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1950s & 1960s Productivity

Idaho Fish & Game Report to the Director 5/1/98

Were the 1950s and 1960s unusually productive years for Snake River spring and summer chinook?

Conclusion: The 1950s and 1960s may have been somewhat more productive than recent years, but we have no evidence that they were unusually productive to the extent that they explain declines in Snake river chinook.

Schaller et al.(1996) assessed historical patterns of productivity and survival rates for the aggregate upriver Columbia River wild spring chinook, 1939-1990 brood years. The upriver aggregate is all interior Columbia River spring chinook populations originating upstream of Bonneville Dam. This aggregate was dominated by Snake River and upper Columbia river populations prior to the major impacts of dam construction and operation; the downriver populations historically were a relatively small component. Therefore, the aggregate patterns, in large part, reflect the effect of hydropower system development on productivity and survival rates.

Schaller et al. (1996) concluded that spawner and recruit data of the aggregate upriver run of wild spring chinook for brood years 1939-1990 provided little or no evidence of a long-term, gradual decline in productivity and survival rate of upriver spring chinook remained fairly stable from early hydropower development (1939) until the era of major hydropower development (about 1970), when major declines began. The same conclusions were reached by PATH in the 1996 Retrospective Analysis Conclusions document. Productivity is defined in these studies as the number of recruits per spawner in the absence of density dependent mortality; survival rate is defined as the residuals about the fitted spawner-recruitment relationship. The following discussion is adapted from Schaller et al. (1996).

Analysis of covariance and least square means tests in Schaller et al. (1996) found no differences in productivity estimate between the periods 1939-1949, 1950-1959, and 1960-1969. Productivity estimates from the periods 1970-1979 and 1980-1990 were significantly less than any of the early periods. This aggregate provides a longer time series of R/S data than any of the index stocks. The indices of climate change over the Pacific Ocean, which Beamish et al. (1997) linked to sockeye salmon (O. nerka) production, varied widely from 1939 to 1970. Interestingly, the productivity of the aggregate remained fairly stable (relative to post-1970) through these decades and then decreased coincident with the period of major hydropower development and operation.

Plots of survival rate indices for the aggregate upriver run (Schaller et al. 1996) also indicated the major declines in survival rate began about 1970. In the period 1939-1949, annual survival rates ranged from about 40% to 200% of the 1939-1969 average. Annual survival rates in the 1950s and 1960s ranged from about 60% to 200% of the 1939-1969 average. After 1970, survival rates have ranged from less than 10% to 70% of the 1939-1969 average.

In addition, Deriso, et al. (1996) estimated a common year effect between Snake River spring/summer chinook and downriver spring chinook populations for the 1960-1990 brood years. Downriver populations were from the John Day, Warm Springs, Klickitat and Wind rivers, above one to three dams. Examination of the common year effects indicates that the 1950s and 1960s had generally better survival (presumably in the ocean phase), than the 1970s and 1980s, but that both periods had good and poor years.

Their Status and Recovery Options
Report to the Director Idaho Fish & Game 5/1/98
Issue Paper: 1950s and 1960s Productivity

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