A new study by researchers in Oregon and British Columbia has found that survival of juvenile salmon and steelhead during their migration from the headwaters to the sea down two large Northwest rivers -- the Columbia and the Fraser – is remarkably similar despite one major difference.

The Columbia River has a series of dams, while the Fraser has none.

"It is striking that our main finding, that survival is not worse in the Columbia despite the presence of an extensive network of dams, remains the same no matter how the data are analyzed," according the study, "Survival of Migrating Salmon Smolts in Large Rivers With and Without Dams."

The study's data shows that Columbia-Snake river survival matches or exceeds that of the Thompson-Fraser even when adjusted for migration time and distance. The Columbia-Snake fish travel about twice as far as the Fraser-Thompson salmon and steelhead from the study's starting points to the river mouths.

"This result is surprising, given that dams are often implicated as major barriers to recovery in the Columbia," the study says. "However, our data do not address whether the possible delayed effects of hydropower system passage subsequently affects mortality after the fish leave the river for the ocean, currently a contentious issue."

The researchers point out that there clearly are other differences between the rivers.

And though the study – which charts data from either acoustic and transponder tags implanted in fish-- found that the average mortality in both rivers was between 70 and 80 percent over a four-year period, the results should be viewed with caution.

"It came as quite a surprise to us that the Fraser River salmon populations studied have lower survival than the Columbia River study populations," says Erin Rechisky, one of the study authors and a PhD candidate in the University of British Columbia's Department of Zoology.

Rechisky said that there is not yet sufficient evidence to reach any conclusions.

"Clearly dams are not good for salmon. What is unclear is whether the Fraser River has a problem that cuts salmon survival to that of a heavily dammed river, or whether factors other than dams play a larger, unsuspected role in salmon survival."

The research paper was published this week in the journal PLoS Biology and can be found at http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0060265&ct=&ct=1

The open-access, peer-reviewed general biology journal is published by the Public Library of Science, a nonprofit organization of scientists and physicians that says it is committed to making the world's scientific and medical literature a public resource.

"Despite the obvious comparison, it would be overly simplistic to say that dams have no impact on smolt survival, because we know they do," said Carl Schreck, a professor of fisheries and wildlife at Oregon State University and the U.S. Geological Survey and an author of the study.

"There also may be some additional delayed mortality of Columbia River smolts caused by the stress of passage through the hydro system that is not manifested until the fish reach the ocean," Schreck said. Columbia River juvenile salmon can be stressed by navigating the series of eight dams from Lower Granite Dam on the Lower Snake River to the Columbia's Bonneville Dam.

Other stress-inducers can include water temperature, contaminants, predation attempts, and availability of food, forcing fish to channel their energy into survival instead of growth, Schreck said.

"Stress in fish delays development," he said. "It also suppresses the immune system, which can increase the chance that fish will be susceptible to disease or parasites. Even though these data suggest that the fish survive the freshwater phase of their migration, that kind of weakened condition can be the difference when a young salmon tries to adapt to a salt water environment."

The study's lead author, Canadian David Welch, said he is developing a separate research paper that investigates delayed mortality. The scientific team aims to clarify with future studies using Pacific Ocean Shelf Tracking technology whether dam passage in itself has long-term detrimental effects that impact salmon's ocean survival.

POST has established a series of "listing lines" -- arrays of acoustic receivers -- along the continental shelf from off the Oregon coast to southeast Alaska.

Welch said he and Schreck have differing opinions on delayed mortality. Welch believes failed adult returns are the result of conditions in the ocean more so than the existence of delayed mortality.

"That's an issue we have to address," Welch said of the extent, if any, of delayed stress mortality.

Welch too said that the study's message is not that dams don't affect salmon and steelhead survival.

"We all know that's not true," Welch said.

The report acknowledges that "modifications to dam design and operation have increased Columbia River smolt survival in the past 20 years."

"Our results suggest that survival through the hydropower system has now increased to levels similar to those experienced in both the undammed lower Columbia River and in the Fraser River…," the study says.

"There are several opposing inferences that can be made from our findings regarding the role of dams in preventing the recovery of salmon," the study says. "We suggest that conservation efforts in the Columbia may be better directed towards understanding the effects of hydropower system passage on ocean survival, in addition to the extraction of small gains in survival at the dams."

The researchers note that threats beyond the rivers are taking a heavy toll on salmon. These include habitat destruction, competition with hatchery fish, harvesting and large-scale changes in ocean climate.

Schreck's work during the past 36 years has centered on the causes of stress in juvenile and adult salmon and steelhead, and the impacts that stress can have.

