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|Fair or foul? - Cormorants may be threat to fishery|
|Written by The Journal Times|
|Saturday, 29 January 2005 06:41|
Flying low, in a straight line or ragged-V formation, large dark birds fly past the rocks of Christopher Columbus Causeway in Racine, feathers rustling as they settle on the water.
Swimming with bodies submerged, head and neck above water, they dive beneath the waves to catch fish.
Not to be confused with geese or loons, the birds are double-crested cormorants, called crow-ducks by European settlers and Phalacrocorax auritus by scientists.
Ask an angler in many Great Lakes communities, and you'll likely get a decidedly different name for the fish eaters, many of which are not printable.?
From Lake Erie to Lake Superior, the big birds have come back in such a big way that some claim they are eating their way through fish stocks, leading to testy public hearings and calls to reduce cormorant numbers.
Wisconsin is now taking center stage in the cormorant controversy. A state-funded study to determine if the resurgence of cormorants is contributing to the decline of yellow perch in Green Bay is at its midway point, with early results showing that the birds eat fish, a lot of fish.
And if perch are around, they'll definitely eat those.
The two-year study, conducted by University of Wisconsin researchers and mostly funded by the Department of Natural Resources, is looking at cormorant predation patterns on fish in Green Bay.
Researchers examined the stomach contents of 436 birds in 2004 that revealed that of the 4,712 fish counted, 1,743 were yellow perch. That number was higher than for any other fish species counted, but yellow perch ranked second by weight as a food source, at 17 percent, behind white suckers, which comprised 40 percent.
One cormorant had 80 fish in its stomach. Another had eaten a 22-inch walleye.
The average cormorant contained 11 fish, including such species as gizzard shad, spottail shiner, round goby and alewife.
Is there a connection? The study will now focus on whether the number of perch the birds eat is statistically significant, says Sarah Meadows, a UW graduate researcher and the study's principal investigator.
"I'd be reluctant to draw any conclusions before the model has factored in cormorants as a source of yellow perch mortality, so we can have an accurate picture of the effect they're having on the perch populations in Green Bay," Meadows says. She hopes to have an answer to the significance question after data have been analyzed from the 2005 field season.
The DNR contracted with Meadows and Scott Craven, a UW wildlife ecology professor, to examine the food habits of the cormorants nesting in Green Bay, where more than 80 percent of Wisconsin's breeding population occurs.
The study was prompted by concerns among commercial fishermen and recreational anglers that cormorants prey on yellow perch, which may be causing or contributing to a 90 percent drop in yellow perch populations between 1988 and 2000. Declining yellow perch populations spurred the DNR to reduce sport bag and commercial harvest limits for yellow perch, at the same time populations of the federally protected bird rebounded in Wisconsin and elsewhere.
A quarter-century after cormorants were added to the state endangered species list, populations of the bird are at historic highs. There are more than 1 million cormorants in the United States and Canada, and more than 11,000 breeding pairs in Wisconsin.
Of this there is no doubt - cormorants can alter their ecosystems, so much so that the big birds were the subject of a 2003 federal environmental impact statement. The EIS recommended control measures, including oiling eggs and killing adults, in certain circumstances.
Visitors to Racine In recent years, they have become increasingly familiar sights along Racine's Lake Michigan shore. Although some cormorants can be seen in local waters from April to November, most are seen as they migrate through in spring and fall.
Cormorants have not been listed as a significant factor in the decline of perch in the Racine County waters of Lake Michigan, where researchers believe the problem lies in the early life history of the perch, most likely due to a lack of food.
But in Green Bay, where most of the state's 11,000 breeding pairs live and raise offspring, cormorants could have a significant impact on the perch population.
"Cormorants have no natural predators so the population has exploded since the DDT ban and that's having devastating effects on the natural system," said Dan Thomas, president of the Great Lakes Sport Fishing Council. "All cormorants eat is fish and they are voracious feeders. But they also crowd out desirable water birds from nesting sites and destroy natural vegetation wherever they roost."
