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Research shows adult salmon survival nears 100 percent during upstream migration in Columbia and Snake rivers
June 15, 2006
BOISE —Research shows that the survival of adult salmon and steelhead at and between hydroelectric dams on the Columbia and Snake rivers is averaging 98 percent and better in recent years, a NOAA Fisheries scientist told the Northwest Power and Conservation Council Tuesday at a meeting in Boise.
“That’s real high survival; most people would agree those are good numbers to have,” said Ritchie Graves, acting branch chief of NOAA Fisheries’ regional Hydropower Division in Portland. NOAA Fisheries is the federal agency that implements the Endangered Species Act for salmon and steelhead in the Northwest.
Council Chair Tom Karier said the results are encouraging.
“At least the adult salmon do not appear to have difficulty with the dams,” Karier said. “This is good news if we are only losing 1 or 2 percent of the fish migrating upstream.”
Council Member Judi Danielson of Idaho said the results bode well for salmon and steelhead returning to that state: “We hear so much about the impact of the dams, but here is data that shows we have done so much to improve passage survival through the hydrosystem; now it is time to sharpen our focus on improving fish survival in other areas, particularly harvest, which has been 9 percent or more on these fish between dams.”
NOAA Fisheries’ research relies on detections of PIT (passive intermodal transponder) tags that are inserted in many fish when they migrate to the ocean as juveniles. During that downstream migration, and also when the fish return from the ocean to spawn as adults, the tags can be detected as the fish cross dams. The percentage of adult fish that return to spawn — the survival — is called the conversion rate.
Because the tags identify fish by the location where they were released, tagged fish can be tracked through most of their river migration. Survival at and between the dams is estimated through calculations that adjust the number of detections with sources of mortality — harvest and predation, for example. It’s not precise — some fish elude detection at one dam and are detected at another — but the accuracy of calculating conversion rates is improving as the detection equipment becomes more sophisticated.
Graves presented results for Chinook and steelhead survival between Bonneville and McNary dams, and also for McNary to Wells Dam on the Columbia and McNary to Lower Granite Dam on the Snake. Wild and hatchery-reared spring Chinook released as juveniles above Lower Granite Dam experienced about 99 percent survival between Bonneville and McNary dams when they returned as adults, and 99-100 percent survival between McNary and Lower Granite dams, Graves said. The survival of Snake River summer and fall Chinook between McNary and Lower Granite dams, and for upper Columbia steelhead between McNary and Wells dams, averaged 97-98 percent.
Using PIT tags to estimate conversion rates is faster than the traditional technique of basing survival estimates on detections of fish that carry radio tags — a different type of technology, Graves said. As well, harvest managers could use the same analytical technique to better understand the impacts of fisheries that are targeted to catch — or avoid catching — specific salmon and steelhead runs.
“We’re going to continue to refine this technique,” he said.
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