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Steelhead Crossing Bonneville Dam in Record Numbers

Environmental News Network - August 24, 2001

Adult salmon climbs a fish ladder to bypass the Bonneville Dam. Salmon and steelhead runs have been declining all along the west coast for decades, but this year there is good news from Idaho. The largest steelhead run in the history of dam counts is crossing Bonneville Dam on its way up the Columbia River. As of August 19, the count of steelhead at Bonneville topped 390,000, Idaho fisheries officials report.

Most of these steelhead are of hatchery origin, however, not the wild runs that came upriver before the Bonneville Dam was built in 1938.

Steelhead trout, the sea-run form of rainbow trout, are considered to be a variety of salmon, a salmonid. They are listed by the federal government as threatened or endangered all along the coast of California, and in the interior rivers and streams of Oregon, Washington, and Idaho.

Many salmon and steelhead populations in the Columbia River Basin will be extinct or nearly so by the end of this century, unless the region makes major changes to improve their survival, warned a federal status report last year. The human activities that have caused the decline of these fish are habitat, harvest, hatcheries, and hydropower.

Salmon are hardy, traveling hundreds or thousands of miles from river to ocean and back. But they need specific habitat conditions to thrive -- sufficient flows of cool, clean water, gravel beds free of sediment where they can spawn, a healthy nutrient base, and passable migration corridors.

This season, salmon returns on the Columbia River are encouraging. Coming over Bonneville Dam, the first dam steelhead must negotiate on the Columbia, the Aug. 12 count was nearly four times the 1991 to 2000 average of 96,000 steelhead.

The current forecast for Bonneville calls for at least 500,000 steelhead. Last year, 274,000 steelhead crossed Bonneville.

If water temperatures remain near normal in the Snake River, it is likely this steelhead run could set a record for numbers entering Idaho, state fish and game officials say.

Water temperature has been a serious concern because of drought and hot weather conditions in Idaho this summer. Steelhead passage over Lower Granite Dam came to a virtual standstill earlier this summer as water in the forebay of the dam heated up to almost 77 degrees. Temperatures have since gone down in the Snake River system.

Temperatures have declined in the Snake in the last few days, improving the rate of steelhead crossing at Lower Granite Dam. As the water temperature fell from 76.6 degrees to about 70 degrees, steelhead started moving into Idaho again.

It is not uncommon for a thermal block to develop in the lower Columbia river or between the Columbia and Snake Rivers where the Snake is often warmer than the Columbia. The warmer water can keep steelhead from entering the Snake River. In other years of low, warm water thousands of Idaho steelhead never made it home.

Barrett says steelhead migrating up the Salmon and Snake rivers seem to be attracted to the cooler water of the lower Clearwater River, and will stay there temporarily before swimming to their final destination.

The mature fish have to negotiate the Lower Columbia River, in Washington state, on their way from the sea up the river into Idaho where they will spawn and die. Then the juveniles they have spawned later swim out to sea by the same river route.

Washington's portion of the Lower Columbia's so-called Evolutionarily Significant Units contains 12 wild winter steelhead stocks and five wild summer steelhead stocks. Most are classified as "depressed" by a 1998 report from the Washington Governor's Salmon Recovery Office.

Juvenile wild steelhead usually rear in freshwater for one to three years before undergoing a physiological change to become smolts and outmigrating to sea. Wild steelhead smolts migrate from freshwater to saltwater from March through June.

Hatchery steelhead are typically reared for one year prior to release as smolts in April or May.

Juvenile steelhead tend to move offshore soon after entering the ocean, where they move north-westward from the mouth of the Columbia River. By July, most juvenile steelhead can be found offshore in the Gulf of Alaska, and the ocean conditions they encounter affect their rate of return to the rivers of their birth, to spawn and die in their turn.

In 1999, Washington state put in place its Statewide Strategy to Recover Salmon, specifically addressing ecosystem health and the conservation measures that must be taken to recover wild steelhead stocks. Habitat enhancement measures, harvest and hatchery management practices have been put in place, and Washington state is opposing all proposals for new hydroelectric projects with the potential for degrading salmon habitat.

Some of the conservation measures taken as part of this strategy may be responsible for the increased steelhead run crossing the Bonneville Dam right now.

by ENN
Steelhead Crossing Bonneville Dam in Record Numbers
Environmental News Network - August 24, 2001

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