Researchers track Roosevelt’s kokanee, sturgeon and walleyes
Anglers aren’t the only people stalking fish in Lake Roosevelt. Researchers have several projects under way in the 130-mile-long reservoir using radio telemetry to plot movements of kokanee, walleye and sturgeon.
Walleyes have been followed as they hunker nearly 100 feet deep near the reservoir bottom during the day before rising to within 5 feet of the surface during night.
Kokanee, while they are schooling fish, also are surprisingly mobile. One kokanee implanted with a radio transmitter traveled at least 55 miles in a week last year between June 7 and June 15 as it went from Grand Coulee Dam upstream to the Hunters area. The next week it came back downstream to Whitestone.
White sturgeon, which range from the mouth of the Spokane River upstream into Canada, can be roamers or homebodies.
“Some move a lot and some don’t,” said Jason McLellan, Washington Fish and Wildlife Department fisheries biologist. He’s involved with several Lake Roosevelt studies, including some in cooperation with Indian tribes.
Key to much of the work are telemetry receivers attached to buoys that are anchored the length of the reservoir.
While McLellan uses the telemetry to seek answers about sturgeon survival in the upper reservoir, his wife, Holly McLellan, heads up Eastern Washington University research on kokanee and trout using the acoustic telemetry receivers in the lower reservoir.
The sturgeon research, ongoing since 2003, is geared to learning why the majority of young produced by these huge long-lived native fish are not surviving to adult stages.
“Our goal is to restore natural recruitment of white surgeon in the upper Columbia,” Jason McLellan said.
Researchers have documented major spawning areas, including two in Washington that were previously unknown.
From these locations and at least two in British Columbia, the sturgeon are producing viable eggs that hatch into free embryos. But somewhere around two weeks later, after the young sturgeon begin to feed, they disappear.
Fisheries biologists are keeping the population going by raising young sturgeon to survivable sizes and releasing them in the river.
Some speculate the young are being targeted by predators, including walleye, smallmouth bass and other non-native species that have taken hold in the river since the building of dams.
The theory is hard to quantify from stomach sampling since the tiny boneless sturgeon are digested very quickly.
But as they pore over the survival issue, the researchers are documenting that some adult sturgeon mill around a small area at Marcus Flats while other sturgeon zigzag through the area. Few sturgeon venture downstream past the Gifford area, although some make it to the mouth of the Spokane River.
A dozen walleyes implanted with transmitters in Little Dalles Eddy above China Bend were followed at the peak of sturgeon spawning in late June.
The researchers learned that during daytime the walleyes went to the deepest spots of the Columbia where the sturgeon larvae are. “That doesn’t necessarily mean they are eating them,” McLellan said. “However, we know that pretty much anything that has an opportunity will eat larval fish, including sculpins, suckers and rainbow trout.”
The impact hatchery-raised trout are having on native redband rainbows also is being studied.
All of the 750,000 net-pen-raised rainbows are adipose-fin-clipped before being released into Lake Roosevelt so they can be distinguished from native trout, he said.
Creel surveys conducted by the Spokane Tribe indicate that at least 10 percent of the rainbows anglers keep from Lake Roosevelt are natives, he said.
“The native rainbows spawn in different tributaries,” he said. “We’re trying to see if the harvest is hitting one stock more than another. If so, maybe we can improve management to even it out.”
Holly McLellan’s research focuses on the 17 buoys anchored every three miles in the lower third of Lake Roosevelt downstream from Lincoln, plus one below Grand Coulee Dam in Lake Rufus Woods.
For two years, researchers have been following adult wild kokanee implanted with transmitters. This year they’ll also be following hatchery kokanee, which are fin-clipped.
“A lot of anglers think the kokanee stay in the Spring Canyon area, but we’ve learned they don’t stay in one area,” she said. “They can move through the entire lower third of the reservoir in a week in early June.” However, they most commonly are in the lower 25 miles of the reservoir from Grand Coulee Dam up to Whitestone, she said.
The study will be looking closer this summer on the kokanee’s vertical migration. “There’s really no coldwater refuge in the reservoir during summer, since the water is basically the same temperature from top to bottom,” she said. “That could be a limiting factor for kokanee.”
This fall, researchers hope to get more information on spawning. About 500,000 fin-clipped kokanee are released into Lake Roosevelt each year by WDFW and the Spokane Tribe. However, “nobody knows where the wild kokanee spawn in Roosevelt,” McLellan said.
“We’ve assessed most tributaries and found some spawning, but we’re assuming that most of the fish spawn somewhere along the shoreline deep enough to allow for the reservoir’s huge drawdowns.”
Or maybe wild kokanee are all coming down from Canada, she speculated.
“Last year, we didn’t detect any movement that far upstream. The farthest one went was to the Wilmont area south of Hunters (in June). Then it came back down to the Whitestone area as water began to warm up.”
Only two of the study’s transmitter-equipped fish went over Grand Coulee Dam last year.
“It was interesting that they went down in on May 11 and May 25, not when the reservoir was being drawn down, but during the refill,” she said.
The researchers will follow the hatchery kokanee this year to see whether they stay where they are released or if they are more susceptible than wild fish to being flushed out of the reservoir.
“We stock the hatchery kokanee out of Fort Spokane and Seven Bays. Maybe we’ll learn that we should spread the releases to more spots and create microfisheries,” she said.
Research has already shown a payoff to raising net-pen kokanee to 9 inches before releasing them in late May.
“We’ve been releasing them at 7-8 inches, but we’ve found that anglers catch more of the fish if we raise them to 9 inches,” she said.