BOISE, Ida. — Idaho Fish and Game biologists expected few sockeye to return to Idaho this year, and midway through the run, the number of fish crossing the dams is lower than expected. The exact number of Idaho fish returning is difficult to determine because few of the fish have electronic PIT tags that help biologists monitor the run.
“With most of the returning Snake River sockeye currently making their way through the Columbia River to Idaho, over the next couple of weeks, we should get a better idea of whether our Snake River sockeye salmon were affected by the same processes that led to the downgrade in the Columbia River-wide sockeye forecast at the end of June,” said John Powell, Fish and Game fisheries research biologist.
“Through July 8, we have observed a single PIT tagged fish pass Bonneville Dam,” Powell said. “With only one PIT tag, we are unable to make a precise estimate of the number of Snake River sockeye salmon that are currently in the Columbia River.”
On average about 75 percent of the sockeye destined for Redfish Lake have passed Bonneville Dam on the Columbia River on or before July 4. But Idaho’s sockeye are typically mixed with other sockeye that continue up the Columbia, while Idaho’s fish proceed up the lower Snake River and are counted through its four dams.
Through July 7, eight sockeye had crossed Lower Granite Dam, which is about 25 miles downstream from Lewiston and the last dam the fish cross before reaching Idaho.
“It is still early for most of these fish to have made it to Idaho, approximately 50 percent of the run usually crosses Lower Granite Dam in the two weeks following of July 4, thus, we will know more about the size of the Snake River sockeye run in the next couple of weeks,” Powell said.
A major factor in the low forecast and likely low return revolves around how long sockeye spend in the ocean before returning to the Sawtooth Basin near Stanley. Typically, about 83 percent of Fish and Game ’s hatchery-released sockeye and 75 percent of the naturally produced fish spend two years in the ocean, so most of this summer’s return went to the ocean in 2017.
Post-release survival of young sockeye reared at Springfield Hatchery was the lowest in 2017. Only 16.4 percent survived the downstream migration to Lower Granite Dam, which is still about 400 miles from the Pacific Ocean. Biologists also estimated that 2017 had the second-smallest number of natural-origin juveniles leaving Redfish Lake since 2002.
Idaho’s sockeye face a long and arduous journey. They must travel about 900 miles and 6,000 vertical feet to return to their spawning sites in the Sawtooth Basin. In 2018, the first sockeye arrived to the Redfish Lake Creek trap on July 26.
A total of 276 sockeye crossed Lower Granite Dam in 2018. Of those, 113 completed their migration to the Sawtooth Basin. The 10-year average is 620 sockeye returning to the Stanley area.