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Latest Data Shows Barging Fish Still Best for Most Snake Stocks by Bill Rudolph NW Fishletter, January 13, 2013

Most hatchery spring/summer Chinook smolts barged from the lower Snake River dams show higher SARs [smolt-to-adult return rate] than fish allowed to migrate inriver, according to some late December 2012 memos from the Fish Passage Center to regional hatchery managers updating the FPC's ongoing PIT-tag survival study.

The latest results tracked the 2010 outmigration, when NOAA estimated about 57 percent of the inriver migrating Snake spring Chinook (hatchery and wild) made it safely from Lower Granite Dam to below Bonneville Dam, 5 percent better than the 1999-2010 average, and close to 2009's 56-percent return rate. It was also better than 2008's 47-percent rate, due to good flow and high spill, and nearly the same as the 60-percent rate in 2007, another low-flow/high-spill year.

With adult returns through 2012, the late-December FPC memos reported barging benefits for Snake River hatchery spring Chinook compared to inriver migrants that ranged from 28 percent for Rapid River summer Chinook to 45 percent for Sawtooth Hatchery spring Chinook.

Unfortunately, the high spill levels meant fewer smolts were captured for barging in 2010 than usual. Only 14 percent of the PIT-tagged spring Chinook from the Clearwater Hatchery were barged, compared to 34 percent in 2009. The highest percentage barged were smolts from the Catherine Creek acclimation facility (29 percent) and the McCall Hatchery (28 percent).

Overall SARs for both hatchery and inriver migrants were down considerably compared to returns from the 2008 outmigration, when smolts entered the ocean during primo La Nina conditions. For McCall summer Chinook, the SAR for the 2010 outmigration averaged about .53 percent, about half the SAR from the 2007 and 2008 outmigrations. The overall Sawtooth Hatchery spring Chinook SAR was about .42 percent, compared to the 1.00 percent return from the 2008 outmigration.

Dworshak Hatchery spring Chinook returns showed that 2010 inriver migrating fish actually did 30 percent better than the transports, while transported Clearwater Hatchery springers had a 30-percent advantage over inrivers. The overall SAR for each group was slightly under 0.5 percent.

Results for wild Snake Chinook as reported in the FPC's final CSS report released Nov. 30, showed that transported wild Chinook did slightly better than inriver migrating fish from the 2010 migration year, with a 1.08 percent SAR compared to a 1.05 percent SAR for inrivers (Note: The FPC results compare transported PIT-tagged smolts with returns of smolts never detected at the collector dams; the smolt numbers of never-detected fish that pass over spillways or through turbines are estimated).

Some survival results from several Upper Columbia hatchery stocks were also reported. Leavenworth spring Chinook that migrated in 2010 showed an overall SAR (McNary-Bonn) of 0.75 percent, better than 2009's 0.57 percent but less than half of the 2008 SAR of 1.91 percent.

Subyearling and yearling fall Chinook released from the Wells Hatchery in May 2012 showed about a 25-percent survival rate to McNary Dam, about half of 2011's survival rate.

From release to McNary, Priest Rapids Hatchery fall Chinook survival was significantly lower in 2012 than the previous year, and the lowest since 1997. The FPC estimated about 50 percent made it to the dam, while 82 percent made it in 2011.

Further downriver, the spring Chinook releases from the Carson Hatchery in 2010 resulted in an overall SAR of .72 percent (release back to Bonneville), about half the return rate from the 2008 and 2009 outmigrations.