During the past dozen or so years, OSU scientists have been using telemetry to study survival rates of juvenile salmon below Bonneville Dam. They discovered a high rate of mortality in the estuaries, which led to the surprising discovery of the impact of predation from colonies of terns. In 2000, OSU introduced the use of a new tool -- acoustic telemetry – for studying salmon on the West Coast. Acoustic telemetry allows the signals emitted from tagged fish to be picked up by underwater hydrophones in salt water, as well as fresh.

Welch subsequently established the listening stations along the continental shelf, and also began using the same acoustic technology used by OSU researchers to study the survival of smolts in the Fraser River.

The research team also included Rechisky, Michael C. Melnychuk and Carl J. Walters of the University of British Columbia Fisheries Center, Aswea D. Porter of Kintama Research in Nanaimo, British Columbia, Schreck, Shaun Clements and Benjamin J. Clemens of the U.S. Geological Survey and OSU and R. Scott McKinley of the Centre for Aquaculture and the Environment, University of British Columbia.

Funding for the study was provided by the Census of Marine Life, the Gordon and Betty Moore Foundation, the Bonneville Power Administration, the Northwest Power Planning and Conservation Council, and the U.S. Army Corps of Engineers.

Comparing smolt survival from one river system to another is complex, because there can be a huge difference in the overall "quality" of smolts – even before they begin their long journey to the Pacific Ocean, according to Clements, who conducted some of the tagging studies.

Clements, a former senior research associate at OSU, said the health and fitness of the smolts that are captured at Lower Granite varies significantly.

"One day, we'd get a group of fish that were released from one hatchery and they'd be relatively weak, then a few days later we'd get a bunch of fish from a different hatchery and they would be robust," Clements said. "Hatcheries weren't the only variable -- sometimes fish from the same hatchery would range from poor to excellent in quality, possibly due to environmental factors such as water temperature in the reservoirs. These same mechanisms may also apply to wild fish where we see different watersheds producing smolts of differing quality.

"The point is that the quality of smolts entering into the system can have an impact on their ability to survive the entire migration -- and the transition into the ocean," Clements added. "We don't really have a good understanding of the link between fish quality, hydro system operations and delayed mortality."

The study used a variety of methods to evaluate survival. In the impounded reach of the Columbia River, the researchers used Passive Integrated Technology tag data to evaluate survival between the upper and lower most dams. Tens of thousands of smolts in the upper river are routinely implanted with PIT tags by a number of resource agencies and the data is available online.

Below Bonneville Dam and in the Fraser River they had to use acoustic tags, which are bigger, to pick up a signal from greater distance. The researchers tagged between 300 and 600 fish annually during a four-year period. A first step was an evaluation of the effects the tags themselves might have on fish survival. The acoustic tags are much larger that the PIT tags.

"We first compared survival of PIT and acoustically tagged smolts in the impounded section of the Snake and Columbia rivers to assess survival of animals implanted with these different-sized tags in 2006," according to study results. "Survival of acoustically tagged Snake River spring Chinook smolts from the Dworshak Hatchery stock (tagged and released at Kooskia Hatchery) was statistically indistinguishable from the estimated survival of PIT-tagged Dworshak Hatchery Chinook in 2006 (p > 0.05), demonstrating that the PIT and acoustic tag methodologies provide similar survival estimates for freely migrating smolts in the impounded section of the river."

The studies in the Fraser River and the Columbia River determined that the survival rate of the smolts -- at least to the estuary – was almost identical. Both Clements and Schreck have been involved with other studies, on Oregon's Nehalem and Alsea rivers, that also found a general mortality rate of about 60 percent. In rivers without dams, mortality can be a function of predation -- especially by fish, birds and seals -- or it can be from disease, poor water quality, or lack of food.

"One question that this study raises is: Is significant mortality during in-river migration natural? And if so, what proportion of the fish that are killed by dams in the Columbia -- directly or indirectly -- would have died anyway," Clements said.

Judging historic survival rates of smolts is practically impossible, according to Schreck. Though there is good historical data on returns of adult salmon to river systems, it is difficult to estimate how many smolts they produced and how many young salmon survived their migration to the ocean. Judging what is a healthy survival rate – in historic terms – is a challenge.

Schreck did say that new fish passage technologies and increased release of water over spillways has improved smolts' initial survival of the eight dams on the Columbia River. But there also is evidence that smolts delay their migration for days before trying to navigate past the first dam, which combined with lower river flow rates because of the dams, leads to a delay in entering the ocean.

"We can't emphasize enough how complex salmon survival is," Schreck said. "It begins with the adults returning from the ocean loaded with contaminants, some of which is passed on through the eggs. There can be an impact on the embryo development and transition to the smolt phase. Parasites and disease play a role, as do water quality and other factors.

"Navigating dams may have become easier," he added, "but the process could still be inducing enough stress to cause higher mortality upon reaching the ocean."