Hypotheses for Delayed or Extra Mortalityof Snake River Spring/Summer Chinook
Idaho Fish & Game Report to the Director 5/1/98
Why has barging not worked to recover salmon?
The PATH Preliminary Decision Analysis Report on Snake River Spring/Summer Chinook (Marmorek and Peters 1998; Appendix A, p. 94) defines delayed or extra mortality as any mortality occurring outside the juvenile migration corridor that is not accounted for by:
Both the "BKD" or "stock viability" hypothesis and the "regime shift" hypothesis attribute most the differential decline of Snake River salmon survival to factors other than the hydropower system (p. 39; and Table 4.1-2; Appendix A, p. 105-109). It follows that if delayed mortality due to the hydropower system is low, then the "non-hydro" factors must have had a systematically worse effect on Snake river salmon since the dams were constructed (Table 4.1-2).
These three alternative hypotheses considered in the Preliminary Decision Analysis (p. 38-39) were:
The completion of the Federal Columbia River Power system in the late 1960s through the mid-1970s and it subsequent operation, have increased the direct and delayed mortality of juvenile migrants, resulting in considerably sharper declines in survival rates of Snake River spring and summer chinook stocks (over the same time period), than of similar stocks which migrate past fewer dams and are not transported. This hypothesis follows from Conclusion 3a.2 of the PATH FY96 Conclusions Document:
We are reasonably confident that the aggregate effects of the hydrosystem have contributed to reduced survival rates of Snake River stocks (from spawners to adults returning to the mouth of the Columbia River), during the post-1974 period, as compared to the pre-1970 period. Hydrosystem effects include both direct (e.g., turbine mortality) and indirect effects (e.g., delayed mortality, due to such mechanisms as changes in estuary arrival times).
The hypothesis proposes that
BKD is one possible means by which stock viability may have been reduce. Occasional changes in underlying stock viability may cause some or all of the delayed mortality to remain, even if direct mortality is reduced. The consequence of falling into this category (i.e., "delayed mortality is here to stay") is that it is unknown when or if the impacts will switch back to a [more] benign state. For modeling purposes, we consider this the worst case, which is that these factors will stay in the present less favorable state.
Extra mortality is not related to the hydropower system but is due instead to an interaction with a long term cyclical climate regime shift with a period of 60 years. This regime is believed to have shifted from good to poor during brood year 1975, and is expected to return to above average conditions in 2005. The signatures of a recurring pattern of interdecadal climate variability are widespread and detectable in a variety of Pacific basin climate and ecological systems. These cyclical changes affect ocean temperatures and currents which affect distributions of predators and prey; and broad scale weather patterns over land masses which then affect temperatures, rainfall, snowpacks, and subsequent flows. The changes in conditions could affect various stocks to different degrees with the effect on Snake River stocks being systematically different from lower river stocks. There is nothing we can do to change these patterns, but they are expected over time to provide more favorable and less favorable conditions to species located in different areas.
Appendix 3.6 IDAHO's ANADROMOUS FISH STOCKS:
Their Status and Recovery Options
Report to the Director Idaho Fish & Game 5/1/98
Issue Paper: Hypotheses for Delayed or Extra Mortality of Snake River Spring/Summer Chinook
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