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Study: Barged Snake River Fall Chinook Juveniles
Stray More Than In-River Fish When Return As Adults

by Staff
Columbia Basin Bulletin, December 16, 2016

(Brandon Cole photo) Barge on Snake river transporting juvenile salmon. Barged juvenile fall chinook salmon from the Snake River may be missing important imprinting opportunities, especially at the confluence of major rivers, and so tend to stray more as adult fish as they home back to spawning areas or hatcheries.

A recent study suggests that experiencing first hand a river confluence, such as the confluence of the Snake River and Columbia River, is important in allowing fish to form a navigational waypoint for the return migration to the Snake River.

The study drew on a pool of nearly 4 million juvenile salmon PIT-tagged at hatcheries over multiple years and followed them as they were either left in the river to migrate to the sea, or were barged from three Snake River collection facilities, or from McNary Dam (the facility is no longer being used as a collection point), and then as they returned as adults.

The study evaluated the effects of hatchery (initial rearing location), the age of the juvenile salmon at release (yearling or subyearling), migration distance (distance from the hatchery to the release point for juveniles), whether the juvenile was barged or left in the river, and temperature and flow of the river on the return journey on two types of straying.

For those fish that returned but strayed while still in the lower and middle reaches of the Columbia River and downstream of the confluence with the Snake River (one type of straying), barging from Snake River dams was an important factor along with temperature (the odds of straying doubled with each degree in lower Columbia River water temperature).

Many juveniles left in the river when migrating also strayed in the lower Columbia River. However, these fish were more likely to eventually find their way to the Snake River than the second type of barged fish, according to lead researcher Morgan Bond, fishery biologist with the School of Aquatic and Fishery Sciences at the University of Washington.

Fish barged from the Snake River dams and ending up in Columbia River reaches upstream of the Snake River – the second type of straying – were 10 to 20 times more likely to stray than if the fish had been left in the river as juveniles. Almost none of these adult fish ever make it back to the Snake River.

The two types of straying are distinct, Bond said, because the latter type of stray, fish that pass the Snake River but keep moving up the Columbia River, have the opportunity to detect Snake River water, while the former stray before ever reaching the Snake River.

"Interestingly, fish transported from McNary were no more likely to stray than fish migrating in-river, indicating that fish being barged through the confluence are not imprinting that signal as a waypoint for the upstream migration," Bond said. "It seems clear that fish passing the Snake-Columbia river confluence and continuing up the Columbia are true strays because almost none of them successfully return to the Snake."

Nearly all of the strays in the lower river are temporary strays that eventually find their way to the Snake River. That indicates "that dipping into tributaries for thermal refuge may be important for Snake fish," Bond said. "Those fish that disappear in the lower river may be temporary strays that are more exposed to fishing or other sources of mortality while they wait."

The study, "Combined Effects of Barge Transportation, River Environment, and Rearing Location on Straying and Migration of Adult Snake River Fall-Run Chinook Salmon," was published online December 2 in Transactions of the American Fisheries Society.

Bond's co-authors are Thomas Quinn, professor, School of Aquatic and Fishery Sciences at the University of Washington; Andrew Dittman and Tiffani Marsh, research fishery biologists at NOAA Fisheries Northwest Fisheries Science Center; Peter Westley, assistant professor, College of Fisheries and Ocean Sciences, University of Alaska; and Dean Holecek, fisheries biologist with the U.S. Army Corps of Engineers, Walla Walla District.

This isn't the first study looking at the effects of barging on straying propensity or on the effect of temperature on straying. But, most others have drawbacks, Bond said.

"Now, with the advent of large scale PIT tagging from a number of hatcheries over several years, a "natural" experiment of sorts allows us to evaluate the relative effects of many of these variables simultaneously," he said.

Among the findings for fish that strayed in the lower Columbia River are:

"Strays are only likely to be problematic to local populations if they form a large proportion of the adults in specific spawning reaches," the study said.

Among the findings for fish that strayed upstream of the Snake River are:

Other findings are:

If fish are allowed to migrate in-river through the confluence, then they will be less likely to stray than those that are transported from the Snake River itself, Bond said. Yet, the survival benefits of transport may outweigh those effects.

"This is difficult to evaluate because survival of in-river migrating juveniles through bypass, spill, or powerhouse continues to improve and the survival benefits of transport are not as great as they once were," he said. "Although fish transported from the three Snake River dams are 10-20 times more likely to stray than in-river migrants, the overall rates of straying are still fairly low, likely less than 1 percent of the upper Columbia River return."

Still, research by co-author Dittman that evaluates the specific physiology of in-river and barged migrants hints at an impairment of barged fish to imprint while in the barge. Juveniles apparently log a series of waypoints as they move downstream and barged fish do not appear to log the confluence.

"This is encouraging because it does indicate there may be an operational change that could better mimic migration," Bond said. "So, I think that long-term the increase in in-river survival will have a larger impact on continued barge operations."

Related Pages:
Barges Carry Anglers' Hopes by Staff, Lewiston Tribune, 2/8/90

EPA Partially Oks State Standards for Toxic Pollutants in Washington Waters, Adds Federal Rules
Columbia Basin Bulletin, December 16, 2016

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