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Scientists, Ranchers, Greens Come Together to Tackle Invasive Carp in Oregon

Fish endanger bird populations on the Pacific Flyway

Malheur National Wildlife Refuge, in the heart of Southeast Oregon’s Harney Basin, could well be described as the middle of nowhere. But for migratory birds it’s a hub as important as Chicago’s O’Hare International Airport. Malheur supports more than 320 species of birds, including anywhere from 5 to 66 percent of the Pacific Flyway’s migrating waterfowl populations. Yet for more than 50 years the lakes of Malheur have been compromised by a scourge of introduced common carp.

Duck and carps Photo by flickr user llaurenIntroduced into lakes of Malheur National Wildlife Refuge about 50 years ago,
common carp inhibit the growth of aquatic vegetation and directly compete
with migratory birds by eating aquatic insects themselves.

Refuge biologist Linda Beck says the fish have drastically changed the ecology of Malheur’s lakes, reducing once-rich habitat to a “biological desert.” The carp’s bottom-feeding behavior stirs up sediments, inhibiting the growth of aquatic vegetation by preventing sunlight from penetrating the water and releasing nutrients that can cause algae blooms. Reduced vegetation supports fewer aquatic insects, which hungry migrants depend on. Carp also directly compete with birds by eating aquatic insects themselves.

“This habitat should look like the Florida Everglades,” Beck says. “But now birds mostly stay on the fringes.”

Until recently the only recourse was to poison the carp with Rotenone, a broad spectrum pesticide classified as moderately hazardous by the US EPA. This “solution” killed most fish for the short term, but after a few years their numbers would inevitably rebound.

Now there might be hope for a more sustainable approach. The refuge recently completed a Comprehensive Conservation Plan (CCP) that will guide its management for the next 15 years. The CCP was developed through a collaborative process that brought a range of stakeholders — scientists, ranchers and farmers, elected officials, environmental groups, and members of the Burns Paiute Tribe — together with refuge staff. The CCP’s top priority is to improve aquatic habitat, largely through controlling carp.

The Harney Basin consists of a series of low-lying freshwater wetlands, the largest of which is Malheur Lake. It’s a dynamic system fed by the Donner and Blitzen River to the south and the Silvies River to the north, subject to droughts and periodic flooding.

“I’ve seen the wetlands shrink to 200 acres one year and expand to 60,000 acres the next,” says Gary Ivey, who served as refuge biologist from 1983 to 1998.

By degrading habitat, carp reduce the carrying capacity of lakes and wetlands, especially for diving ducks like redheads, canvasbacks, ruddy ducks, and tundra swans. Several of these species nest on Malheur, but since carp were introduced, the number of ducks born on the refuge each year has declined from about 100,000 to between 50,000 and 60,000.

“You see a huge response after drought years or fish control years,” Ivey says. Following the last Rotenone control effort in 1992, peak counts of redheads and canvasbacks exceeded total population estimates generated by the Pacific Flyway midwinter survey.

The carp problem was sown a century ago, when the US Fish Commission started introducing Eurasian carp as a food fish in the late 1800s.

“The government was like Johnny Appleseed, planting carp everywhere,” Ivey says. Unfortunately, by the time people realized the carp’s potential to degrade habitat, it was too late. Common carp hold several advantages over most native fish: they’re long-lived, fecund, hardy, crafty — and large. “The biggest one I’ve had in my hands was 17 pounds,” Beck says.

Migratory birds Photo by Dan DzurisinFor migratory birds Malheur is a hub as important as Chicago’s O’Hare International Airport.

Today, more than seven million pounds of carp biomass infest the waters of Malheur National Wildlife Refuge. The CCP sets a goal of 100 pounds per acre or less as an acceptable threshold throughout the refuge. “In some areas total eradication just isn’t possible,” Beck says.

She and refuge staff are pursuing a multi-pronged approach for controlling carp, which could include physical barriers, biological controls and commercial fishing. A commercial operation would likely produce fertilizers or protein supplements for cattle. Next year refuge staff will launch an egg predation study to determine which of four fish species — two native, two localized — might become tools for carp control. They may recruit birds to help, too. White Pelicans flock to the refuge by the thousands to feed on fish but don’t breed there anymore, due to a dearth of suitable nesting islands. However, hundreds of Caspian terns have started nesting on a one-acre artificial island in Malheur Lake built by the Army Corps of Engineers. Sampling revealed that carp comprise 80 percent of the terns’ diets.

Beck calls Malheur Lake the Refuge’s number-one priority area. Whereas managers can control carp in smaller wetlands by draining them periodically, a large body of water requires a different approach.

Success on Malheur Lake will have implications for the entire Pacific Flyway. A 1981 survey revealed that two-thirds of wildlife refuges in North America consider carp a problem.

“Personally, I think they’re affecting 80 to 90 percent of our wetlands,” Ivey says. Improved habitat quality means Malheur can support more birds. And if successful strategies for controlling carp can be developed for Malheur, the techniques could be applied to other areas with carp infestations.

Just as refuge staff have embraced input and sought expertise from a wide range of sources, so too are they casting a wide net for funding projects. A coalition of groups has also created the Harney Basin Wetlands Initiative to secure funding for carp control projects in accordance with Malheur’s CCP. Carp can re-infest Lake Malheur via the Silvies River, much of which runs through private land.

“The initiative is an attempt to include the whole basin, not just the refuge,” says Ivey, who serves as Board President of the Malheur Wildlife Associates.

Beck welcomes the support. “Often with government plans there’s not a lot of implementation,” she says. “But we feel an obligation to our collaborators. They’ll be holding our feet to the fire.”

Juliet Grable
Juliet Grable is a freelance environmental writer based in Southern Oregon.

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