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Juvenile Steelhead Survival Down This Year

by Bill Rudolph
NW Fishletter, November 7, 2013

Graphic: In-River survival of juvenile Chinook and Steelhead through Snake and Columbia Rivers (Lower Granite tailrace to Bonneville tailrace NOAA Fisheries researchers announced preliminary results last week for juvenile PIT tagged fish survival through the hydro system in 2013. For yearling Chinook, survival from the tailrace of Lower Granite Dam on the Snake River to the tailrace of Bonneville Dam amounted to nearly 62 percent, the third highest in the 1999-2013 time frame.

(bluefish notes: For comparison with graphic (Snake River Trap to Bonneville Dam tailrace), one needs to consider the mortality associated with juvenile passage through Lower Granite Dam and reservoir.)

But for steelhead, the 50.1-percent survival rate was the lowest seen since 2008, and down nearly 10 percent from 2012. The annual survival memo from NOAA noted that survival for young steelhead was below average in 2013 from McNary to John Day dams, and from Lower Monumental Dam to McNary.

Upper Columbia hatchery spring Chinook showed a 100-percent survival rate from the McNary tailrace to the Bonneville tailrace, while upper-C hatchery steelhead estimated survival from McNary to Bonneville was 93.2 percent. Survival from mid-Columbia dams can't be estimated due to limited PIT-tag detection systems.

For Snake River sockeye (hatchery and wild), the Lower Granite to Bonneville survival rate was 53.6 percent, up 5 percent over 2012 survivals, and well above the long-term mean of 40.6 percent. About 48.7 percent of the Upper-C sockeye made it from Rock Island Dam to Bonneville, down significantly from the nearly 80-percent survival rate last year, and below the long-term mean of nearly 54 percent.

NOAA estimated that only 36.1 percent of the wild yearling Chinook smolts and 31 percent of hatchery smolts from the Snake were transported this year, while 40 percent of wild steelhead and 35 percent of hatchery steelhead were transported.

The memo also noted that mean spring flow on the Snake at Little Goose Dam was only about 68 kcfs, well below the long-term mean of 92.0 kcfs, which put it at the fifth lowest level over the past 21 years.

Mean spill volume at lower Snake dams was 22.3 kcfs, a little below the long-term average of 25.9 kcfs. Daily spill volumes were average except for a period from May 15 to June 15.

Spill percentage at the lower Snake dams was 33.5 percent in 2013, above the long-term average of 25.1 percent, and was above average every day expect for the May 9-15 period when there was a period of increased flow.

The memo said overall river conditions were similar to 2007 and 2010 -- "low flows with moderately high temperatures at times and with above-average spill percentages." A higher percentage of fish were barged this year than the record lows of 2012, because barging began a few days earlier at Lower Granite and most smolts arrived later at the dam than in 2012.

High spill percentages and continuous operation of the surface collectors resulted in low percentages of fish that entered bypass systems necessary for routing to barges. "Low flow conditions in 2013 may have increased spillway passage because lower water velocities allow fish more time to react to conditions and may increase the attractiveness of surface bypass collectors," said the memo, which noted that about 46 percent of the Chinook and 51 percent of the steelhead arriving at Lower Granite were barged from one of the collector dams during the period of general transportation.

That is actually lower than 2012 percentages of 59 percent for Chinook and 62 percent for steelhead, said the memo. "Despite the increase over 2012 estimates, the transport percentages for 2013 are still among the lowest estimated over the period for which we have estimates (1993-2013)." Only about 25 percent of the migrating Chinook and steelhead (hatchery and wild) were transported in 2012.

Bill Rudolph
Juvenile Steelhead Survival Down This Year
NW Fishletter, November 7, 2013

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