Before 1989, there was little detailed knowledge of the migrational timing of wild smolts of Snake River spring and summer chinook salmon Oncorhynchus tshawytscha from individual streams. With the development of the passive integrated transponder (PIT) tag and methods for collecting and tagging parr, acquisition of information on migrational timing became feasible. We PIT‐tagged wild chinook salmon parr in several streams in Idaho and Oregon each summer from 1988 through 1990. Each subsequent spring and summer, we detected surviving smolts on their migration through Lower Granite Dam. We also PIT‐tagged hatchery‐reared parr during fall or late winter and compared their migrations with those of wild fish. Migrational timing of wild smolts through Lower Granite Dam varied for fish from different streams and also differed from hatchery‐reared fish. Generally, wild spring chinook salmon migrated later and over a more protracted period than their hatchery‐reared counterparts. Wild summer chinook salmon migrated earlier than their hatchery‐reared counterparts but also over a protracted period. This study demonstrated that PIT tag technology can be used successfully to monitor migrations of wild and hatchery chinook salmon smolt stocks during their journey to the ocean.

We evaluated Renibaeterium salmoninarum infection in smolts of hatchery and wild spring-summer Chinook salmon Oncorhynchus tshawytscha sampled during most of the outmigration at Little Goose (1988) and Lower Granite dams (1988)(1989)(1990)(1991) on the Snake River and at Priest Rapids and McNary dams on the Columbia River (1988)(1989)(1990) . We sampled 860-2,178 fish per dam each year. Homogenates of kidney-spleen tissue from all fish were tested for the presence of R. salmoninarum antigens by the enzyme-linked immunosorbent assay (ELISA), and homogenates from 10% of the fish were examined by the fluorescent antibody technique (FAT) . Although only 1-11% of fish sampled at a given dam during any l year exhibited lesions characteristic of bacterial kidney disease, 86-100% of the fish tested positive for R . salmoninarum antigen by ELISA, whereas 4-17% of the fish tested positive by the FAT. During most years, a majority (68-87%) of fish testing positive by the ELISA had low R. salmoninarum antigen levels, but in 1989, 53% of positive fish from Lower Granite Dam and 52% from McNary Dam showed medium-to-high antigen levels . For most years, the highest mean antigen levels were measured in fish sampled after 75% of the total out-migrants had passed a given dam . When the largest numbers of fish were being collected for bypass or downriver transportation, mean antigen levels were relatively low .

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