Evidence Shows Cormorant Control in Northern Lake Huron Is Working
May 14, 2009
To many Michigan anglers, double-crested cormorants -- those long-necked diving birds that have been evident in high numbers on Michigan's Great Lakes waters in recent years -- have no redeeming qualities.
They have been pointed at
as a primary cause of past declining sports fisheries, past and present, most notably the yellow perch fishery in northern Lake Huron and the smallmouth bass fishery around Lake Michigan's Beaver Island. And although cormorants are merely a part of a dramatically changing food web, there has been enough evidence of their role in the drama that the U.S. Fish and Wildlife Service has green-lighted some population-management efforts.
Those efforts include killing some adult birds and oiling eggs on the nest, for instance, so the young don't hatch. And while the number of cormorant nests at the Les Cheneaux Islands has been significantly reduced since the efforts began in 2004, one question remains: Does it work?
Based on the evidence collected so far, the answer appears to be, yes.
Cormorant control efforts began at the Les Cheneaux Islands because it offered an excellent test case. The birds' colonies were on the small uninhabited islands in northern Lake Huron, which offered an opportunity to target the nesting birds. Wildlife Services personnel from the U.S. Department of Agriculture used lethal measures, as well as preventative methods, to control cormorants.
The cormorant population was reduced by 15 percent the first year and by more in subsequent years. What nobody really knew, however, was whether the reduction would prove temporary. Today, there are around 500 nests in the area, down from a peak of 5,500, showing that it was possible to reduce the cormorant population.
But a second question remained: Did it matter to fish populations?
"We did see the emergence of some very strong yellow perch year-classes," said Dave Fielder, a Department of Natural Resources fisheries research biologist who is studying the issue. "Some of it may have been environmental, but these year-classes persisted; they lived longer and they recruited into the fishery, something that didn't occur when cormorant numbers were higher.
"The Les Cheneaux Islands is our best-studied control effort and, for the most part, it's been a great success. So, basically, yes, cormorant control has worked there."
The success of the pilot project has caused folks to call for more effort and more widespread control of the birds, which have been documented in Michigan since the late 1800s, but whose populations expanded beyond historical proportions in recent years.
Fact is, in the 1960s and '70s, cormorant populations plummeted because of the effects of pesticides (notably DDT) on their reproduction. Cormorant numbers sank so low the birds were added to the state's Endangered and Threatened Species List. But after DDT was banned, the birds recovered to the point they were removed from the list by the mid-1980s.
"We've got more cormorants now than were ever seen," said Karen Cleveland, the all-bird biologist in the DNR's Wildlife Division. "It's not so much that we accomplished a dramatic reduction as we stopped their increase. The actions that have been taken forestalled an increase in their numbers."
Even that success, however, has anglers at other places, who believe they are suffering at the wings of cormorants to call for a more widespread effort.
But fisheries biologists are unsure whether it will work. Different lakes have different food webs; will what seemed to work to improve perch populations in northern Lake Huron do the same thing for smallmouth bass populations around the islands in Lake Michigan?
"Knowing where and when to apply control is another question," Fielder said. "Based on our success at the Les Cheneaux Islands, I believe the Beaver Island Archipelago could be a good candidate for this kind of experiment in cormorant control."
On some inland lakes, where cormorant harassment programs are in effect, there's anecdotal evidence that it's having a positive impact. U.S. Department of Agriculture Wildlife Services personnel are harassing cormorants with noise-making devices, cracker shells and occasionally live ammo, to see what happens.
"At Brevort Lake, just west of the Mackinac Bridge, we have some pretty good information on the recovery of walleye since the harassment has begun," said Steve Scott, the fisheries biologist for the eastern Upper Peninsula. "It appears to be working very well. And we have anecdotal information that it's having positive effects on other inland lakes, but we don't have the data to document it yet. Anglers say the fisheries on Big Manistique Lake have recovered, but we haven't finished the surveys. We're conducting studies, but we don't have all the information we need."
Nonetheless, the DNR -- which does not kill the birds or oil their eggs, but makes recommendations on where to attempt control efforts to the agencies and tribes that are doing the work -- is planning to ramp up cormorant control efforts. Last year, about 8,000 cormorants were killed. This year, that number could hit 10,000, Cleveland said. "We're basically looking at increasing activity at existing locations," she said.
In addition, Michigan is seeking an opportunity to increase the number of cormorants that can be killed from its current ceiling of 10,500 a year (according to the federal permit) and is beginning to work with the Mississippi Flyway Council on developing a regional management strategy. Cormorants are highly mobile and localized management plans might just move the problem elsewhere.
"Demonstrating the effects of population control is complicated because of the constant change in the food web," Scott said. "It's difficult to tease out the true effects of cormorants when there are so many other variables out there."