In August 1996, we PIT tagged and released 1,360 wild chinook salmon parr in the South
Fork of the Salmon River and two of its tributaries in Idaho. During spring and summer 1997,
the overall adjusted percentage of PIT-tagged fish from Idaho detected at six downstream dams
averaged 18.3% (range 16.0 to 27.3% depending on stream of origin). Peak detections of all
wild spring/summer chinook salmon
... [Show full abstract] smolts (from Idaho and Oregon) at Lower Granite Dam
occurred during variable but increasing river flows in April. High river flows from mid-April to
mid-May moved most of these fish through Lower Granite Dam, with 50 and 90% passage
occurring on 24 April and 21 May, respectively. From 1989 to 1996, peak detections of wild
spring/summer chinook salmon smolts were highly variable and generally independent of river
flows before about 9 May at this dam; however, during these years (including 1997), peak
detections of wild fish coincided with periods of peak flow at the dam from 9 May to the end of
May. In both 1995 and 1996, in excess of 90% of the wild fish had migrated past Lower Granite
Dam by the time peak flows occurred in June. In 1989, we observed a period of peak detections
of wild fish that coincided with peak flows at the dam in June. After examining chinook salmon
smolt passage timing at the dams over the last 9 years, it has become clear that flow is only one
of several factors that influence passage timing. Other factors, such as annual climatic
conditions, water temperature, turbidity, physiological development, variability in stock
behavior, fish size, and other yet unknown conditions may equally affect wild smolt passage
timing at dams. As additional environmental monitors and traps are installed in study streams,
we will be able to more accurately monitor parr and smolt movements out of rearing areas and
examine the relationships of these movements to environmental parameters within the streams.
Mapped over time, this information will provide the basis for accurately predicting the
migrational timing of different wild stocks as they migrate downstream through the hydropower
system.