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Snake Fall Chinook Run Poised for
Best Wild Return since 1960's

by Bill Rudolph
NW Fishletter, September 19, 2013

Graphic: Lower Granite fish counts of adult Chinook salmon.  Cooler water temperatures have made to erase the thermal barrier at Lower Granite Dam up the Snake River. The record run of upriver brights in the Columbia River has overshadowed another potential record--the fall run in the Snake looks like it will easily eclipse 2010's record of nearly 42,000 hatchery and wild fish counted at Lower Granite Dam, the largest run in many decades.

With more than 33,000 adult fall Chinook already counted at Ice Harbor Dam--the lowest of the four dams on the Lower Snake, there is still a solid month of returns to look forward to. Low flows and warm water has been keeping fish from making a speedy migration, and dam operators have experimented with several ways to attract them towards the fish ladder. With flows below 20 kcfs, it was obvious from dam counts that fish have been backing up at several projects.

But now the weather is cooling off and passage problems seemed to have eased further upriver at Lower Granite--nearly 3,500 adults passed the dam on Sept. 17, seven times the previous day's number, with a 20,000-fish total.

WDFW biologist Glen Mendel, who works at the agency's Dayton, Wash. office, and has been in the business of restoring the fall run for many years, said he thinks this year's return will crack the old record--maybe even back to the 1960's, when the only dam on the lower Snake was at Ice Harbor. Before Ice went in, few accurate records were available for returns to the Snake, but runs were all wild fish then, heading up to Hells Canyon and beyond to spawn in a large area later blocked by Idaho Power's 3-dam complex, completed in 1967.

By 1975, when the Lower Granite project was finished (the last of four dams on the lower Snake), the fall run had dwindled down to 78 fish. Since then, passage improvements, a large supplementation effort, and good ocean conditions have all helped to rebuild the run, despite an overall harvest rate that's still above 40 percent, most of it in the Columbia.

This year's return of natural-origin fish will likely beat 1963's total, when nearly 14,000 fall Chinook were counted at Ice Harbor, then, the only dam on the lower Snake. Nearly that many natural-origin fish returned in 2012, according to information released last month at the annual meeting of biologists and fish managers who work on the Snake supplementation effort.

The managers also reported they have been recalculating natural-origin fall Chinook returns back to 2005, but that's where they have to stop, said WDFW biologist Debbie Milks, because of methodology changes in counting that year. However, it was reported at that meeting natural-origin returns have achieved a 10-year geomean of 6,342 fish--which means the adult return has been above NMFS' interim recovery goal each year for the last decade.

But don't expect the fall run will be delisted anytime soon. USFWS biologist Billy Connor, who has worked on Snake fall Chinook issue for much of his career, said managers are wrestling with those recovery questions right now, as they complete the recovery plan for the fish. Connor said one of the big questions is what will happen to returns if the large supplementation effort is dialed back. NMFS biologists are very concerned about the large number of hatchery fish on the spawning grounds below Halls Canyon. They figure that most natural spawners in recent years have had at least one hatchery-origin parent from a common broodstock.

Connor also noted that the fall Chinook run is nothing like the original Snake run that spawned all the way to Nevada. In 1901, with the construction of the Swan Falls Dam, near Boise, more than 240 river kilometers of spawning habitat was forever lost. In those days, lower Columbia harvesters caught one to two million fish every year. Gold dredging and logging further decimated fish habitat. Some estimates for the period 1915-1919 put 1.25 million Chinook at the Columbia mouth and 460,000 for the Snake. By the late 1940's, fall Chinook escapement in the Snake had declined to about 20,000 fish on average.

The rebounding fall run is now supplemented by fish from the Clearwater, were cold water temperatures keep many juveniles from migrating until the following spring--creating a yearling component to the migration that wasn't there before. The new fall run is a product of the several technical fixes and has adapted to man's tinkering with the river and attempts at boosting fish numbers, Connor emphasized, which means the run that will be recovered is a lot different from the returns of 50 years ago.

A presentation by NOAA fisheries biologist Tom Cooney at the August meeting outlined what scientists know and what the still need to know before the fish may be officially delisted.

By 2017, he said managers will have a good understanding of total escapement upstream of Lower Granite Dam, the abundance of natural-origin and hatchery returns, the percentage of the hatchery-origin fish in the naturally spawning population, and the percentage of the natural-origin fish used in hatchery broodstocks, with genetic diversity and effective population size of natural and hatchery-origin population segments.

By 2017, he said, managers may have an improved understanding of the productivity of the naturally spawning population, the percentage of the hatchery-origin fish in the naturally spawning population at spawning aggregate scales, the relative magnitude juvenile production from some spawning aggregates, and density dependent relationships between spawner abundance and juvenile production.

But by 2017, managers still won't be able to understand the relative reproductive success of hatchery and natural-origin spawners, along with the differential use of habitats by hatchery and natural-origin fish, the abundance of basin-wide juvenile production, the impact of sturgeon and birds on juvenile production, or understand the ecological processes supported (or hindered) by an abundance (or scarcity) of natural spawners.

Bill Rudolph
Snake Fall Chinook Run Poised for Best Wild Return since 1960's
NW Fishletter, September 19, 2013

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