Background and Summary: Snake River Chinook

Background and Summary:
Snake River Chinook

Status and Expected Time to Extinction
for Snake River Spring and Summer Chinook Stocks

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7/9/1999 --  --  Download the full report in .pdf format [1]

July 1999 -- Snake River spring and summer chinook salmon once returned in great enough numbers to act as the historical "driver" for all Columbia River Basin spring and summer chinook stocks. Thousands of these fish returned annually to Snake River tributaries in central Idaho and northeast Oregon, provided sustenance to Native American Tribes for millennia, and, in the post-European settlement period, contributed for many years to healthy sport and commercial fisheries.

Unfortunately, Snake River spring and summer chinook numbers have reached precarious levels. In recognition of the species' decline, the National Marine Fisheries Service (NMFS) listed Snake River spring and summer chinook as threatened under the federal Endangered Species Act (ESA) in 1992. Furthermore, NMFS committed in 1995 to making decisions regarding the long-term operations of federal Columbia and Snake River dams that impact ESA-listed salmon by the end of 1999. Whether to breach the four lower Snake River dams, and decisions related to fish harvest, hatchery operations, and habitat degradation are currently being considered in numerous forums throughout the Pacific Northwest and Washington D.C.

A critical consideration in developing a workable solution to save Snake River fish from extinction is the timing of the restoration activities that need to occur. Many of the spring and summer chinook populations have reached such low levels that any sort of delay has a cost. However, as NMFS recently noted, federal models to date do not measure extinction risks because they do not include any scenarios involving stocks becoming extinct. This paper is meant to provide a mechanism to project how long wild Snake River spring and summer chinook salmon can be expected to survive given current conditions.

Two models, the Salmon Recovery Index, or SRI, (Figure a [2]) and the Doomsday Clock, or Clock (Table a) were developed to make salmon spawning escapement data more informative to salmon recovery professionals and the public. The SRI developed in this paper accurately captures the condition of salmon populations. The index condenses the current status of a group of salmon populations into a single reliable number, while the Clock provides a measure of how long salmon may be expected to survive current conditions.

Table a. Summary of extinction statistics for Snake River spring and summer chinook.

The Clock provides a measure of the expected time until extinction for salmon spawning populations, called demes. Using data provided by Idaho Fish and Game, the SRI and the Clock demonstrate that the existence of Snake River spring and summer chinook demes is precarious and that their future appears grim indeed. If present conditions prevail, the Clock predicts that all five brood lines of the Snake River spring and summer chinook will be extirpated between 2008 and 2017 (Table a). Although some salmon should still be returning to spawn in 2017, the listed species will have ceased to exist as a naturally self-sustaining wild animal population. Unless current conditions change for the better, there is only a remote possibility that more than one of the thirteen demes studied will have spawners after 2045. This situation could change for the worse, because the str

Date: 7/9/1999