The Washington Department of Fish and Wildlife will spend the next five years measuring the abundance, trends and consumptive impacts of nonnative fish in the Columbia River from McNary Dam to Priest Rapids Dam, in order to better inform efforts to control them.
Scientists say the fish may be consuming large numbers of juvenile salmon and steelhead in the Columbia River before they reach the ocean. State and federal agencies have done little to control these predators due to a lack of basic information about population sizes of introduced fish like walleye and bass or estimates of how many salmonid smolts they consume.
The study will use modeling to determine the impact of nonnative fish on salmon and steelhead that could eventually be used in other parts of the basin.
After revisions, their proposal recently won approval of the Independent Scientific Review Panel.
"We need a lot more information about the population dynamics of these nonnative fishes in the Columbia and Snake rivers. They've been very much overlooked, at least by the scientists," Andrew Murdoch, WDFW's lead scientist and science division manager for the eastern Washington fish program, told NW Fishletter.
He said WDFW biologists hope to begin gathering data this spring, using electrofishing to mark and recapture fish. WDFW Fisheries Biologist Matt Polacek, the project's primary proponent, is developing a biological assessment and hopes to get the go-ahead from NOAA Fisheries to work in the main-stem Columbia River without significantly impacting Endangered Species Act-listed species.
With a proposed budget of $284,843 per year, the study would redirect Bonneville Power Administration funds from a WDFW effort to reestablish kokanee in Banks Lake.
"This isn't new BPA money," Murdoch said. If approved, it would use current funding from a BPA-funded project that's being closed out, largely because the kokanee are getting consumed or out-competed by nonnative fish, Murdoch said.
WDFW initially proposed the study in 2020 and an ISRP review sent the proposal back, asking proponents to address seven concerns to strengthen the study. On Dec. 7, the panel determined that the proposal meets scientific review criteria, noting, "This proposal addresses significant predation threats that may limit survival and recovery of Endangered Species Act (ESA) listed salmon and steelhead in the Columbia and Snake river basins," the ISRP wrote, later adding, "The project is forward looking and could provide important information related to predator responses to climate change in the mainstem Columbia River."
In the new study proposal, project proponents recognize that nonnative fish are having negative impacts on ESA-listed salmon and steelhead in the Columbia River, and that a lack of knowledge is preventing further management of nonnative fish. According to the proposal, studies have concluded that predator fish in the Columbia River may be consuming 17 percent of the juvenile salmon each year. Another study found each walleye living in the stretch of river from McNary Dam to Priest Rapids Dam eats roughly 2.5 salmonids a day and each smallmouth bass eats about 1.3 salmonids daily.
Murdoch cautions that there are huge information gaps, especially in the long stretch of river above McNary Dam, which includes the mouth of the Snake River and the Hanford Reach. "We're trying to collect better data so we can make some informed management decisions, if warranted," he said.
In December, the Washington Fish and Wildlife Commission adopted a nonnative fish policy that attempts to balance popular sport fishing for species like walleye and bass with the impacts they have on native species—especially salmon. The new policy sets the conservation and recovery of native species as the state's highest priority, and directs fish managers to use the best science available to manage nonnative fish when it comes to their impacts on native fish.
But Murdoch said in a river the size of the Columbia, much of the data needed to make decisions on impacts of nonnative fish isn't known. WDFW currently has no size or catch limits for bass, walleye or channel catfish in the Columbia River, which enables more harvest of nonnative fish. The study proposal notes, "While these actions may reduce nonnative predator abundance, it will require a voluntary effort from recreational anglers." Murdoch said that may not be happening, as people who enjoy walleye and bass sports fishing often release their catch to allow them to grow larger and become more challenging to catch.
The study proposal notes that nonnative predator populations can be also reduced by ensuring failures in their spawning. Murdoch said that reducing the number of spawners will first require knowledge of where and when nonnative fish spawn—which is another gap in their data.
As part of the study, scientists want to compare the impact of nonnative fish to the native pikeminnow, which have been controlled for decades through fishing reward programs offered by BPA and Columbia River PUDs. Murdoch said scientists believe northern pikeminnow are no longer the primary or most abundant fish predator, and that there are now more walleye and bass in most reaches of the Snake and Columbia rivers. There numbers may also be increasing.
According to the project proposal, a 2019 study found the catch rate for smallmouth bass in the lower Columbia River was the highest on record in 2018 and walleye abundance was relatively high compared to prior years. Several studies in the John Day Reservoir found walleye and smallmouth bass have significant impacts on juvenile salmon abundance. Findings of a 2009 study "suggest that the overall impact of non-indigenous species on salmon recovery may meet or exceed the cumulative impact of the conventional 4-H's sources of mortality (e.g., habitat, hydro, hatcheries and harvest)," the study proposal stated.
But most fish predation studies have occurred below McNary Dam, so there are still large information gaps in the middle and upper Columbia River.
"Right now, we're just really focusing on their abundance, and we'll look at age and size structure, and specifically at consumption of salmon and steelhead smolts," Murdoch said.
But, he noted, the study will only show what these nonnative fish are eating during a few months of the year. That leaves many questions unanswered, including what nonnative fish eat the rest of the year, and how American shad and other species impact the food web.
"I would argue the research should not simply stop at salmon and steelhead," Murdoch said. "Ultimately, you have to understand the entire food web of these fish."
Murdoch said one of their primary concerns is whether the nonnative fish populations are expanding, and whether they will move into new areas now occupied by cold water fish as temperatures warm.
"Climate change related impacts on freshwater habitats will promote further population growth and range expansion of non-native predators into upper reaches of the Columbia River and major tributaries, which could potentially decrease the survival of juvenile salmonids," the study proposal states.
Murdoch said that the first few years of this study could be a starting point that leads to many different areas of research for understanding the Columbia Basin's food web. "As we get down this predation path, it gets even more complicated. Resident fish can live for quite a long time, and as they age and get bigger, their diets change," he said.
Predation by nonnative fish is just one of many risks that salmon, steelhead and other native fish face in the Columbia Basin, Murdoch noted, adding, "We think that it's the death of a thousand cuts, so how big of a cut is walleye predation? We just don't know."
Once scientists have a better idea of the relative impact that nonnative fish have, they can look at more management options, he said.
"We focus so much on salmon and steelhead. If we want to even begin to manage walleye and some of the other nonnative fish, we've got to learn what they've been up to for the last 50 years," he said.