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Study:Stored Energy Levels Vary In Steelhead By Run, Sex, Time Spent In Freshwater, Hatchery Or Wild
Posted on Friday, February 10, 2017 (PST)

Levels of stored energy in steelhead differ according to sex, the amount of time spent in freshwater before spawning and whether the fish is of wild or hatchery origin, according to a recent study of steelhead that spawn in the Kalama River in Washington state.

 

The study, which based energy levels on the amount of somatic lipids in a fish, found that the lipid content depended on whether the steelhead was a summer – stream maturing – or winter (ocean maturing) fish.

 

Summer run fish, which return to freshwater months before spawning and mature while in the freshwater environment, had twice the lipid content than did winter steelhead, and, further, within each run the lipid level declined with arrival date.

 

In addition, summer run females had 19 percent more lipid content than males and wild fish had 21 percent more than hatchery fish, but the difference was greater for summer run fish than it was for winter run fish,

 

“Our findings highlight a fundamental difference between summer-run and winter-run steelhead that reflects the freshwater energetic demands of the two ecotypes and further describes steelhead diversity,” said James Lamperth, fish and wildlife biologist with the Washington Department of Fish and Wildlife. “Energy storage is likely part of a suite of adaptations associated with timing of return, rigors of migration, duration of freshwater residency, and spawning.”

 

Some of this is not new information. 2014 and 2015 studies found that chinook that arrive in freshwater long before spawning (premature migration) tend to have more stored energy, as do fish that migrate long distances to spawning grounds. But fish that differ in timing often migrate different distances, “confounding the ability to differentiate the importance of each factor on energy storage needs,” the study says.

 

However, with all populations – wild summer and winter runs and hatchery summer and winter runs – present in one river, the Kalama River, the authors were able to tease out the certainty of such statements about energy levels.

 

Multiple interacting variables, including return timing, rearing origin, and sex, were connected to levels of energy storage, as indicated by somatic lipid content, of steelhead returning to the Kalama River, WA, according to Lamperth.

 

“After controlling for migration distance, summer steelhead had more stored energy then winter steelhead; earlier arriving fish had more stored energy than those arriving later regardless of ecotype; wild fish tended to have more energy than hatchery fish; and levels of stored energy differed between the sexes and depended on the ecotype and most likely reflected future energetic demands of maturation,” Lamperth said. “Stable isotope analysis suggested these differences were not related to marine foraging.”

 

“Levels of stored energy but not marine foraging patterns differentiate seasonal ecotypes of wild and hatchery steelhead (Oncorhynchus mykiss) returning to the Kalama River, Washington” was published online in the Canadian Journal of Fisheries and Aquatic Sciences (http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2016-0018#.WJt4EPkrLIU).

 

Lamperth’s co-authors are Dr. Mara Zimmerman, research scientist, Washington Department of Fish and Wildlife, and Dr. Thomas Quinn, professor, School of Aquatic and Fishery Sciences, University of Washington.

 

Steelhead are a diverse lot with most spending one to four years in freshwater before migrating to the ocean and then another one to three years in the ocean growing to size. While they return to freshwater at all times of year, summer steelhead return from spring through fall and are relatively immature reproductively. They will overwinter as they mature and spawn the next spring.

 

Winter steelhead that return in late fall to early spring are relatively mature reproductively. They spawn weeks to a few months after returning to fresh water.

 

In addition, steelhead can spawn, survive the breeding season, return to the ocean and come back to spawn up to four times. Most of those that spawn more than once are females.

 

“Consequently, steelhead need to reserve sufficient energy for postspawning survival,” the study says.

 

Hatchery steelhead are not allowed to return to the ocean after spawning and may “inadvertently select for reduced energy storage because artificial spawning eliminates selection for dominance displays, nest preparation, and other energetically demanding behavior patterns associated with spawning,” the study says. Since they are killed before they can spawn, “there is no selection to store energy to spawn multiple times in a single year or to spawn in multiple years as occurs in wild fish.”

 

That also “might be part of the complex of traits that cause hatchery-origin salmonids to produce fewer offspring when breeding in rivers compared with sympatric wild fish,” the study concludes.

 

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