Improvements at all eight federal Snake and lower Columbia River dams boosted the safe migration of juvenile salmon and steelhead last year, according to a federal study.
Army Corps of Engineers officials said completion of passage improvements such as spillway weirs, also called fish slides, help speed young fish downstream past dams by keeping them near the water surface, where they naturally migrate.
For example, tests at Little Goose Dam on the Snake River found that 99.4 percent of yearling chinook, 99.8 percent of steelhead and 95.2 percent of sub-yearling chinook passed the dam safely.
"Almost all of the fish are coming through the dam safely now and we're on track to meet passage standards at all of the other projects," said Corps official Witt Anderson.
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The assessment report says in-river survival of juvenile Snake River steelhead migrating to the ocean in 2009 reached its highest level in 12 years, a sign the fish are benefiting from improved surface passage.
The report describes the second year of progress by the Corps, U.S. Bureau of Reclamation and Bonneville Power Administration in implementing NOAA-Fisheries' biological opinion for the federal Columbia River power system. The so-called bi-op outlines protections for fish affected by the federal dams.
According to the assessment, the agencies in 2009 reopened nearly 265 miles of spawning and other salmon and steelhead habitat that had been blocked by impassible culverts, diversions or other obstacles. Since 2005 the agencies have restored access to a total of 845 miles of habitat.
"Fish are returning in numbers we haven't seen in decades and to places they haven't been for decades," said Lorri Bodi of the Bonneville Power Administration.
The report also says the agencies in 2009 restored water to salmon and steelhead streams that otherwise dwindle or run dry when fish are returning to spawn.
The 190 cubic feet per second of flow restored to streams in the Columbia River Basin last year exceeds the average amount of water consumed by Portland and nearby cities, and the amount of water restored since 2005 totals more than three times the average water use of Seattle and Portland combined.
The report also says efforts to redistribute a large colony of Caspian terns in the Columbia River estuary helped reduce their predation on juvenile salmon and steelhead from about 15 million fish in 1999 to 6.4 million in 2009.
However, it says double-crested cormorant predation on the fish is a growing concern. Together cormorants and terns ate 17.5 million juvenile salmon and steelhead in 2009, about 15 percent of all those that reached the estuary.