarts said the agency is applying what it has learned about cormorant impacts on fish populations over the past decade.
Wildlife managers killed thousands of cormorants from 2005-2009 on Leech Lake, where the birds were blamed for a drop in walleye numbers. DNR officials have credited those efforts for the resurgence of good fishing on Leech Lake, though some researchers have questioned whether cormorant control was the reason.
Cormorants are native to Minnesota. The statewide population is estimated at about 40,000 birds and has grown in recent decades since the elimination of the pesticide DDT.