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NW Fishletter #387 Nov. 5, 2018

[3] DNA Shows Northern Pike Likely Planted Above Lake Roosevelt

Some northern pike populations in the Pacific Northwest have spread naturally, getting flushed downstream during high flows, or migrating upstream to populate new areas. But others--including the one that most threatens salmon in the Columbia River Basin--were illegally transported there by people.

Those are the conclusions of environmental DNA work being conducted by Kellie Carim, aquatic research biologist at the National Genomics Center for Wildlife and Fish Conservation in Missoula, Mont.

Carim presented her work to the Northwest Power and Conservation Council's Fish and Wildlife Committee on Oct. 9. It was one of three presentations related to salmon predators in the Columbia River Basin, with a focus on northern pike.

Using genetic tests to trace the most likely parentage, Carim determined that the 104 northern pike sampled from the Pend Oreille River, Box Canyon Reservoir and Lake Roosevelt did not likely spread there from upstream locations. Instead, the northern pike in these three areas were most closely related to pike found in Idaho's Medicine and Cave lakes.

If pike are drifting downstream, she said, they would be most closely related to the nearest neighboring populations--from Lake Pend Oreille and the Clark Fork River--and these were not.

Additionally, Carim said, the pike now threatening salmon in the Columbia River Basin appear to have links to other sources, further suggesting human transport from other locations.

The finding is both good news and bad news, she said. Good news because, while northern pike are spreading on their own, they aren't spreading as rapidly as would be the case if all the populations were related and spreading naturally. "It's not a steady stream of fish coming into these areas," Carim told the committee. "These fish are moving slowly. We have time to make a strong, concerted effort" to eradicate them.

The bad news is that people continue to distribute this sport fish into new areas, presumably in an attempt to establish new sport fishing opportunities. And, they're planting them in new locations even though the pike in Lake Roosevelt--the reservoir above Grand Coulee Dam--and in areas upstream are basically inedible due to high levels of toxins. In the Pend Oreille River, the Washington Department of Health has issued a fish consumption advisory, recommending no consumption of northern pike larger than 24 inches, and no more than two meals per month of fish smaller than 24 inches.

When asked, Carim suggested, "We're going to have to put a lot of emphasis on informing people" about the detrimental impacts of moving northern pike to new locations. "To prevent it from happening again, we're going to have to put some effort there."

Northern pike were first discovered west of the Continental Divide in 1953, after they were transported by people from Sherburne Lake in East Glacier, Mont., to the Lone Pine Reservoir in western Montana, Carim said.

From there, they spread to the Clark Fork, Flathead and Bitterroot river systems. Carim said there was a "human assist" in their continued spread into the Coeur d'Alene River, where, by the late 1970s, they spread farther downstream.

Their distribution didn't change much until 1997, when pike emerged in Lake Pend Oreille, she said. "It's believed a large flooding event flushed them downstream from western Montana into Lake Pend Oreille." Then, in 2004, they showed up in the Pend Oreille River, and moved into the Columbia River in Canada, and later into Lake Roosevelt.

Carim said northern pike are voracious eaters, and prey on other fish weighing up to 75 percent of their own body weight. "They could eat any one of our native fish out there," she said, adding. "The fear is that they're going to get out beyond Grand Coulee Dam and start impacting our native salmonids."

So far, fishery managers have had some success keeping this predator in check.

In a presentation to the full Council, Joe Maroney, director of fisheries and water resources for the Kalispel Tribe of Indians, discussed their efforts to control the predatory fish. Their goals, he said, were to minimize the pike's impact to native species, to reduce their spread to other waters including the Columbia River, and to reduce their numbers in Box Canyon Reservoir.

Maroney said when northern pike were first detected in Box Canyon in 2005, they were listed both as a prohibited species and as a game fish. The tribe successfully petitioned the Washington Department of Fish and Wildlife to remove them as a game fish, and keep them only as a prohibited species so it could attempt to eradicate them, he said.

After years of studies and surveys, the tribe initiated a full suppression effort in Box Canyon Reservoir in 2012, followed by a full suppression effort in Boundary Reservoir in 2017.

In Box Canyon, the tribe has set nearly 5,000 gillnets, and has reduced the number of pike captured from nearly 7,000 in 2013 to just 32 fish in 2017, Maroney said. He said the number jumped to just over 200 fish this year, but he believes that was due to a successful spawning and hopes that number will drop again next year. To date, the tribe has removed nearly 17,500 northern pike from the reservoir, weighing a total of 42,000 pounds. Suppression efforts in Boundary Reservoir have resulted in a notable reduction in total catch, dropping from 308 pike in 2017, to 121 pike this year.

He said it's too soon to know if pike will ever be fully eradicated from these two reservoirs, but the effort involved each year is reduced when fish numbers are reduced. At its peak, the tribe spent roughly two and a half months each year catching pike. Now, it takes just two and a half weeks, which significantly reduces their costs.

Maroney noted that northern pike are considered the top priority in Washington state for aquatic established species needing control or eradication. The Western Governors' Association has ranked them as seventh among all 17 Western states stretching from Texas to Alaska and Hawaii.

He told the Council, "Time is of the essence on this. One of the lessons learned is, if you find them, remove them. You don't need to study it to death."

Council members agreed. "It points out we ought to be spending an awful lot of time trying to convince fishermen not to transport them," Council member Bill Booth commented. Member Tom Karier added that he'd like more information about penalties for transporting non-native fish to new bodies of water. "It may be a small effort, but it costs millions of dollars and the penalties should be commensurate."

The Council also heard from biologists and managers at Chelan, Douglas and Grant county PUDs about their efforts to reduce other salmon predators, especially the unrelated pikeminnow.

As for northern pike, all three mid-Columbia PUDs are monitoring their areas to ensure early detection should the predator begin to inhabit their reservoirs.

These efforts include the use of environmental DNA sampling, or eDNA, which analyzes samples of water to determine if a species is present.

Some are also supporting suppression efforts upstream, and are involved in regional forums to remain updated on progress to eradicate them. -K.C. Mehaffey

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Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
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