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Killing more carp: can this destroyer of waterfowl habitat be eradicated?

MALHEUR NATIONAL WILDLIFE refuge in Oregon was once a thriving marsh that attracted ducks by the tens of thousands. It's now an ecological desert of open, murky water that supports little aquatic life. Except carp. Less than 10 percent of the refuge's suitable wetland habitat remains and waterfowl production on the refuge is down even more. Over the last 70 years, managers have tried to remove the troublesome intruder. As many as 7.2 million pounds of common carp have devastated the refuge's three lakes.

"I'm a hard core duck hunter and I wouldn't hunt here," says refuge deputy project leader Jeff Mackay. "We have very few birds in the winter. On a scale of one to 10, I'd say the carp impact has been a 10. The entire ecology of the lakes has been destroyed."

Common carp inhabit 49 states and leave an equally dramatic trail of destruction in shallow water everywhere. A study conducted on two Illinois lakes found that carp reduced aquatic vegetation by nearly 90 percent and the number of waterfowl that visited Hennepin and Hopper lakes showed an equal decline. Minnesota DNR waterfowl staff specialist Steve Cordts says hundreds of lakes have a significant carp problem in his state. Many of them no longer attract ducks. Or duck hunters.

Non-native, highly adaptable and tolerant of poor water quality, a single common carp can lay a million eggs at a time. They were brought to the U.S. around 1850 from Europe and Asia as a high-quality, farmable food source and a perfect substitute for dwindling populations of native fish. Not surprisingly, carp made their way into waters all over the country, but wild carp had a decidedly different flavor than farm-raised carp and many of the native fish species. Nobody ate them. As they spread to more waters, sportsmen looked upon them with disdain, not only because they were a poor food source, but for what they were doing to the waters they inhabited. The fish root up the bottom in search of invertebrates and vegetation, stirring up sediment as they go. That sediment blocks sunlight, a necessary ingredient for submerged aquatic vegetation.

As the grass disappears, so do the ducks that feed on it and the bugs that live in it. It doesn't take a scientist to see that, but plenty of them have examined the impact of carp on waterfowl, including Dr. Przemek Bajer, a research assistant professor at the University of Minnesota. He led the study that followed the return of carp to Hennepin and Hopper lakes after an eradication effort failed. The lakes were drawn down and then treated with rotenone, a non-selective piscicide (fish poison). A barrier was also erected between the lakes and the Illinois River.

"Water clarity improved, grass returned and lots of ducks returned. Then the carp somehow got back into the lake and the water quality declined, the aquatic vegetation disappeared and so did the ducks," he recalls.

It's a pattern that's been repeated wherever carp removal efforts have been attempted and failed. The carp are removed or reduced, grass coverage spikes, ducks flock to the grass, carp return and everything spirals downward.

"It's shocking how well they can move from one system to another. They'll even swim through drain tiles buried underground to get from one lake to another," says Cordts. "Many of our lakes are connected by sloughs or ditches during periods of high water, so eradicating them from one lake is often only temporary. It takes between just five and 10 years for carp to rebuild their numbers enough to have a detrimental impact."

Despite ongoing control efforts dating back to the 1950s, carp keep rebounding on Malheur. Their numbers are down due to a lengthy drought, but Mackay says abundant water from last winter will likely result in a carp boom in the near future.

"We will probably never get rid of them. We've tried a lot of techniques, but so far nothing has worked. We are considering building a series of levees, but that idea is controversial," he says.

Eradication efforts can work in smaller, closed systems. Bajer worked on several projects in Minnesota where the lake was lowered and the surviving fish poisoned. It's a lengthy and sometimes expensive process, but in the right situation, it can be effective.

"We've learned a lot about common carp and efforts to control them, but there are still a lot of things we don't know," says Bajer.

Even less is known about the long-term impact of America's newest carp problem. Bighead and silver carp are best-known for their tendency to leap from the water when spooked. Search "jumping fish" or "flying carp" on YouTube and you'll be greeted with countless videos of massive schools of carp jumping as a boat runs across the water.

The only good news, says U.S. Geological Survey fishery biologist Dr. Matt Neilson, is that silver and bighead carp are filter feeders that primarily eat plankton. They don't root on the bottom or eat aquatic vegetation or invertebrates as much, which means they likely aren't having as direct an impact on ducks.

"They are mostly found in river environments, although they can do well in lakes," says Neilson. "The fact they eat plankton means they probably aren't having much impact on waterfowl habitat."

He says researchers are working to develop a selective piscicide that only affects larger filter feeders like silver and bighead carp.

"It's still very early, but it does show some promise," he says.

Scientists are also developing a toxin aimed at common carp, according to Bajer. It is delivered via a pellet that native fish won't eat. Other control methods have been fine-tuned, as well.

