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NW Fishletter #394, June 3, 2019

[1] ISAB Finds Northern Pike Will 'Likely' Invade Rest of Columbia

A report by independent scientists says there are no easy solutions to dealing with the multitude of birds, marine mammals and other fish that prey on salmon and steelhead in the Columbia Basin. The analysis, requested by the Northwest Power and Conservation Council, found that current management focuses on individual predators, ignoring other factors that influence salmonid survival, including other predators.

The Independent Scientific Advisory Board warns that early detection and a rapid response plan are essential for dealing with northern pike, and recommends an ecosystem-based approach for evaluating predator impacts and control-measure effectiveness.

One of its main conclusions is that northern pike--a nonnative fish that can devastate salmon and steelhead populations--are likely to eventually make their way from Lake Roosevelt above Grand Coulee Dam to other parts of the Columbia River and its tributaries, where salmon and steelhead spawn.

The report recommends instituting early detection systems throughout the Columbia River, and developing a rapid response plan that can be employed immediately to try to eradicate the voracious fish when they do migrate--or are transported by people--downstream.

"Eradicating predators is extremely difficult and highly unlikely, especially in a big river like the Columbia River," ISAB member Stan Gregory told the Council May 8.

Showing a photo of a 17-inch northern pike and the 12-inch rainbow trout taken from its belly, Gregory said that the voracious predator--when it grows large enough--will eat bats, ducks, and salmon at all life stages, including adults. "They eat just about anything they can get into their mouths," he said.

Last November, the Council asked to ISAB to review the biological and economic impacts of native and nonnative predators in the Columbia Basin, including the effectiveness of predator management control efforts now underway, and specifically looking at potential threats of northern pike, which already populate Lake Roosevelt--the reservoir above Grand Coulee Dam--as well as other lakes and tributaries in the upper river.

The 159-page ISAB report includes a large section on northern pike, and concludes, "It is likely that even with the best efforts in public education, early detection, and control or eradication, pike will eventually invade the anadromous zone, either naturally or by human agents. Pike are likely to drastically reduce salmonid abundance, especially in low-gradient river segments with wide floodplains."

The report also notes, "Pike prefer salmonids and are capable of driving preferred prey species to very low levels or extinction," and, "All sizes and ages of pike (yearling and older) can eat salmon fry, parr, and smolts and reduce their abundance to low levels in habitats where they overlap."

Gregory told the Council that northern pike, a popular sport fish, were illegally transported to Montana in 1953 and have since moved west through illegal transplants and by migrating. "Essentially half of the spread has been caused by people, so managing people will be beneficial as well," he said.

They were first detected in Lake Roosevelt in 2007 and are now moving downstream about 25 miles each year, coming to within 10 miles of Grand Coulee Dam last year, he said.

With some funding from the Bonneville Power Administration (BPA), the Colville and Spokane tribes and the Washington Department of Fish and Wildlife have led efforts to control northern pike in Lake Roosevelt. This year, from May 6-9, they were joined by Chelan and Grant county PUDs, the Kalispel Tribe and the National Park Service in an intensive gillnetting operation throughout the 130-mile reservoir.

Gregory said that agencies would be wise to develop rapid response teams and plans that can act immediately to eradicate pike when they're first detected in new locations. Without immediate action, he said, it's unlikely they can be eradicated in the new area. He said by using eDNA--or environmental DNA--pike can be detected in water bodies through water sample analysis. Four sites just below Grand Coulee Dam will be monitored this year, along with numerous sites in Columbia River tributaries above the dam.

Once populations become established, control efforts must be extensive, riverwide, and continue indefinitely to be successful, he added.

Gregory also told the Council about a genetic approach that could be considered, but would take about 20 years before it would start to accomplish control of northern pike. The method would expose male pike to hormones that causes them to create two Y chromosomes instead of an X and a Y chromosome, he said.

So instead of giving an X and a Y chromosome to its offspring, it would provide only Y chromosomes. "That means when they reproduce with females, only males are born," he said. A population can then be reduced by reducing the number of females. Gregory said this is not a genetically modified fish, but a method used to control its sex.

In responding to questions from the Council, Gregory also said that spill to provide water for fish downstream and spring runoff over Grand Coulee and Chief Joseph dams are among the reasons why scientists believe northern pike will eventually make their way downstream, and into areas where salmon and steelhead spawn.

