Study Compares Homing Rates
... strongly suggesting that juvenile transport impaired adult orientation
of both hatchery and wild fish during return migration
A new study indicates that Snake River spring/summer chinook salmon and steelhead transported downstream in barges as juveniles have more trouble than in-river migrants in finding their natal streams and passing dams when they return as adults to spawn.
The technical report, "Effects of Transport during Juvenile Migration on behavior and Fate of Returning Adult Chinook Salmon and Steelhead in the Columbia-Snake Hydrosystem, 2000-2003," was prepared for the U.S. Army Corps of Engineers. The Corps manages the dams and fish transportation program.
The study results show that on average juvenile chinook and steelhead that were barged as juveniles had "homing" rates to Lower Granite Dam as returning adults that were 10 percent lower than fish that migrated to downstream in-river. And barged salmon were 1.9 times more likely to fall back at dams as they make their spawning journey, and barged steelhead 1.3 times more likely, than in-river fish. A large share of the barged fish that did fall back through spill gates or other routes did so multiple times.
"The results were consistent between species and years, strongly suggesting that juvenile transport impaired adult orientation of both hatchery and wild fish during return migration," according to the report abstract. In-river migrants make their way down river through spill gates, turbines and mechanical bypass systems.
"Overall, the results suggest that the benefits of barging juveniles may be reduced due to negative effects on returning adults," the report says.
The study was authored by Matt Keefer, Chris Caudill, Christopher Peer, and Steve Lee, all affiliated with the Fish Ecology Research Laboratory at the University of Idaho, and by B.J. Burke and M.L. Moser of NOAA Fisheries' Northwest Fisheries Science Center.
The study can be found at: www.cnr.uidaho.edu/uiferl
The reduced homing and straying into other streams means fewer of the barged fish return to their natal stream, or hatchery of origin, to spawn than non-barged fish. That could undermine production for salmon and steelhead in those streams. Some of the stocks are listed under the Endangered Species Act. And it could affect genetics and fitness of stocks in streams where they stray.
"Proliferation of out-of-basin hatchery salmon and steelhead in lower Columbia tributaries could undermine recovery of listed wild fish (Levin et al. 2001), reduce natural productivity (Chilcote 2003), or have other poorly understood ecological consequences (Weber and Fausch 2003)," according to the report.
Assuming four million juvenile spring/summer chinook are transported, adult return rates of 0.5 to 2 percent, a 3.3 percent straying rate, and 11 percent harvest rate for transported chinook, "approximately 600 to 2,300 barged Snake River salmon may stray into other Columbia River tributaries annually, of which at least 400 to 1,400 (60 percent) would likely be hatchery fish," according to a calculation that the authors admitted was "imprecise." And from 2,000 to 8,000 transported steelhead might be expected to stray each year, of which would be hatchery derived.
Adult fallback at dams can bias fishway counts used for escapement estimates and to set harvest quotas. And repeated trips up and over the same dam slows migration and "can be associated with high energetic costs, pre-spawn mortality, and prolonged exposure to fisheries," the report says.
The researchers used radio-telemetry to examine the effects of juvenile transportation on adult "fate" and migration behaviors of 1,184 Snake River spring-summer chinook salmon and steelhead. All study fish were collected and tagged with passive integrated transponder (PIT) tags as juveniles at Lower Granite Dam on the Snake River from 1998-2002 and returned as adults during 2000-2003. About 60 percent of the adults radio-tagged in this study were transported in barges as juveniles from Snake River dams to release sites downstream from Bonneville Dam on the Columbia River.
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