"We can actually train carp to come to a specific area just by feeding them. Once we get a large number to congregate, we can net them and remove them from the system. We also are using implanted GPS transmitters to locate fish in the winter. They gather in large schools in some waters, which means if we can find one, we likely found a large number," says Bajer. "We are probably never going to completely eradicate them, but we are getting better at controlling them."

He added that if their numbers are kept low, common carp can coexist with waterfowl. The threshold seems to be around 25 pounds per acre.

"I've seen it around 450 pounds per acre, which seems to be their maximum carrying capacity," adds Bajer.

Native fish like bluegills and perch are also somewhat effective at keeping common carp numbers in check in some waters. A single bluegill can eat thousands of carp eggs or fry. However, shallow lakes don't support many native fish because oxygen levels sink in the winter. Managers have found that aerating lakes helps native fish survive, which means carp numbers are held at a manageable level. Aerators cost money, though, and with common carp in so many lakes, it's impossible to treat every one. In other words, carp are here to stay.

PASS SHOTS

David Hart

HALF-A-MILLION $$ HONKER

A sleeping Canada goose decoy by a little-known carver is expected to bring at least $500,000 at auction. The decoy, carved in 1910 by Massachusetts cabinet maker Charles Safford, was called "an undisputed masterpiece and one of the greatest of all American decoys" by the auction company. The highest-selling decoys, a pintail drake and a preening Canada goose, sold for $1.13 million in 2007.

OPEN SEASON ON CRANES

A number of conservation groups are urging the Michigan Natural Resources Commission to approve a sandhill crane season. The USFWS authorized 2,002 of the birds to be killed under depredation permits in 2013, sparking talks of opening up a hunting season. The plan would have to get approval from the USFW$.

GAINING GROUND

The Louisiana Delta is no longer losing the oft-cited football field per hour. Instead, it's now a football field per 100 minutes, according to a new U.S. Geological Survey report. It credits conservation measures, but also says the lack of a major hurricane in nearly 10 years. A reduction in oil and gas activity has also helped slow the loss.

SO LONG DUCKS

The Army Corps of Engineers will no longer draw down Oklahoma's Kaw Lake so the state wildlife department can conduct aerial millet seeding to attract waterfowl. The popular program resulted in as many as 2,000 acres of millet on shallow flats. The Corps cited a required and costly National Environmental Policy Act study to continue the program. Seeding can take place during periods of natural fluctuations.

FIFTH FLYWAY

Joe Genzel

WELCOME TO THE '90s

To the chagrin of grandads across Pennsylvania, the state is finally allowing duck hunters to use spinners and other electronic motion decoys. The fear was that too many birds would be killed because of the advantages a Mojo or Lucky Duck afford. We don't have any science on this or "facts," but we're pretty sure some of the greenheads PA hunters are chasing have seen a spinner or Wonder Duck (and successfully avoided them) as they wing their way down the Atlantic flyway each fall. So welcome to the late 1990s Pennsylvania. We're sure Mojo's Terry Denmon is happy to have you aboard.

HONK IF YOUR ...

It seems these days we're all searching for ways to de-stress, and for city-dwelling duck hunters, some good news is on the horizon. Research conducted by a university in South Korea conceded the duck quack would be a superb replacement for the car horn. After testing 100 people at random, the quack was reportedly the most friendly to pedestrians. Better not test the prototype near Stuttgart though ... our Hyundai might come back with a few holes in the hood.

GET A CLUE

A Minnesota newspaper columnist laid a big honking goose turd in a July edition of The Star Tribune. Boiled down, his argument was the USFWS and biologists are basically lying to all of us about the status of the duck population. And he based that on the fact he's not killing a lot of ducks where he hunts in Minnesota and mallard harvest are down in Michigan, Wisconsin and his home state. He also said our seasons are too long and bag limits too liberal. We politely object. WF staffers have hunted all four flyways or the last several years, from Canada to Mexico. It's plain to see there are plenty of ducks, it's just a matter of the weather being right. Maybe if the marsh you've been going to since you were a kid isn't producing like it once was, go somewhere else? Just an idea.

FOWL FACT

Did you know ducks have few nerves and blood vessels in their feet? Which means they can't feel much cold, and why you see them sitting comfortably on Ice.

BY THE NUMBERS

$1

Cost of the first U.S. duck stamp, Designed by J.N. "Ding" Darling.

21,000 ft.

Altitude a plane once struck a mallard over Nevada.

1,000,000

Acres of bottomland Hardwood DU has Restored in the Mississippi Alluvial Valley.

11

Months a Texas man will spend in federal prison after violating the terms of his probation for killing two whooping cranes. The violation? Hunting from a roadway With an AR-15.
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Title Annotation:CONSERVATION CORNER
Author:Hart, David
Publication:Wildfowl
Date:Sep 29, 2017
Words:1882
Previous Article:Glory days.
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