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Research: Dams, Altered Environment Have
'Elicited an Adaptive Response in Snake River Fall Chinook'

by Staff
Columbia Basin Bulletin, April 12, 2013

Fall chinook salmon emerging from central Idaho's Clearwater River drainage may begin life under environmental conditions that prompts many to stall their journey toward the Pacific Ocean as juveniles and, as a result, return as adults in higher numbers than fish from other areas of the Snake River basin, according a recently published scientific paper from University of Idaho and NOAA Fisheries Service.

Fall chinook from the Clearwater, particular, seem far more disposed to overwinter downriver in the Snake and head for the ocean as yearlings, rather than streaming to the sea in spring or early summer as subyearlings.

The long-held theory was that Snake River fall chinook alsmost exclusively outmigrated as subyearlings. But within the last decade it has been determined that the Snake River fall chinook feature both type of life histories.

Pronounced disturbances, such as the construction of eight downstream dams that greatly changed the migrating conditions appear to have "Elicited an Adaptive Response in Snake River fall chinook," according to the article, "Spatial structuring of an evolving life-history strategy under altered environmental conditions" published online Feb. 20 in Oecologia.

Lead author is UI graduate student Jens C. Hegg. Co-authors are Brian P. Kennedy of the UI Department of Fish and Wildlife Sciences and Paul M. Chittaro and Richard W. Zabel of NOAA Fisheries' Northwest Fisheries Science Center.

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"Our results indicate that the yearling life-history strategy is predominantly represented within one of the main spawning regions, the Clearwater River, rather than being distributed throughout the basin," the paper's abstract says.

"Previous studies have shown the Clearwater River to have cooler temperatures, later hatch dates, and later outmigration of juveniles, indicating a link between environment and expression of the yearling life history. Our data suggest that this new yearling life history may be disproportionally represented in returning adult spawners, indicating selection for this life history within the population."

"Our data provide additional indication that, at least in the case of Snake River fall chinook salmon, Pacific salmon may have more adaptive plasticity than previously thought and that this plasticity may result in divergent migratory behaviors at the metapopulation scale," the paper said of the species' ability to adapt to conditions with natural selectivity, with the yearling life history perhaps winning the day.

"Because our study was limited to otoliths from returning adult fish, direct estimation of differential survival cannot be calculated. Still, we would expect the representation of yearlings returning to spawn would be greater if a higher probability of survival exists for this population," the paper says. "We found that 62 percent of returning fish had followed a yearling juvenile life history, a high percentage considering the Clearwater River provides only 36 percent of the total juvenile production for the Snake River basin (Garcia et al. 2008)," the research paper says.

"Connor et al. (2005) also noted that a large percentage of returning adults (41 percent) had followed a yearling life history.

"While this does not establish increased survival among yearling fish it provides evidence of possible selection for the yearling life history," the paper says.

The conclusions resulted from the chemical analysis of left sagittal otoliths from returning adult fall chinook salmon of presumed wild (natural origin), based upon a lack of marks or tags, that were collected over 3 years (2006--2008) during spawning operations at southeast Washington's Lyons Ferry Fish Hatchery. In each year, a fraction of the wild population (\10 percent) is randomly selected for inclusion in hatchery operations to maintain genetic diversity.

Otoliths -- sometimes referred to as "ear stones" -- are bone-like growths in the fishes' ears that add on a daily basis chemical recordings that allow researchers to track their movements by matching layers of the otolith with water chemistry, such as from the Clearwater or Snake, and saltwater from freshwater.

"Much of our information on juvenile origins, migration timing and journey comes from tagged populations of fish. However to understand the diversity of strategies of that small fraction of returning adults, you can never rely on getting enough returning tags to provide spatially explicit information. Therefore, we study chemical signatures in the otoliths that provide a 'flight recorder' of every adult that has made it successfully,'' Kennedy said.

The researchers "reconstructed the locations of individual fish at three major juvenile life stages to determine if the representation of the yearling life history was geographically structured within the population. We reconstructed juvenile locations for natal, rearing and overwintering life stages in each of the major spawning areas in the basin," the paper's abstract says.

"By combining individual migration data from otoliths with growth and survival estimates, we can begin to make specific predictions regarding the fitness advantages of observed migration strategies. Comparing the success of migration strategies under spatially heterogeneous environmental regimes may also inform our understanding of the relative contribution of evolution and phenotypic plasticity within Snake River fall chinook salmon.

"The results of this study have important implications for understanding the population-level responses to changing environmental regimes and anthropogenic impacts that may not be evenly distributed across their range," the paper says.

"Understanding the location and timing of overwintering and early spring outmigration of this population group may allow managers the opportunity to target management actions toward individual life histories within the population. Further study of the environmental factors acting on expression of multiple life histories may allow managers to predict and mitigate the survival and fitness consequences of climate change or other anthropogenic disturbances."

Research: Dams, Altered Environment Have 'Elicited an Adaptive Response in Snake River Fall Chinook'
Columbia Basin Bulletin, April 12, 2013

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