The ISAB did not discuss in detail the operations at those projects, he said, but a closer look at whether any changes can be made to delay natural migration is warranted.

In order to effectively control sea lions, birds or fish that prey on Columbia Basin salmon and steelhead, the Council should consider a basinwide analysis of the entire ecosystem, looking at both human influences as well as the natural systems, the study concluded

Gregory said that to understand which predators the Council should prioritize to help salmon and steelhead survive, or whether its current predator control programs are working, it's essential to understand the entire ecosystem and the impacts that its predator programs are having on the whole food web, not just the salmon or steelhead they're trying to protect.

The analyses must also include an understanding of how human activities are impacting the ecosystem and changing predator behavior, from riprap and development along shorelines to hydroelectric projects.

"It's a big task, but if you're only looking at one predator and one prey, you are going to get an incomplete picture," Gregory told the Council. He added, "You're managing a complex food web. If you take one species out, that doesn't mean you simply release your salmon and steelhead to go to the ocean." A salmon that doesn't get eaten by one predator may simply be consumed by another predator or die for other reasons later in its life cycle, he noted.

The report draws from several other examinations of the Council's predation programs, and reiterates a concern raised in a 2016 ISAB report. The new report repeats, "The ISAB considers compensatory mortality the most important uncertainty to address when developing a predation metric. Compensatory mortality occurs when predation mortality at one life stage is offset to some degree by decreased mortality at the same or subsequent life stages."

The 2016 report explains, "For example, a predator might eat injured or weak fish that would have died before reaching adulthood; therefore, controlling this predator would not result in more adult fish." And, "Loss of 50 [percent] of a juvenile salmon population in response to predation or other factors would likely reduce intraspecific competition for resources, potentially leading to increased growth and survival among the survivors."

As an example, Gregory noted, to know whether an angler reward program to control pikeminnow is working, the Council must also consider the pikeminnow's other prey and predators. Current efforts to control them reward fishermen for catching pikeminnows throughout the lower Snake and Columbia rivers, he noted, but their impact on juvenile salmon is much greater in pools below the dams.

"Does the sport-reward program still provide the best approach for removing northern pikeminnow and assessing possible compensatory responses? Or would more focused fisheries in selected locations be a more strategic and cost-effective method?" the report asks.

The report also says, "While it may seem intuitively obvious that reducing the abundance of a predatory species will benefit their prey, this is by no means always the outcome."

Currently, predator control in the Columbia Basin focuses on nine species--northern pikeminnow, northern pike, lake trout, Caspian terns, double-crested cormorants, ring-bill gulls, California gulls, California sea lions and Steller sea lions. Seven of those are native species and two are not.

These species represent just a small part of the entire food web, Gregory noted. Looking at just fish, there are 53 native freshwater species, 47 nonnative freshwater species, and 44 native marine species in the estuary. All are part of complex food webs with many predators and prey.

An assessment of the impacts of all potential predators throughout the basin will require integrated analytical tools, including life-cycle models, measuring smolt-to-adult returns, and density dependence analysis. The ecosystem-wide approach would identify locations where life stages of prey are most susceptible to different predators, and the relative benefits of decreasing mortality at different life stages.

In general, Gregory told the Council, protecting adult salmon and steelhead that are returning to spawn is more effective than protecting juveniles on their way to the ocean. But, he added, the ISAB cannot rank which predators would be most effective to control without an ecosystem-wide analysis.

The report does include two tables offering some guidance. One shows the relative vulnerability--high, medium and low--of juvenile salmonids to six bird and five fish predators. These relative rankings are shown for chum, pink, sockeye, coho, Chinook and steelhead. Another chart shows the relative vulnerability of adult and juvenile salmonids and eulachon, white sturgeon and Pacific lamprey to marine mammals, including California and Steller sea lions, harbor seals and killer whales.

The report also says that cost effectiveness of predator controls need to be included, and could modify decisions about which management actions to take.

The study is just part of the response to the Council's request for an analysis on predator management in order to help inform upcoming amendments to its Fish and Wildlife Program. The ISAB report will be followed by a companion report on specific predator-control programs and an economic analysis, expected to be presented to the Council in June. -K.C. Mehaffey

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NW Fishletter is produced by NewsData LLC.
Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
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