More Dam Passage
by Bill Rudolph
Cumulative survival from Lake Wallula (in the Columbia River near Pasco) to Lippy Point ranged between 1 and 2 percent
for both groups in 2006, increased to 7 percent in 2008, and dropped to between 1 and 3 percent in 2009.
After tracking salmon smolts up the coast and detecting the survivors off the northwest tip of Vancouver Island, Canadian researchers have found no evidence that Snake River spring Chinook died off at a higher rate than fish that passed fewer dams on their seaward migration.
Published online in the April 1 Proceedings of the National Academy of Sciences, "Influence of multiple dam passage on survival of juvenile Chinook salmon in the Columbia River estuary and coastal ocean" chronicles the results of three years of tracking data from ocean-bottom acoustic arrays that tracked smolts from Idaho's Dworshak Hatchery and Washington's Cle Elum Hatchery on the Yakima River.
The expensive research was partly funded by BPA, which ended the project last year after spending more than $13 million on it since 2006, when the project was approved by the Northwest Power and Conservation Council.
"The new study reports that early marine survival of the Snake River population was essentially identical to the mid-Columbia population, despite the smolts passing through the Snake River dams," said a press release that accompanied the publication. "The lower adult return rates of Snake River Chinook therefore seem to be set later in the marine phase, sometime after the first month of life in the sea."
The paper itself speculates that "either that hydrosystem-induced mortality of hatchery-origin Snake River spring Chinook is greatly delayed or that differences in the subsequent ocean life histories influence survival of these genetically distinct population groupings."
The authors continued, "It remains unclear whether smaller, wild smolts have similar survival as the smolts reported here, although recent advances in transmitter miniaturization mean that it is now feasible to repeat these experimental tests using wild smolts."
Survival of both groups was similar in the Columbia River, the estuary, and on up the coast during the three years in the study, 2006, 2008, and 2009, the researchers found.
From below Bonneville Dam to the Willapa Bay array, 2006 survival was 78 percent for the Snake fish and 77 percent for the Yakima fish. In 2008 and 2009--when ocean conditions improved--survival ranged between 82 and 100 percent for both groups.
But survival in the freshwater plume ranged between 34 and 48 percent the last two years, which the authors said was "surprisingly low," given the short, 63-km migration distance and generally higher survival in 2006.
In 2006, by the time the smolts were detected at Lippy Point, coastal survival was down to 4 percent for the Snake smolts, and 2 percent for the Yakima smolts. But in 2008, coastal survival was an order of magnitude higher--29 percent for the Snake fish, and 30 percent for the Yakima fish. In 2009, when good ocean conditions had moderated, coastal survival declined to 12 percent for the Snake fish and 4 percent for the Yakima fish.
Cumulative survival from Lake Wallula (in the Columbia River near Pasco) to Lippy Point ranged between 1 and 2 percent for both groups in 2006, increased to 7 percent in 2008, and dropped to between 1 and 3 percent in 2009.
Earlier results from Kintama found little evidence for a differential mortality between barged and inriver smolts that were tracked to the tip of Vancouver Island. But critics say Kintama's smolt studies haven't used enough tagged fish, and that the fish they do use are too large to represent the runs at large. Up to now, the size of the tags has made the researchers pick larger fish in their studies.
"Although our new study does not remove all uncertainty concerning whether delayed mortality exists, it provides relatively definitive experimental results that delayed mortality does not exist in large hatchery smolts, despite their lower return rate," lead author Erin Rechisky of the Nanaimo, B.C.-based Kintama Research Services said in a statement. "We do not, as yet, know whether delayed mortality occurs in smaller, wild smolts; but if it does, the delayed effect of Snake River dam passage on survival must be large, because it is not found in the larger smolts we studied."
Rechisky pointed out that salmon population collapses have not been unique to the Columbia Basin, with others reported in recent years, from California to Alaska. Marine survival is considered one of the leading causes.
"Managers may need to adopt a more pragmatic view of what level of technical 'fix' to compensate for poor ocean conditions is possible within the Columbia Basin," she said, "because fluctuations in ocean survival are much larger than those occurring in freshwater. Our results are important because mitigation efforts in the Columbia River basin, which are partially based on the assumption that the effects of the dams on ocean survival are large, may be ineffective if the higher mortality of Snake River spring Chinook occurs in the North Pacific Ocean for reasons unrelated to dam passage."
Rechisky told NW Fishletter that, as the paper noted, spring Chinook smolts from both the Snake and the Yakima have been recovered in research surveys between the Columbia River and central B. C., and a Dworshak smolt was captured off central Alaska. But no Yakima fish were found in southeast or central Alaska waters. She said their own telemetry data has found only Dworshak fish off southeast Alaska. Data is skimpy, she noted, but differences in life history between the stocks could mean they occupy different parts of the ocean, which could lead to large differences in survival rates.
Rechisky said results from data collected in 2010 and 2011 are being finalized for a paper that will soon be submitted for publication. That paper will contain their latest analysis of both inriver and transported Chinook, which basically supports their earlier findings, she said. But the newer data also contain a more diverse complement of Columbia Basin stocks tagged over a longer time frame, with inriver fish tagged at Bonneville to reduce hydrosystem losses.
Results from Kintama's acoustic array research have clashed with some long-standing notions about fish survival before. A Kintama study that was peer-reviewed and published in 2008 found that young Chinook fared no better in a river without dams. It rocked the popular media and led some fish advocates to question the validity of such work.
The study, led by Kintama's president, David Welch, tracked fish from a tributary of Canada's Fraser River with acoustic tags and detection arrays at the mouth of the river. The researchers found hatchery spring Chinook actually incurred higher mortality rates per kilometer than spring Chinook traveling more than 900 kilometers down the Snake and Columbia rivers. In 2006, the U.S. fish were counted at a tracking array 40 kilometers north of the Columbia, where about 30 percent had made it, according to the study. The Canadian Chinook, which traveled 340 kilometers to the mouth of the Fraser, showed survivals estimated from 4 to 67 percent.
In December 2005, Welch presented the Power Council with initial findings from his 2004-2005 Fraser data that indicated Chinook survivals in the undammed B.C. river were similar to the highly impounded Columbia/Snake system.
After the study was published, critics raised rather bizarre questions about fish survival in the Fraser. U.S. Fish and Wildlife Service scientist Howard Schaller said it was hard to compare the two systems because of the large forest die-off in the Fraser watershed caused by bark beetles.
Fish Passage Center Director Michele DeHart told The Seattle Times that the study was an advertisement for Welch's POST array tracking system. She also brought up the beetles as a possible source of degraded water quality in another story about the study, posted at nature.com. -Bill Rudolph
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