In 1993, we PIT tagged wild spring/summer chinook salmon parr in the Snake River Basin and monitored the migration of these fish through Lower Granite, Little Goose, Lower Monumental, and McNary Dams during spring, summer, and fall 1994. This report details our findings, which are summarized below.
- We PIT tagged and released 8,065 wild chinook salmon parr in 15 streams in Idaho in July and August 1993.
- Average overall observed mortality from collection, tagging, and 24-h delayed mortality was 2.2%. No PIT tags were lost during 24-h delayed mortality tests.
- Of PIT-tagged fish released in 1994, the overall adjusted percentage subsequently detected at the four dams averaged 13.8% (range 6.6-28.5%, depending on stream of origin).
- Fish that were larger at release were detected at a significantly higher rate the following spring and summer than their smaller cohorts (P < 0.001).
- Wild juvenile fish migrating in April and May were significantly larger at release than fish migrating after May (P < 0.0001).
- At Lower Monumental Dam in 1994, 17 wild chinook salmon smolts were recaptured. Over an average of 268.5 d between release and recapture, these fish had grown an average of 37.6 mm in length and gained an average of 8.5 g in weight.
- At Lower Granite Dam, migration timing of wild spring/summer chinook salmon smolts in 1994 was similar to that in 1990 and 1992, with peak passage in April. However, peak passage of fish from individual streams occurred from late April to late May 1994. In 1994, as in the previous 5 years, wild fish passage was highly variable and generally independent of river flows before mid-May. After about mid May, peak passage of wild fish tended to coincide with periods of peak river flow.
- We have consistently observed a 2-week shift in timing of wild fish at Lower Granite Dam between relatively warm and relatively cold years. In the colder-than-normal years of 1989, 1991, and 1993, 50% of all wild fish passed the dam by mid-May and 90% passed by mid-June. The exception was 1993, when high flows moved 90% through the dam by the end of May. In the warmer-than-normal years of 1990, 1992, and 1994, 50% of all wild fish passed this dam from 29 April to 4 May, and 90% passed by the end of May.
- Diel timing patterns of wild chinook salmon smolts exiting from the fish and debris separators varied among the dams. At Lower Granite and Lower Monumental Dams, significantly more wild fish exited the separators during nighttime hours (1800-0600), than exited during the day (0600-1800). At both Little Goose and McNary Dams, significantly more wild fish exited the separators during daytime hours than exited at night.