A new study shows the Yakama Nation’s “reconditioning” effort for steelhead at its Prosser hatchery raises the odds of fish surviving to try to repeat spawn from just 3 percent to about 15 percent, the Yakima Herald-Republic reported.

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YAKIMA — The Yakima River’s steelhead population is getting a boost from an innovative program that helps adult females survive to spawn a second time.

A new study shows that the Yakama Nation’s “reconditioning” effort for steelhead at its Prosser hatchery raises the odds of fish surviving to try to repeat spawn from just 3 to about 15 percent, the Yakima Herald-Republic reported.

Unlike salmon, which die after spawning, many female steelhead try to return to the ocean.

But, exhausted from their upstream journey and spawning, combined with the difficulty of passing dams going downstream, few manage to survive and return.

“This is a natural part of steelhead life history. … We’re just helping them survive,” said Jeff Trammell, a fish biologist for the Yakama Nation and lead author of the study, published in July in the North American Journal of Fisheries Management.

For the past decade, the Yakama Nation has been collecting exhausted adult females as they try to head back to the ocean after spawning and then feeding them for months at the Prosser Hatchery. The process is known as reconditioning.

Then, when the fish are fattened up and ready to spawn again, they are let go.

The tribe has also tried short-term reconditioning and collecting the steelhead and trucking them downstream so they don’t have to spend their energy dealing with the dams.

They found that the long-term rehab program is far more successful than the other techniques, Trammell said. And helping the repeat spawners gives the basin’s threatened steelhead population a genetic boost.

“Clearly, these fish have shown that they have the fitness to get up to the spawning reaches, spawn, and then back downstream,” he said. “Being able to put those genes back out there is definitely fantastic for the population.”

A few fish have even been through the tribe’s Prosser program twice.

Now that scientists have learned what to feed the steelhead, about 60 percent survive.

But for reasons that are still unclear, not all of the steelhead are ready to spawn again the next season, Trammell said.

Those fish head downstream toward the ocean again when released, instead of upstream, he said. Now, scientists are trying to determine from blood tests when the fish are ready to spawn so they only release those that are ready, making the rehab effort even more successful.