Survival study confirms 94 percent salmon passage through Rock Island

by Rachel Hansen | Nov 08, 2021

The results are in: More than 94 percent of young Chinook salmon last spring passed safely through Rock Island Hydro Project on their way to the ocean.

The 10-year study tracked the yearling spring Chinook from just below Rocky Reach Hydro Project, through Rock Island reservoir and dam, to 1,000 feet below the dam. The goal was to measure at least 93 percent survival. The final result was 94.45 percent.

“To achieve 94.45 percent, that’s something Chelan County can be proud of,” said Fish and Wildlife Manager Alene Underwood. “Regardless of river flows and conditions over the last 10 years, we’ve proven that these operations result in the same great survival rates.”

Chelan PUD tagged the yearling Chinook with battery-powered tracking devices the size of a grain of rice, about 60 percent smaller than tags used in previous studies.

“It’s less of a burden on the fish, so we’re more confident that fish aren’t influenced by the presence of the tag and will behave as they normally would,” said Lance Keller, senior fisheries biologist at Chelan PUD.

The study showed researchers how salmon pass through Rock Island. More than 80 percent of juveniles pass through the turbine routes. Many of the turbines have been improved over the years to be more fish-friendly. The remaining fish travel through one of the 31 spill gates, some of which are configured to spill water from the top few feet of the river where young fish tend to travel.

In 2010, Chelan PUD achieved similar survival rates at Rock Island: 96.8 percent survival for steelhead, nearly 94 percent for spring chinook and 93.3 percent for sockeye. Rocky Reach achieved similar survival rates in 2011. A yearling Chinook study at Rocky Reach is planned in 2023.

The survival studies are required every 10 years by the habitat conservation plans (HCP) for Rocky Reach and Rock Island hydro projects. Chelan PUD developed the plans cooperatively with state and federal fisheries agencies and tribes.

“I give a lot of credit to our stakeholders,” Underwood said. “These are 50-year plans we’ve committed to. Our partners had the forethought to look at the long game of salmon protection and certainty for operating our hydro projects to produce carbon-free, renewable hydropower.”

Chelan and Douglas PUDs are the only hydropower producers in the nation with habitat conservation plans under the Endangered Species Act. The plans commit the PUDs to a 50-year program to ensure that its hydro projects have no net impact on the upper Columbia River salmon and steelhead runs.

Achieving “no net impact” means that Chelan PUD strives to maintain the same salmon survival rate as if the dams weren’t there. This is done in three ways: strict standards for juvenile and adult survival through the project, hatchery fish production to account for juvenile fish mortality that occurs at the project, tributary funding for habitat restoration, and predator control. The PUD spends about $32-37 million annually for these programs combined.

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