Study Finds Similar Fish Survival In Fraser, Columbia Rivers

NW Fishletter #254, November 10, 2008

A fish survival study published two weeks ago that found young chinook fared no better in a river without dams has rocked the popular media and led some fish advocates to question the validity of such work.

Tracking fish from a tributary of Canada's Fraser River with acoustic tags and detection arrays at the mouth of the river, 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 km north of the Columbia, where about 30 percent had made it, according to the study.

The Canadian chinook, which traveled 340 km to the mouth of the Fraser, showed survivals estimated from 4 to 67 percent.

"When considered separately by river section," said the study, "survival of Snake River smolts through the eight dams comprising the impounded section of the river down to Bonneville Dam was higher (chinook) or statistically indistinguishable (steelhead) from the survival for the entire Fraser River. For both species, survival in the free-flowing lower section of the Columbia River was higher than the entire-river estimate for the Fraser River."

Of course, researchers and policymakers involved in Columbia Basin fish recovery efforts have been aware of these results for years; it's just the first time they have been published in a peer-reviewed journal. The study appeared in PloS-Biology, an open-access publication from the Library of Science.

Canadian researcher David Welch, principal author of the study, had made several presentations before the Northwest Power and Conservation Council about his research, partly funded by BPA that included building a series of receiver arrays to track smolts on the Continental Shelf up to southeast Alaska.

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.

In late 2006, he made a special plea before the Council after some basin fish and wildlife managers and the state of Oregon had pushed to cut his funding in half. At that time, Welch discussed some of his other findings, including evidence that Snake spring chinook smolts seemed to show higher survivals than fish from the Yakima River.

In July 2007, Welch presented the initial results of his latest Fraser/Columbia comparisons at a workshop convened by the NMFS Science Center in Seattle. At the same time, California researchers announced preliminary results of their own work on Sacramento River fall chinook, where freshwater survival was in the 2-percent range.

NMFS is considering an ambitious project that would compare survivals in the three river systems, despite the significant hydrological and biological differences between them. In that context, Welch's latest study may garner a closer look from regional salmon managers, who have never liked his findings, since some raise serious doubts about the latent-mortality hypothesis long embraced by some regional agencies and tribes.

Already, some critics have raised rather bizarre questions about fish survival in the Fraser. USFWS 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.

However, Mike LaPointe, chief biologist with the Vancouver, B.C.-based Pacific Salmon Commission, told NW Fishletter that he was not aware of any juvenile fish problems in the Fraser that could be traced to the beetles.

In fact, LaPointe noted that sockeye migration from one of the Fraser's largest lakes doubled in 2007 from previous highs in the 1990s to 78 million smolts, and with improved ocean conditions, biologists are expecting exceedingly good returns next year.

He also said that the Fraser estuary doesn't seem to exhibit the high levels of predation on smolts by birds and pikeminnow like the Columbia River below Bonneville.

The Welch study, though suggesting survival levels in the two rivers were now similar, pointed out that "it remains unclear whether the similar rates of survival we measured result from past efforts to improve hydropower operations and reduce predators in the Columbia, or from unidentified problems in the Fraser River."

The study said it "seems likely" that poor survival to adulthood for stocks in both rivers was due to the common effect of ocean conditions.

In a response to an Oct. 29 editorial in The Oregonian that suggested dam passage had improved, Witt Anderson, director of programs for the Corps of Engineers' Northwestern Division, concurred.

"We agree that significant investments are being made to improve fish survival in the Columbia River Basin," he said.

"The range of measures in the newest plan for fish in the Columbia River Basin reflects fundamental changes in how the hydropower dams are operated. These measures, which run to 2018, build on remarkable progress in not only how the dams are operated to make them more fish friendly, but in the physical structure of the dams themselves. This is a huge change since the first court rulings in 1994," Anderson said

For years, NMFS scientists have noted in their annual reports on juvenile survival that passage through the hydro system with eight dams in place has equaled earlier survivals when only four dams stood between Idaho fish and the ocean.

The following links were mentioned in this story:

Survival Of Migrating Salmon Smolts In Large Rivers With And Without Dams