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Removing carp from Lake Spokane mixes science, grunt work

Fri., May 19, 2017, 6 a.m.

Reducing the number of carp in Lake Spokane to improve water quality is not only rife with complications, it’s also ripe.

“Bring any extra clothing you’ll need on the boat – whatever you want to smell like a carp,” said Chris Moan, the fisheries biologist heading up a crew that’s gillnetting carp this month from the Spokane River reservoir behind Long Lake Dam.

As they prepared to launch and pull nets that had soaked through the night, stories were told about spouses who drew the line at the home driveway and directed all carp-related work clothing to the laundromat.

“You get used to it, but your family may not,” Moan said.

The first of two weeks being devoted to honing techniques for removing carp from Lake Spokane has ended and the nets are getting a one week break. Starting on May 8, nets were set for three nights, pulled the following days and all fish were tallied by technicians assembled by Avista and the Washington Department of Fish and Wildlife.

Totals for three nights were 550 carp and 117 northern pike caught and killed. Carp and northern pike are being removed and samples taken to better understand their origins and movements.

Pike are not specifically being targeted, state officials say, but since they’re classified as a prohibited species in Washington, they’re being removed if caught in the nets, which extend 10 feet up from the bottom.

The largest pike caught last week weighed 23 pounds and was 42 inches long. Small pike would go through the large net mesh. The largest walleye was 30 inches long and the largest carp was 32 inches long.

“One of the things we’ll be looking at is whether pike are reproducing in Lake Spokane or whether most of them are originating from North Idaho,” said Marc Divens, state warmwater fisheries research biologist.

The carp removal project is led by Avista as part of its federal relicensing agreement to improve water quality in Lake Spokane. Carp are notorious for stirring up lake bottom sediments as they feed.

Three years ago, Avista caught, radio tagged and released carp in a survey to determine where most of the carp congregate to spawn. That information is being used this year to help determine where the gillnets are placed, Moan said.

“We’ll never remove all of the carp in the reservoir,” he said, noting that the project seeks to learn when, where and how to focus efforts to greatly reduce the number of carp.

The project is still in the experimental phase to learn how to catch and remove the maximum number of carp with a minimum bycatch, said Tim Vore, Avista environmental specialist.

The nets being tested have a mesh stretch size of 5 and 8 inches, allowing most trout, crappie and bass to avoid being caught.

“The first night we put out eight nets, but that required a solid 12 hours of collecting and processing the next day, so we scaled back to four nets,” Moan said.

Many of the non-target species that are caught in the nets can be released alive, he said.

The highest bycatch in last week’s three nights of netting included large-scale sucker (63 total, 57 released alive), tench (55 total, 54 released alive), walleye (35 total, 18 released alive) and largemouth bass (20 total, 15 released alive).

Electro-shocking was also tried but with very poor results for carp, Divens said. The method involves cruising the shallows with a boat equipped with electrodes that deliver a localized shock that stuns fish so they can be scooped up by staff wielding fishing nets.

“The fish weren’t in the shallows and we caught very few carp that way,” Divens said.

The carp were in the pre-spawn stage last week while the pike that were caught appeared to be in the middle of spawning, with some of the female fish being full of eggs and others being spawned out, he said.

Zeroing in on the best period for putting out nets will be key to long-term carp management, Moan said.

The timing for the spawn depends of factors like water temperature that can’t be pegged to a calendar date because it changes every year, Moan said. “One of our challenges is scheduling a crew from Avista, University of Idaho, and Fish and Wildlife,” he said. “They all have other jobs and need lead time to be available.”

The 12-person crew is taking this week off and will return for three more nights of netting starting Monday, Moan said, noting that the carp may be more involved in spawning by then and easier to capture.

The crew, which stages out of the Suncrest private boat launching area, receives questions from anglers they encounter.

“Some want to know how many bass and crappie we’re catching,” one technician said, partly because they want to know where to go fishing and partly because they’re concerned that the project doesn’t hurt their prized panfish and largemouth bass fisheries.

“We’re not hurting those fisheries at all,” Divens said. “We’re catching more pike than we expected and we’re taking samples to determine several things, including if they’re spawning here or mostly coming down the Spokane River from Idaho.”

The nets also are catching more walleyes each year indicating the population is expanding, Moan said.

“Anglers are discovering that fishery,” Divens said.

Some anglers ask why the non-native tench bycatch is released alive back into Lake Spokane during the project since they’re not a favored sport or food species. Both tench and carp were introduced to Western waters as food fish in the 1800s because they could survive train travel.

But Westerners never acquired a lasting taste for tench or carp.

The project is geared to carp and there’s no cost-benefit to expanding it to tench, Divens said.

“It is generally thought that significantly reducing a tench population through mechanical removal is unfeasible,” he said. “Tench are widespread and do not pose the threat to the fish community, as do pike, or water quality issues related to carp.”

Others have asked if something useful could be done with the carp carcasses rather than hauling them to a designated landfill?

“In our Water Quality Attainment Plan, it was specified by Washington Department of Ecology that we dispose of the carp in a landfill that accepts PCB waste,” said Mary Tyrie, Avista spokeswoman.



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