Study Looks at Natural Productivity Issues
Hatchery steelhead spawners are unlikely to contribute measurably to the natural productivity of a mixed population of hatchery and wild fish unless natural spawner abundance is generally below carrying capacity, according to a new study.
D. Brent Lister, a consulting fisheries biologist in British Columbia, studied the census data of six Columbia River populations of summer steelhead, all with mixed populations of hatchery and wild steelhead, and published his findings, "Natural Productivity in Steelhead Populations of Natural and Hatchery Origin: Assessing Hatchery Spawner Influence," in the Jan. 9 Transactions of American Fisheries Society.
The steelhead populations he studied were from the Deschutes, Warm Springs and Umatilla rivers in Oregon, the Yakima River in Washington, and Joseph and Little Sheep creeks, tributaries of the Imnaha River in northeast Oregon.
Ever since Columbia and Snake river steelhead were listed as threatened under the Endangered Species Act in late 1990s, biologists and ecologists have worried about the threat of spawning hatchery fish on spawning native or wild steelhead, Lister said.
However, other than DNA analyses over the last eight years, any negative impact of hatchery on wild steelhead had not been shown.
So, the purpose of the study was to determine the influence of hatchery steelhead spawners on the productivity of natural spawners in populations in mixed stock streams.
Hatchery and wild steelhead spawners can interbreed when both are present. Although hatchery steelhead produced from native broodstocks can exhibit reproductive fitness approaching that of natural spawners, over the long term as hatchery fish are further in time from their broodstock origins, "the presence of less-productive hatchery spawners may therefore result in reduced population productivity estimates."
That has led to such initiatives as one proposed by the Washington Department of Fish & Wildlife in December. The WDFW proposal is to eliminate the release of all hatchery-raised steelhead on the East Fork Lewis River and the North Fork Toutle/Green River watershed as early as this year in order to "preserve key wild steelhead populations by minimizing interference by hatchery-produced fish." (CBB, Dec. 6, 2013, "WDFW Proposes Ending Steelhead Hatchery Releases In Three Columbia Tributaries To Boost Wild Fish"
Lister has been working on this research since 2005, when he received funding for the study from the Yakima Basin Joint Board, a coalition of irrigation districts in central Washington near Yakima.
What he found while studying census data of summer steelhead was that if the native population is at carrying capacity, the presence of hatchery spawners has a minimal impact on later adult returns. In fact, five of the six streams and populations he studied contained apparent healthy stocks of wild steelhead that Lister believes were operating at or near carrying capacity.
The Deschutes River, for example, has a high incidence of stray hatchery fish. As the Columbia River water heats up in the summer, these fish will move up into the cooler Deschutes River. Many will stay and spawn, some will find their way back to the mainstem Columbia River to move up to Columbia River and Snake River hatcheries upstream from the Deschutes River.
Even with the numbers of hatchery fish present, Lister found no net impact on natural production.
"Despite five generations of exposure to stray, multiple-generation hatchery spawners of local and nonlocal origin, there was no apparent effect on Deschutes natural steelhead productivity and status," he wrote.
He came to the same conclusion in the Umatilla River, as well as the other rivers in the study, with the exception of Little Sheep Creek. Little Sheep Creek, along with the Umatilla River, are watersheds where hatchery supplementation is taking place.
"If there is not a full complement of wild spawners, however, the hatchery fish can gain a foothold," he said. That is what he saw in Little Sheep Creek, where hatchery spawners were 73 percent of the spawning steelhead, but contributed just 44 percent to mean productivity while wild spawners contributed 56 percent to productivity.
The study is available at the American Fisheries Society website.
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