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Researchers Say Ocean Holds Hope for 2001 Outmigrants

by Barry Espenson
Columbia Basin Bulletin - February 8, 2002

Migrating juvenile spring chinook salmon and steelhead faced a gauntlet last year with low, clear, and often warmer, Columbia-Snake river flows retarding their downstream progress and leaving them more readily accessible to fish and avian predators, according to National Marine Fisheries Service officials.

The steelhead that swam down river through the basin's hydrosystem suffered the highest mortality yet recorded in an ongoing National Marine Fisheries study that began in 1993. Only an estimated 4 percent made it the length of the lower Snake-Columbia hydrosystem from Lower Granite to Bonneville Dam. The spring chinook estimate was higher at 27.6 percent survival, but was substantially lower than the 43 to 59 percent survivals of the previous six years.

The future of that year's brood rests with the substantial numbers of young fish that were collected and barged through the hydrosystem.

"I guess we don't know what it will mean in terms of adult returns, but it may not be as bad as some people predicted," John Muir, a NMFS fisheries research biologist, said of the long-term effects of last year's drought on that year class of salmon.

Muir and fellow NMFS researchers Steve Smith and John Williams on Wednesday offered summaries of their 2001 chinook salmon and steelhead survival through specific river reaches and through the entire system. The presentation to the Northwest Power Planning Council, and a draft report produced at year's end, also theorize about the effects of near-record low Columbia Basin flows and of limited hydrosystem spill on spring migrants' survival.

The scientists also offered views on fall chinook salmon survival, and on the effect 2001's events may have on future adults chinook and steelhead returns.

The draft report updates a NMFS-University of Washington study through its ninth year. The goal is to estimate survival and travel times for juvenile salmonids passing through dams and reservoirs on the Snake and Columbia rivers. The various study release groups are monitored as they pass downstream via passive integrated transponder (PIT) tags implanted in the fish. The tags are detected at Lower Granite, Little Goose and Lower Monumental dams on the lower snake River and at McNary, John Day and Bonneville dams on the Columbia, as well as at a trawl operated in the Columbia estuary.

The federal agency estimates that 98 percent of the Snake River spring chinook and steelhead juveniles from the 2001 spring migration that made it past Bonneville Dam alive were transported. Bonneville Dam is the last hydro project on the mainstem before the Columbia River empties into the Pacific Ocean. Muir told the NWPPC that the average transported during the previous years of the study had been 87 percent for chinook and 93 percent for steelhead.

The low river flows during 2001's drought forced a "power emergency" declaration by the Bonneville Power Administration that resulted in limited spill as federal dams to provide fish passage. As a result, juvenile salmon collection facilities were more efficient.

"Thus, the consequences of the low-flow conditions in 2001 on Snake River stocks will depend almost entirely on the adult return rate for the transported fish," according to draft NMFS survival estimates. Collection facilities exist at Lower Granite, Little Goose and lower Monumental dams and at McNary. Roughly three-quarters of the fish used in the releases at or above Lower Granite were hatchery fish with the balance being wild fish.

Ocean conditions could well settle the fate of this year's spring chinook and steelhead year class, Muir said. Ocean upwelling that has flushed out nutrients and resulted in cooler water through many of the Columbia Basin stocks' ocean range are credited with enhancing survival -- and the adult returns to the river. Record (since counts began in 1938) upriver spring chinook and summer steelhead returns were realized last year.

High counts are anticipated this year as well. Continued good ocean conditions could well muffle the effects of 2001's freshwater drought, Muir said, since resulting improved returns don't seem to play favorites.

"They are all showing the same pattern" of improvement, Muir said of hatchery and wild fish, and returns from juveniles that were transported or migrated in-river. The wild card is the ocean.

"We don't know that they're favorable, but we think they're favorable," Muir said assessments of a continuation of recent years' favorable conditions. Changing ocean conditions are hard to forecast.

"It's an extremely dynamic place," Muir said.

The Fish Passage Center's Margaret Filardo said that she too was hopeful that the drought's effects on the 2001 outmigrants could be counterbalance by improved ocean survival -- though her enthusiasm was qualified.

"There's so many things that you've got to line up before you get to the ocean," Filardo said of the migrants' final gauntlet through more than 100 miles of the lower river and through the estuary. FPC survival estimates to points just below Bonneville are similar to those compiled by NMFS, she said.

Those fish that stayed in-river faced many perils. With only limited spill, many fish faced turbine passage. They also swam through low, slow-moving waters that slowed migration times for early season migrants by as many as 20 to 30 days, Muir said.

"Flow levels during the 2001 spring migration period were the lowest recorded during the nine years of this study," according to the draft report. "Springtime spill was also very limited in 2001. Estimated survival from Lower Granite Dam to the tailrace of Bonneville Dam was the lowest recorded in the past nine years for spring chinook and steelhead."

An especially perilous stretch was between Lower Monumental and McNary (which includes Ice Harbor passage) where only 29 percent of the tagged steelhead are estimated to have survived.

Among the hazards was a Caspian tern colony holding an estimated 800 nesting pairs on Crescent Island. More than 5,000 PIT tags from steelhead tagged in 2001 were recovered on Crescent Island. Preliminary analyses indicates that at least 14 percent of the steelhead detected on Lower Monumental were preyed on by the terns.

Barry Espenson
Researchers Say Ocean Holds Hope for 2001 Outmigrants
Columbia Basin Bulletin, February 8, 2002

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