We PIT tagged wild spring and summer chinook salmon parr in the Snake River Basin in 1991 and subsequently monitored these fish during their smolt migration through Lower Granite, Little Goose, and McNary Dams during spring and summer 1992. This report details our findings, which are summarized below.
- Collection and tagging procedures developed under a previous 3-year project funded by the U.S. Army Corps of Engineers continued to be highly effective and successful during summer and fall 1991.
- We PIT tagged and released 12,086 wild spring and summer chinook salmon parr in 13 streams in Idaho and 3 streams in Oregon from late July to October 1991.
- Total observed mortality from collection, tagging, and 24-h delayed mortality was 1.6% for fish from Idaho streams and 0.5% for those from Oregon streams. No PIT tags were lost during 24-h delayed mortality tests.
- The percentage of released PIT-tagged fish subsequently detected in 1992 at all three dams combined was 10.8% and ranged 5.4-20.7%, depending on stream of origin.
- Significantly more wild fish were detected from Oregon (16.5%)than from Idaho streams (9.1%; P < 0.001).
- Fish that were larger at the time of release were detected at a significantly higher rate the following spring than their smaller cohorts (P < 0.001).
- Juvenile wild fish migrating through the dams in April and May were significantly longer at time of tagging than those migrating in June (P < 0.001). Since we observed this trend in all previous years, we believe that fish size may be an important factor influencing selection of overwinter habitat and/or the dynamics of smoltification.
- Juvenile migration timing of wild spring chinook salmon at Lower Granite Dam was earlier overall than for the previous 3 years. The middle 80% of combined populations passed during 15 April-27 May at Lower Granite, 21 April-1 June at Little Goose, and 1 May-1 June at McNary Dam.
- Juvenile timing was earlier for wild summer chinook salmon than for wild spring chinook salmon at all three dams. The middle 80% of combined populations passed during 11 April-26 May at Lower Granite, 18 April-12 May at Little Goose, and 29 April-31 May at McNary Dam.
- Protracted arrival distributions and small sample sizes made it difficult to statistically quantify small differences in migration timing at Lower Granite Dam between fish from different streams. Consequently, the only statistically significant timing difference we detected was that between the Imnaha River and upper Big Creek juvenile migrants. Imnaha River fish arrived at Lower Granite Dam significantly earlier than those from upper Big Creek (P < 0.05).
- Peak passage periods of the combined populations of wild spring and summer chinook salmon did not coincide with peak river flow periods at Lower Granite Dam, but did coincide with peak river flow periods at Little Goose and McNary Dams.
- Unusually warm weather and high water temperatures in late winter and spring appeared to result in earlier juvenile migration timing for all wild smolts in 1992.
- For wild chinook salmon passing from the fish and debris separators, diel timing varied among dams over the migration season. Slightly more fish exited the fish and debris separators at Lower Granite and Little Goose Dams during daylight hours than at night; however, more than twice as many fish exited the fish and debris separator at McNary Dam during daylight hours than at night.
- There is a dire lack of environmental information on study streams in Idaho and Oregon. Only five U.S. Geological Survey stations recorded flow information and no continuous water temperatures were measured at any of these streams.