Although NOAA Fisheries’ annual memo on the survival rates of juvenile salmon and steelhead migrating through the Snake and Columbia river dams this year is still preliminary, some members of the Columbia River Technical Management Team (TMT) want to know whether the data will be used to examine the success of the 2019 flexible spill regime or guide future spill operations.
NOAA Fisheries biologist Paul Wagner presented the preliminary survival estimates at TMT’s Sept. 25 meeting, summarizing, “This year wasn’t great, but it wasn’t terrible.”
The agency expects to release final survival rates, and a more detailed analysis, in February or March of 2020. Changes in the database by then could cause final survival rates to differ by up to 4 percent, according to the Sept. 19 memo.
The memo comes after a challenging spring spill season that required the U.S. Army Corps of Engineers to attempt to keep total dissolved gas levels at 120 percent at eight dams for 16 hours a day. One objective of the agreement is to provide additional benefits to fish through spill, by improving juvenile migration conditions.
“We look at this every year, and every year we’re making changes in operations, and the two never seem to marry,” TMT member Jim Litchfield, who represents Montana, said during Wagner’s presentation. “This is really never having to say you’re sorry. We expect to see effects from a new spill operation, and we don’t, but we don’t know what to do about it so we move on."
Fish managers noted many variables in the system could have contributed to lower survival rates for some species in some reaches, compared with long-term survival rates.
But TMT member Claire McGrath, representing NOAA Fisheries, said the timing is good to look into the question of spill operations and how they relate to juvenile survival. She said fish managers were already asking whether this year’s good flow conditions were reflected in travel times. “This memo doesn’t address that, but I think that’s a really good question. I would expect to put some attention toward that in the final report,” she said.
The memo notes the last several years have provided shorter smolt travel time from Lower Granite Dam to Bonneville Dam. “However, 2019 was an exception, especially for yearling Chinook salmon. Under the current spill regime, 2019 joined 2011, 2012, 2017 and 2018 as years we have classified as high-flow,” it said. This April, yearling Chinook travel times were several days longer than in 2017 and 2018. Their travel times decreased in May to levels similar to 2017 and 2018, the preliminary report said. Median travel time for steelhead this year was also slightly longer than 2017 and 2018, it noted, with travel times about one day longer than those from the same week in 2017 and 2018.
Using data from passive integrated transponder tags, NOAA Fisheries has issued reports on migrating juvenile survival rates since 1993. Although preliminary, the memo includes estimates for survival of hatchery and wild fish between specific dams, and for overall survival rates to Bonneville Dam from the traps above Lower Granite Dam on the Snake River, and from McNary or Rock Island dams on the Columbia River.
While the hatchery, wild and reach-by-reach results vary, this year’s total survival rates were generally worse than or similar to the long-term averages, except for sockeye, which were better. When adding in the potential for a 4-percent difference between preliminary and final survival estimates, most results are relatively close to the long-term rates, except for upper Columbia River sockeye, where the estimated survival rate this year is much higher than long-term survival rates.
According to initial estimates, combined hatchery and wild Snake River yearling Chinook from the traps above Lower Granite Dam to Bonneville Dam’s tailrace had a survival rate of 41.3 percent this year, compared to the long-term average of 48.5 percent. Combined hatchery and wild Snake River steelhead had a survival rate of 41.2 percent, compared to the long-term average of 45.7 percent. Snake River sockeye (hatchery and wild combined) had a survival rate of 43.4 percent, compared to the long-term average of 40.7 percent.
On the Columbia River from McNary Dam to Bonneville Dam, yearling hatchery Chinook had a survival rate of 78.5 percent this year, compared to the long-term average of 81.2 percent. Columbia River hatchery steelhead had a survival rate of 60.6 percent, compared to the 76.4 percent long-term survival rate. And Columbia River sockeye (hatchery and wild) from Rock Island Dam to Bonneville Dam had a survival rate of 73.7 percent, compared to the long-term average of 50.6 percent.