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Ecology and salmon related articles

Natural Fish Rule
at Redfish Lake

by Bill Rudolph
NW Fishletter, December 18, 2014

(Roger Phillips/Idaho Statesman) The Snake River sockeye salmon are the rarest of the Pacific salmon, an officially endangered species. More than 600 sockeye redds were counted in Idaho's Redfish Lake this year, and most were dug by natural-origin sockeye that returned in record numbers, the latest sign that the program to restore them is on track.

Some hatchery-origin adults were also allowed to spawn in the lake, but most were trapped for use in the captive broodstock program that started in 1999.

BPA has spent about $50 million on the broodstock project over the years, plus $13.4 million for a new hatchery and two years of operations at about $1.4 million, for a total of approximately $65 million.

This year's return was made up of more than 1,000 hatchery-origin and 460 natural-origin adults, according to a Nov. 24 statement from NOAA Fisheries. Last year, more than 500 redds were counted. In 1999, only 8 redds were tallied in the lake.

An article in the November issue of Fisheries recounts the history of the program, authored by two of the scientists most responsible for its success--Paul Kline of the Idaho Department of Fish and Game and Tom Flagg of NOAA Fisheries. The article describes how the program began with 16 anadromous adults, 26 residual fish (non-migrators), and 886 out-migrating smolts collected in the 1990s from Redfish Lake and nearby habitats. Two groups then raised fish in hatchery settings in Idaho and Washington, to reduce chances of a catastrophic loss.

According to the article, more than 10,000 adult descendants have been produced from those 16 wild fish.

"Although easily overlooked, a major program accomplishment was simply the development of fish culture protocols for rearing sockeye salmon full term to maturation," the article noted. "Earlier rearing attempts for various species of Pacific salmon and steelhead had suggested that captive broodstocks would have poor performance, with low egg survival, low egg-to-adult survival rates, and reduced size of captive-reared adults compared to wild fish."

The authors said that if those 16 wild adults returning from 1991 to 1998 had been released into Redfish Lake to spawn, "it is likely that the population would have gone extinct." Instead, the captive broodstock program has produced nearly 4 million smolts.

The article also reported that early data--from 1955 to 1964--showed that smolt-to-adult survival was 0.44 percent, during a period of fewer dams but intense fishing pressure. SARs for naturally spawning adults in recent years (2004-2006) have averaged 1.84 percent, nearly 3 times higher than SARs from smolt releases and more than 10 times higher than adult returns from pre-smolt releases.

The authors said the results have indicated that "properly scaled" smolt releases could produce enough adults (around 5,000) to recolonize the lake and juveniles from later spawning events could have the increased fitness needed to boost SARs "matching or exceeding self-sustainability," which indicates "that apparent 'extinction vortex'-type scenarios. . . could be reversible for this population."

The positive results have led managers to plan for production levels that could eventually lead to recovery. Their management strategy calls for using a higher proportion of natural-origin fish for lake spawning in high-abundance years, and a higher ratio of hatchery-origin adults in periods of lower abundance.

They noted that an estimate of carrying capacity for Redfish Lake in 2000 also supports the release of 1 million smolts into the region's lakes during the recolonization phase. Redfish Lake itself was estimated to be capable of producing nearly 500,000 smolts annually, and support an optimal escapement of 19,000 spawners. If a program was put in place to fertilize the lake, smolt abundance would more than double and optimal adult spawner numbers could reach nearly 47,000, the article said.

In the initial recolonization phase, the authors said, at least 10 percent of the natural-origin adults would be used in the broodstock program, and they projected an average of just under 5,000 sockeye to return from the ocean (647 natural and 4,347 hatchery adults) annually.

The article also noted that the expected food-web dynamics are "untested," partly because the lake also supports a kokanee population that began from out-of-basin plants in the 1920s, and competition for food could be an issue. Other researchers have noted that some heritable traits of the anadromous sockeye could give them a benefit when competing for food sources in freshwater.

In any case, the number of hatchery-origin spawners will be managed to stay below 30 percent, and once the stock has fully adapted, the captive broodstock programs will be ended, and the hatcheries managed as traditional "trap and spawn" operations where all juveniles will be released as first-generation smolts

But the article ends on a note of caution, recognizing that a downturn in productive ocean conditions might even lead to reimplementation of a captive broodstock program.

"We recognize that the ability of the Redfish Lake sockeye salmon population to sustain levels of abundance and productivity consistent with [National Marine Fisheries Service] delisting criteria is uncertain," the authors said.

"Though it remains our hope that demographic and fitness gains associated with program implementation will be long-lasting, uncertainties related to ocean productivity and climate conditions may result in population downturns that demand attention.

"If a decision is made to reinitiate short-term protective culture," the article said, "the tools and protocols we have developed in the present-day gene rescue program will help the next generation of managers, researchers, and fish culturists implement future actions."

IDFG's Kline told NW Fishletter by email that by analyzing SAR and age-structure data, his staffers expect 900 adult sockeye to make it back to the Stanley Basin in 2015.

Bill Rudolph
Natural Fish Rule at Redfish Lake
NW Fishletter, December 18, 2014

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