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Cooler Weather Helps Record Breaking Fall Chinook Numbers Cross Lower Granite Dam
Posted on Friday, September 27, 2013 (PST)

Southeast Washington and much of the inland Northwest has sweated through a hotter than normal summer season and has been, until very recently, perspiring about the fate of the Snake River fall chinook salmon run.

But those fears have in most regards been washed away. The weather has cooled and rains swept in.

And the counts of fall chinook at lower Snake’s Lower Granite Dam, many of them wild fish listed under the Endangered Species Act, have surged past the record for the fall season.

The total adult fall chinook count climbed to 42,276 Wednesday to surpass the previous record of 41,815 set in 2010. That record dates back to 1975, the year dam operations, and counts, began.

And another 1,854 adult fall chinook passed the counters Thursday to bring the total to 44,130.

The Nez Perce Tribe, responsible for much of the hatchery and habitat restoration work that has helped swell the return, now predicts that Lower Granite adult fall chinook will exceed 50,000.

Approximately 29 percent of the adult fall chinook observed passing Lower Granite so have been adipose fin clipped, meaning they are of hatchery origin.

Because roughly half of the hatchery fall chinook releases in the Snake River are clipped, the low observed clip rate suggests that there are good numbers of natural origin Snake River fall chinook in the return, according to the Columbia River Inter-Tribal Fish Commission’s Stuart Ellis.

Some of the returning fish are unmarked hatchery fish released as part of the tribe’s hatchery supplementation program. Returns of their progeny would ultimately be considered wild fish.

The actual number of “wild,” protected Snake River fall chinook in the return will be estimated at season’s end through the genetic analysis, spawning ground surveys and other work as federal, state and tribal biologists conduct the annual “run reconstruction.”

The cumulative adult fall chinook counts downstream at Little Goose and Lower Monumental dams are also record high counts to date since the construction of the four lower Snake River dams. Lower Granite is the eighth and final dam in the Columbia-Snake system that the fish pass on their way to hatcheries and spawning grounds in the lower Snake basin.

A big return was expected. The preseason forecast was for a return of 31,600 wild Snake River fish to the mouth of the Columbia, which would be 272 percent of the 2003-2012 average, and the highest return on record.

Last year’s wild return was 16,800. Those numbers get trimmed as the fish swim nearly 500 miles upstream through eight dams and a variety of tribal and non-tribal fisheries.

A big overall return was foretold. The Lower Granite count last year of jacks was 21,990, the second highest on record. Jacks are young male fish that return after only one year in the ocean. The jack return helps predict future years’ returns of their broodmates.

The majority of each year’s spawners, classified as adults, have spent two or more years growing and maturing in the ocean. The 2010 record return was preceded by the all-time high jack return of 41,249 in 2009.

This season’s jack count through Thursday is 14,735. Daily counts seemed to have passed the season peak but still strong with a tally of 602 Thursday.

High water temperatures in the dam’s fish ladders in late August and early September appeared to be stalling passage of fall chinook headed upstream to spawn. Early September fish ladder counts dipped at a time when typically the run would be surging toward a peak.

A similar happening for the rebuilding sockeye salmon run in late July forced a variety of operational changes at Lower Granite in an attempt to improve fish ladder conditions.

Operational changes were implemented earlier this month by the U.S. Army Corps of Engineers intended to improve water temperature conditions, and a timely change in the weather helped. Cooling air temperatures and rains boosted daily counts to record levels last week.

Improved conditions also allowed the startup Monday of the adult fish trap in the fishway, which is used to collect broodstock for both the Lyons Ferry Hatchery and the Nez Perce Tribal Hatchery and to handle fish for a variety of research purposes such as collecting scale samples for genetic analysis and inserting and reading PIT and radio tags.

“This is the latest we’ve been shut down, and the longest we’ve been shut down,” said Darren Ogden, the NOAA Fisheries research fish biologist in charge of running trap operations. The trap had been out of commission since July 10.

“Typically we start in March and we don’t stop unless we have temperature problems or mechanical problems,” Ogden said.

“It’s nerve wracking,” Becky Johnson, head of the NPT’s Production Division, said of the trap closure, and the need to collect about 5,000 fish as broodstock to produce the next generation of fish at the hatchery.

The restarted operation of the fish trap would seem to be in the nick of time. Ogden said that just over 1,000 fall chinook were collected Monday and Tuesday.

The fish ladder temperature issues seem to emerge only occasionally, in extreme years.

“That’s something that needs to be fixed,” Johnson said of the Corps’ ability to draw cooler water from the depths of Lower Granite’s reservoir to feed the fish ladder.

NOAA Fisheries’ 2008 biological opinion for the Federal Columbia River Power System calls for an investigation of the situation at Lower Granite Dam and, if necessary, the provision of “additional auxiliary water supply for the new adult trap at lower Granite” so that it can operate at full capacity when the forebay is operated at minimum operating without affecting the fishway. NOAA Fisheries BiOps suggest actions necessary to avoid jeopardizing the survival of ESA listed stocks, such as the Snake River sockeye and fall chinook.

For more on the “thermal barrier” see CBB, August 2, 2013, “Endangered Adult Sockeye Passing Little Goose Dam Then Hitting Lower Granite’s ‘Thermal Barrier’’

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