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Research: Barged Smolts Don’t Suffer From Transport, Issue Is ‘Accelerated Timing Of Ocean Entry'
Posted on Friday, June 15, 2012 (PST)

Juvenile salmon collected at dams and transported down through the Columbia-Snake hydro system aboard barges show no ill effects from that conveyance, according to a research paper published this week.


“Transported” fish survived as well as in-river migrants during the first month after they exit the Columbia River freshwater system, according “Estuarine and early-marine survival of transported and in-river migrant Snake River spring Chinook salmon smolts", which was published Monday in Nature Publishing Group’s open access journal, “Scientific Reports.”


“Despite tracking size-matched groups with similar ocean entry timing as far as northern Vancouver Island, 750 km beyond the last dam and for approximately one month after ocean entry, we did not observe lower survival for transported smolts,” the paper says.


“Thus, our results do not support the hypothesis that transportation-induced stress leads to higher mortality of smolts in the early marine period. It is likely that it is the accelerated timing of ocean entry which occurs during conventional transport practice that leads to differences in post-hydrosystem SARs [smolt-to-adult returns] typically observed between transported and in-river migrating spring Chinook smolts,” the research report says of previous research that notes lesser survival for transported fish.


“… altered timing of ocean entry for transported smolts, which arrive 2–4 weeks earlier than in-river migrants, may place them into less favourable ocean conditions.”


Lead author for the newly published research paper report is Erin L. Rechisky of Kintama Research Services Ltd., Nanaimo, British Columbia. Contributing authors include David W. Welch, Aswea D. Porter, Melinda C. Jacobs-Scott and Paul M. Winchell, all of Kintama, and John L. McKern of Fish Passage Solutions. The research was funded by the Bonneville Power Administration.


“This particular paper presents the result from our 2006-2009 differential delayed mortality study on whether or not barging reduces survival of transported smolts,” Rechisky said. “Our results indicate that barging itself does not negatively affect survival of smolts post-release, so transportation is successful but may reduce survival of the transported smolts by placing them into the ocean when early-season survival is poor.”


The full paper can be found at:



Many juvenile Snake River chinook salmon are transported downriver to avoid hydroelectric dams, predators and other perils in the Columbia River system. Mortality to the lowermost dam can be as great as 50 percent, so transported fish should return as adults at roughly double the rate of non-transported fish, the paper says.


“However, the benefit of transportation has not been realized consistently. ‘Delayed’ mortality caused by transportation-induced stress is one hypothesis to explain reduced returns of transported fish,” the paper says. “Differential timing of ocean entry is another. We used a large-scale acoustic telemetry array to test whether survival of transported juvenile spring Chinook is reduced relative to in-river migrant control groups after synchronizing ocean entry timing.”


Using a large-scale acoustic telemetry array, the researchers tracked the movements of size-matched groups of acoustic tagged, 1-year-old chinook salmon smolts reared at Dworshak National Fish Hatchery, which is located in west-central Idaho on the North Fork of the Clearwater River. The North Fork feeds into the Clearwater and then the Snake River just above Lower Granite Dam. Lower Granite is the uppermost of four federal dams on the lower Snake, which flows into the Columbia. The hydro system includes four projects downstream on the lower Columbia.


The tagged smolts were released by researchers directly into the river or transported by truck from the hatchery to the barges at Lower Granite and then barged more than 400 miles to a release point approximately six miles downstream of Bonneville Dam in 2006, 2008 and 2009. The researchers then used a telemetry data to estimate and compare post-hydrosystem survival. Bonneville is the last dam the in-river fish, as well as the barged fish, must pass before reaching the estuary and the Pacific Ocean.


“The use of acoustic tags allows survival to be directly estimated during seaward migration in the lower river, estuary, and early marine life phase where transport-related effects on survival are most likely to be expressed,” the paper says.


“In conventional transport operations, smolts are collected from dams in the Snake River and immediately barged downstream; therefore, transported smolts typically enter the ocean about three weeks earlier than their counterparts migrating in-river. For our experiment, we held transported groups at the hatchery until the in-river migrant groups were projected to arrive below Bonneville Dam, and timed their transport so release from the barge would roughly match the arrival of the in-river migrants at the release point below Bonneville Dam.”


As a test of their hypothesis that ocean-entry timing may play an important role in survival, a single group of acoustic tagged smolts was transported downstream on April 17, 2009, approximately five weeks earlier than the other two groups transported that year as part of the study.


“…survival of transported smolts that were released earlier, and therefore entered the ocean earlier, was only 58 percent of the delayed-entry transport groups. As estuarine survival was nearly identical, this survival difference occurred in the plume and coastal ocean,” the research paper says.


“A better understanding of the mechanisms causing differential mortality should lead to improved management decisions. The results of our study suggest that differential ocean entry timing is the most likely cause of D ratios less than 1, not transportation-induced stress,” the paper said of instances when transported fish produce lower SARs.


“Strategies such as delaying the start of transportation, or using ocean indicators, direct early marine survival estimates, and climate-based predictive models to potentially make real-time decisions as to when to start or end transportation may therefore be effective measures that could increase SARs for some Chinook populations.”


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