Imperiled Steelhead Migrating Up Columbia/Snake River Show Lowest Survival Bonneville Dam To McNary Dam, Miss Survival Targets

Asotin Creek adult summer steelhead survival is at its lowest in the Bonneville Dam pool as the fish migrate upstream to the Snake River tributary, according to a presentation last week that focused on survival of steelhead listed as threatened under the federal Endangered Species Act. Temperature and harvest (catch and release mortalities) are cited as the main reasons for steelhead struggles in the Bonneville Pool.

The good news is that survival of adult steelhead improves the farther upriver they migrate. Survival in the next three reservoirs – The Dalles, John Day and McNary pools – is higher, in some years as high as 95 percent, Dan Rawding, Columbia River Science and Policy Coordinator with the Washington Department of Fish and Wildlife told the Fish and Wildlife Committee of the Northwest Power and Conservation Council.

And, when these fish have migrated into the lower Snake River at Lower Granite Dam, survival rises to a consistent 97 and 98 percent range, he said. Still, Rawding said in his presentation, Asotin Creek summer steelhead are not meeting their survival target between Bonneville and McNary dams.

Rawding spoke to the Fish and Wildlife Committee at its meeting in Olympia, April 9, in a shared presentation with Andrew Murdoch, Eastern Washington Science Division Manager with WDFW. Murdoch also presented survival estimates of steelhead, but for upper Columbia River steelhead as they migrate to their natal streams, including survival of steelhead that overshoot their natal stream, pass one or more dams and migrate back downstream to return their spawning grounds.

Upper Columbia and the Snake River steelhead are both listed under the federal ESA as threatened.

In the lower Columbia, survival of Snake River summer steelhead is generally lower than what is called for in the Council’s 2020 Addendum to the 2014 Columbia River Basin Fish and Wildlife Program, which includes a biological objective to achieve annual adult salmon and steelhead survival standards through the Bonneville Dam to Lower Granite Dam reach and the Bonneville Dam to McNary Dam reach, an April 2 Council Memorandum says (https://www.nwcouncil.org/fs/18689/2024_04_f4.pdf).

For Snake River steelhead migrating from Bonneville to McNary Dam, the survival standard is 90.1 percent, yet current survival in the Bonneville pool itself is lower at about 80 percent (2007-2021).

Survival from McNary to Lower Granite Dam on the lower Snake River is about 90 percent, but survival over the longer reach from Bonneville to Lower Granite Dam is only about 70 percent.

“We lose about 30 percent of the fish through the basin,” Rawding said of the Asotin Creek summer steelhead. Asotin Creek in southeast Washington flows into the Snake River just upstream of Lower Granite Dam.

Snake River summer steelhead migrate past Bonneville Dam as water in the Columbia River is heating up, June through September, Rawding said. They spawn in their natal river the following year, March through May.

The Snake River steelhead Distinct population segments include all naturally spawned steelhead in the basin. DPS populations are found in the lower Snake, Grande Ronde, Imnaha, Clearwater, Salmon rivers and Hells Canyon Tributaries.

“A good example of the conditions encountered by Snake River steelhead is the Tucannon River and Asotin Creek populations where NOAA expressed concerns about the lack of stream complexity, excess sediment, low stream flows, high stream temperatures, degraded riparian conditions, reduced floodplain connectivity, and specific to the Tucannon – passage barriers,” the Council memo says.

The survival standard for Upper Columbia River steelhead migrating from Bonneville Dam to McNary Dam is 84.5 percent, the memo says. Lower Columbia River steelhead do not have an adult performance standard, it is assumed survival is adequate if Snake River steelhead standards are met. Upper Willamette River steelhead have no adult performance standard, either.

Sometimes steelhead, especially those that migrate into the mid- or upper-Columbia River, will travel beyond their natal spawning stream and even go upriver past dams. These fish are “overshooting” their natal stream and many may not return downstream to spawn. Depending on how many dams they overshoot, it could impact their ability to get back to their natal stream, Murdoch said.

Overshooting is not the same as straying, he said. Overshooting refers to a fish that migrates upstream of its natal tributary over at least one dam. Some or many of these fish will then again migrate or “fall back” downstream of the dam. A straying fish is one that is of non-local origin that spawns in a non-local stream. Up to 13 percent of steelhead migrants will stray.

Over 33 percent of John Day River steelhead in the mid-Columbia River will continue on to Ice Harbor Dam on the lower Snake River, and as much as 5 percent of John Day fish will overshoot to Priest Rapids Dam on the upper Columbia.

A similar proportion of Walla Walla River steelhead will also overshoot and, instead, at least initially, head upstream. Some 30 percent will pass Ice Harbor, while an additional 3 percent will pass Priest Rapids.

Some 19 percent of Umatilla River steelhead will overshoot the river, with about 17 percent passing Ice Harbor and 2 percent passing Priest Rapids.

About 14 percent of Yakima River steelhead will overshoot, with roughly equal proportions going to Priest Rapids and Ice Harbor.

The fallback migration success for these wild steelhead – they overshoot their natal stream and pass Priest Rapids Dam and then fallback to their natal stream – varies by year, but the mean (2010 to 2017) is 59 percent of the overshooting fish. Migration success during these years has been as low as 31 percent for brood year 2016 and as high as 74 percent for brood year 2014.

However, some 4 to 17 percent of Yakima River wild steelhead do not return to the river (they are not later detected at Prosser Dam on the river). The mean is 7 percent over the years 2010 to 2021. Murdoch said that the 17 percent that do not return to the river is “something to be concerned about.”

In general, two out of five wild steelhead detected at Priest Rapids Dam are overshoots, Murdoch said. Of those, two out of five never make it back to their natal river and only a small proportion are detected on spawning grounds.

“Mid-Columbia steelhead,” Murdoch said in his presentation “are impacted the greatest by overshooting.”

Cool water populations tend not to overshoot, Murdoch said. That includes steelhead whose natal streams include the Deschutes River in Oregon and the White Salmon and Klickitat rivers in Washington.

For background, see:

— CBB, October 6, 2022, NOAA FISHERIES FINALIZES ‘REBUILDING’ REPORT TO INFORM DIALOGUE ON COLUMBIA RIVER BASIN SALMON RESTORATION, https://columbiabasinbulletin.org/noaa-fisheries-finalizes-rebuilding-report-to-inform-dialogue-on-columbia-river-basin-salmon-restoration/

— CBB, July 23, 2019, STUDY INVESTIGATES REASONS FOR STRAYING OF HATCHERY FISH IN COASTAL RIVER; LACK OF UNIQUE ODOR CUE CITED, https://columbiabasinbulletin.org/study-investigates-reasons-for-straying-of-hatchery-fish-in-coastal-river-lack-of-unique-odor-cue-cited/