Michigan wildlife officials are pushing for more control of a fish eating water bird. They want to double the number of cormorants killed in Michigan each year, to about 20,000.
Cormorants nest in colonies on islands in the Upper Great Lakes and Canada, and they can gobble up a lot of fish.
But, some other researchers are not so sure killing more cormorants will mean more perch, walleye and bass for anglers.
A Native Anglers Didn't Miss
Thirty years ago, the double crested cormorant was a poster bird for toxic contaminants like DDT in the Great Lakes. Wildlife biologists used to take live birds with crossed bills and other deformities to public meetings to press for cleanup of the lakes.
Since then toxins have been reduced, and cormorant numbers have rebounded dramatically.
But that put anglers in an uproar about the large black duck-like birds. They charge cormorants are a plague on popular fishing grounds.
Eventually, federal wildlife officials allowed about 10,000 cormorants to be killed in Michigan each year.
Pete Butchko is the federal agent in charge of cormorant control in Michigan. He says he still hears cries to kill them all.
"Some people may want Michigan to be cormorant free," he says. "It's just not going to happen. Cormorants are native and have a place here."
But what that place is continues to come up for heated debate. In the last six years, wildlife officials cut the number of cormorant nests in Michigan by about a third. They did it largely by shooting the birds and spraying vegetable oil on their eggs, to smother them.
Killing Cormorants Help Fish
An area they hit hard was the Les Cheneaux Islands in northern Lake Huron. It's been a popular destination for perch anglers for decades.
Dave Fielder, the lead fisheries researcher for the Michigan DNRE in that area, says as they knocked down cormorant numbers by 90 percent, he could see the fishery improve. People began catching more perch.
"The Les Cheneaux Islands experience says at least in certain places there are real tangible benefits from cormorant control," he says.
Not So Fast
But not all researchers agree with Fielder's findings, including Jim Diana, a professor of natural resources at the University of Michigan and director of the Sea Grant program in the state.
Diana says many other factors such as invasive species and changing water levels have contributed to fluctuating perch populations throughout the Great Lakes.
But unlike those factors, he says, cormorants are highly visible.
"And as a result now cormorants are being targeted for removal, I think without any good evidence that it's going to have any effect," he says.
The DNRE wants to reduce cormorants overall in Michigan by half, and a place they want to focus on next is the Beaver Island chain. There, anglers and the DNRE say, cormorants may be feasting on a once thriving smallmouth bass population.
But Nancy Seefelt, a bird specialist at the Central Michigan University field station on the island, has examined the stomach contents of dead cormorants. She finds they aren't eating bass. They're primarily eating a small fish called round gobies, an invasive species that's exploding in numbers in the Great Lakes. They compete with perch and feed on their eggs and on the eggs of other fish such as bass.
Seefelt wonders if cormorants are doing more good than harm in the Beaver Islands.
"We don't really fully understand the roles of all the players in the system yet," she says. "We've been trying to tease it out, but it's very difficult to study a system that's partially terrestrial and partially aquatic."
So What Makes Sense?
State fisheries researcher Dave Fielder agrees the system is complex and there are a lot of factors that can't easily be controlled or measured. But, he argues, cormorants numbers are so high wildlife managers can't wait ten years for researchers to come up with definitive answers. And so, to him, it makes sense to take a big swipe at the birds.
"You can't go in and tweak it a bit and expect to measure," he says. "You've got to really punctuate the system in a big way so that you're sure you can measure a response. And that the response can be attributed back to that management action."
But Jim Diana with Sea Grant says the evidence just isn't there to show that if the cormorant population is cut in half there will be twice as good a fishery or any better fishery over time.
"It's all a guess work in my mind," he says. "And a guess work at the expense of a fair amount of management money to try to control them and also a cormorant population that many people would say has rights of its own."
The head of Wildlife Services says the federal agency spends roughly $100,000 dollars a year to control cormorants in Michigan. But the agency is going to need more than that to kill twice as many cormorants as they do now. This summer it's expected to approve an order to do just that.