Killing Off Cormorants

  • Some people blame the double crested cormorant for fishing woes, but researchers say the bird might actually help some fish populations. (Photo by USFWS)

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 as Bob Allen reports, other researchers are not so sure killing cormorants will mean more perch, walleye and bass for anglers.

The MI DNRE says cormorant control works

A related TER story

More information from the USFWS


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. There are now roughly 60,000 of the large black duck-like birds in Michigan alone, but that’s put anglers in an uproar.

For the last decade they’ve been complaining that cormorants are a plague on popular fishing grounds.

Wildlife officials responded by reducing the number of cormorant nests in Michigan by 40% over the last six years, and they want to cut the population in half.

They do that by shooting birds each spring and spraying vegetable oil on their eggs to smother them. In one popular perch fishing area, they took cormorant numbers down by 90%.

Dave Fielder is the lead researcher in the Les Cheneaux Islands of northern Lake Huron for the Department of Natural Resources and Environment. He says he now sees the fishery there doing better and people catching more perch.

“You can’t go in and tweak it a bit and expect to measure. 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 not all researchers agree with Fielder’s findings.

Jim Diana is a professor of natural resources at the University of Michigan and director of the Sea Grant program in the state. He says many other factors, such as invasive species, contribute to fluctuating perch populations, and Diana 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 even any better fishery over time.

“And so it’s all a guess work in my mind. 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.”

Another place DNRE officials want to hit hard is the Beaver Island chain. They say a large number of cormorants there may be feasting on smallmouth bass.

Nancy Seefelt is a bird specialist at the Central Michigan University field station on the island. When she examines the stomach contents of dead cormorants she finds they are not eating bass. They’re primarily feeding on a small fish called the round goby. The goby is an invasive species that’s exploding in numbers in the Great Lakes. Gobies feed on the eggs of perch and bass. Seefelt says cormorants may actually be helping those game fish populations.

“I think that cormorant control should be based on science and the data that we have as opposed to politics. So the current, I guess, control that’s happening in the Beaver Archipelago is not something I’d say I support.”

DNRE managers argue that cormorant numbers are so high they can’t wait ten years for researchers to come up with more definitive answers, and this summer they expect federal approval to double the yearly kill in Michigan to 20,000 adult birds.

For The Environment Report, I’m Bob Allen.

By the way, the Great Lakes population of cormorants winters in the Gulf states. It’s not yet clear how the oil spill will affect them.

That’s the Environment Report. I’m Rebecca Williams.