The big birds have led some to unlawful action. In 1998, 10 New York state residents were given fines and home confinement sentences for the killing of more than 850 cormorants on Little Galloo Island in Lake Ontario.
Since then, the EIS has given states the ability to kill cormorants if deemed necessary.
"If you go to areas of Green Bay like Marinette, it's really evident as a problem," said Craig Bender, an avid angler and president of Salmon Unlimited of Racine, Inc. "Whatever is in their path, they're going to gobble it."
According to data derived from the DNR's creel survey, the estimated harvest of yellow perch by sport anglers in Green Bay was 67,543 fish in 2003, the last year for which data are available. The estimated sport catch of yellow perch for the same period in the Wisconsin waters of Lake Michigan, including Racine County, was 88,788 fish.
So, if there are 11,000 breeding pairs of cormorants in Wisconsin, and a single cormorant was found in the UW study to have 80 fish in its belly on a single day, it's easy to see why sport and commercial fishers are concerned about the impact the birds are having on the resource.
Expert divers, foragers Cormorants are expert divers, adapted naturally to forage under water for fish. Fully-webbed feet propel slim, streamlined bodies on dives usually from 8 to 20 feet, but greater depths are possible. Feathers absorb moisture, helping cormorants to stay under water for about 30 seconds. After foraging, cormorants often dry their feathers by perching in a distinctive wing-spreading posture.
The Great Lakes population of double-crested cormorants was devastated during the 1960s, primarily by the effects of chemical contamination, especially DDT. Because they are fish-eating birds at the top of the food chain and long-lived (up to 20 years), adults accumulated pesticides and other toxins from the bodies of their prey.
In the early 1970s, the Great Lakes population had plummeted, with few birds remaining or breeding successfully. In Wisconsin, the species was placed on the list of threatened and endangered wildlife. Nesting platforms were erected to aid their recovery.
Today, the Great Lakes population of double-crested cormorants is at historic highs. Pollution control has lowered concentrations of toxic contaminants in their food supply, food is ample throughout their winter and summer ranges, and they are protected by federal and state laws.
The UW researchers' work in Green Bay focuses on cormorants in an area running from the mouth of the Fox River at Green Bay northwest to Peshtigo Point and northeast to Sturgeon Bay, and includes a cormorant breeding colony at Cat Island.
After getting approval from the U.S. Fish and Wildlife Service, employees of the USDA's Wildlife Services program shot 436 cormorants between mid-May and mid-September. Meadows noted that the colony size increased in 2004 despite those losses; it contained about 2,000 breeding pairs at the end of summer.
Meadows also saw a seasonal change in forage species. Perch numbers in the cormorants' stomachs peaked in mid-June, then dropped off as the perch moved from shallow to deeper water. By mid-July, other species were much more common in the birds' stomachs. She also noted seasonal peaks in numbers of gizzard shad and round gobies, an invasive species.
Researchers will now try to determine whether cormorants eat enough perch to prevent the robust numbers of young fish hatched in 2003 and 2004 from reaching a fishable size. To learn the answer, Meadows and Craven will plug their data into a computer model that U.S. Fish & Wildlife Service scientist John Netto developed, drawing on yellow perch data that DNR fisheries biologists Brian Belonger and Justine Hasz had collected over the last 25 years.
"The timing of this study is really fortunate," said Bill Horns, a DNR Great Lakes fisheries specialist. "We had the money set aside, excellent scientists available with an interest in this work, a strong year class of yellow perch coming through, and a well developed model of the yellow perch population."
Money for yellow perch work was earmarked from settlements reached with paper companies for damage caused to natural resources from historic discharges containing PCBs.
Craven conducted research in the early 1980s into the eating habits of cormorants nesting on the Apostle Islands, and Meadows has studied the food habitats of different kind of cormorant in New Zealand.
Horns says that if the study demonstrates that cormorants are a problem for perch and the control measures would help, the agency would probably turn to USDA's Wildlife Services for help with control under a Public Resources Depredation Order issued in 2003 by the Fish and Wildlife Service.?
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