[7] Pit-Tag Results Puncture Conventional Wisdom Of Dam Effects On Returning Salmon

Researchers in the Columbia Basin who have been analyzing adult fish survival through the hydro system say it is even better than they previously thought. By keeping track of pit-tagged fish between mainstem dams on the Columbia and Snake rivers, they have found that spring fish losses only amount to two or three percent over the eight-dam route between the lower river and Idaho, according to NOAA Fisheries spokesman Ritchie Graves, who presented the information at this month's meeting of the Northwest Power and Conservation Council in Boise.

Using data gleaned from radio-tagged fish, federal scientists had estimated per-project survival for spring chinook at around 98 percent in the 2004 BiOp, but the new information shows 98-percent survival or better for the four-dam stretch between Bonneville and McNary in the past couple of years, and about the same from McNary through Lower Granite on the Snake.

The earlier data derived from radio tags showed about 13 percent less overall survival for spring and fall chinook.

The latest survival results for summer and fall chinook were about 98 percent for each four-dam stretch of the river. Wild steelhead average about 88 percent survival between Bonneville and McNary and 94 percent between McNary and Lower Granite. Hatchery steelhead fared even better.

On the Upper Columbia the news was good as well. Hatchery steelhead averaged 94 percent survival for the eight-dam route from Bonneville to Wells Dam. That's almost 99-percent survival per project. Hatchery spring chinook averaged about 93-percent survival to Wells Dam. No results were available for wild fish.

The latest adult survival-rate information doesn't jibe very well with the conventional wisdom of fish managers who develop harvest rates for treaty and non-treaty fishers in the Columbia and Snake. According to their 2006 annual report on spring chinook, the managers had estimated overall 2005 survival between Bonneville dam and Lower Granite at only about 70 percent, while the new pit-tag results estimated better than a 98-percent survival. In the past 10 years, the fish managers had pegged loss rates up to 55 percent. WDFW biologist Cindy LeFleur said they are aware of major discrepancies between the newer data and her technical committee's results. "We're going to be looking into that," she told NW Fishletter last week. -B. R.

Subscriptions and Feedback
Subscribe to the Fishletter notification e-mail list.
Send e-mail comments to the editor.

THE ARCHIVE :: Previous NW Fishletter issues and supporting documents.

NW Fishletter is produced by Energy NewsData.
Publisher: Cyrus Noë, Editor: Bill Rudolph
Phone: (206) 285-4848 Fax: (206) 281-8035