Snake River fall Chinook salmon swim from the sea nearly 600 miles inland to lay their eggs in the mainstem Snake River western Idaho. Here, the eggs hatch, and young Chinook grow up strong before preparing to swim back down through the Snake and Columbia rivers and out to the Pacific Ocean.
Evaluating Actions to Improve the Productivity of Snake River Fall Chinook
As with many populations of salmon and steelhead, Snake River fall Chinook abundance has declined dramatically as a result of over-harvest, dams and other major changes to their river and marine habitats. As salmon hatcheries were built to mitigate the impacts the eight Snake and Columbia River dams had on salmon populations, they too came with risks to wild fish productivity.
The Snake River fall Chinook population was ultimately listed as threatened under the Endangered Species Act in 1992. Soon thereafter, our Western Fisheries Research Center scientists partnered with federal, tribal, state, and private entities to begin monitoring and studying these fish. The objective of this long-running research endeavor has been to use the information gained to help managers understand the variety of impacts that limit the productivity of this population and navigate the complex path to recovery. Work over this 30-year period has included studies to: help dam managers determine optimum flows for Chinook spawning and downstream migration, understand what the Chinook rely on to eat in the rivers and reservoirs, and assess the impacts of predators. See our Snake River Fall Chinook web page for more information.
Some of our current Snake River fall Chinook research is to help determine whether efforts to create a “natural production emphasis area” of the Snake River where wild Chinook primarily go to reproduce will help improve the productivity of the Chinook population. Many Chinook that spawn in the Snake River originate from hatcheries.
Hatchery production is a critical measure to mitigate the impacts of dams and habitat degradation, and in turn address tribal treaty rights to fish and sustain non-tribal fisheries. While hatchery fish can have a positive effect on wild-spawning salmon by increasing a population’s abundance and distribution throughout a river basin, hatcheries may reduce the genetic diversity of a population and limit its reproductive success or ability to adapt to ecosystem changes (see NOAA Hatchery Listing Policy).
Up until 2018, juvenile hatchery Chinook were released in the upper portion of Hells Canyon to influence those fish to return to that area to spawn. The goal was to increase the overall abundance of Chinook, hatchery or wild, spawning in this section of Hells Canyon. In 2018, this release was moved to the Salmon River, a tributary to the Snake River. This next phase of recovery is intended to remove ongoing influence of hatchery fish from the Hells Canyon section of the Snake River to see if the wild-spawning Chinook become more productive over time.
WFRC has partnered with the Idaho Power Company to collect and analyze genetic information from Chinook spawning in the upper reach of Hells Canyon. Results to date show that the wild-born Chinook make-up slightly more than 50% of the spawning population; the rest being hatchery fish. It will take several more years to determine whether fewer hatchery fish spawn here, and if that action increases the productivity of the wild fish.