Figures are listed in table of contents but are not included in draft.

ks/0796 ; 07/01/96 12:00 AM

NOT ON OCLC 6/2010

1952-1994

This report reviews and updates spawner and recruit data for Snake and Columbia River spring/summer chinook [sic] stocks; develops data for index stocks subjected to varying levels of human-induced mortality from hydropower, habitat, and hatchery effects; provides consistent data based on standard methods and spreadsheets; and identifies index stocks, data sources, calculation methods, and assumptions. Numbers of spawners and returning recruits to the mouth of the Columbia River were estimated for 11 index populations from the Deschutes, John Day, Grande Ronde, Salmon, and Imnaha River subbasins using spawning ground surveys, age frequencies, mainstem and tributary harvest rates, and mainstem conversion rates available from the 1950's to present. Average numbers of spawners, recruits per spawner, and spawners per spawner varied substantially from year to year and stock-recruitment functions generally accounted for less than half of this variability. Since 1970, average productivity expressed in terms of recruits per spawner and spawners per spawner was much less in Snake River populations than in lower Columbia River populations. Average number of Columbia River recruits per spawner and spawners per spawner generally declined between the late 1950's and present and the decline was more pronounced among Snake River populations. More intensive analysis of these data based on population-specific interpretations and stochastic risk analyses which incorporate the observed variability is required to project future trends and population responses to management alternatives.

Idaho Dept. of Fish and Game

Oregon Dept. of Fish and Wildlife