In 1978, we continued a study to define and monitor the survival of selected stocks of hatchery reared juvenile salmonids to the estuary. Additional study objectives were to develop a sampling system to evaluate hatchery production techniques and procedures and to define migrational and behavioral characteristics of juvenile salmonids in the Columbia River estuary. The following basic conclusions were reached as a result of our efforts in 1978.
- Primarily due to higher river flows in 1978 subyearling chinook salmon were caught at a lower rate than in 1977.
- The peak subyearling chinook salmon migration (14 June) was 4 weeks later in 1978 than in 1977. The change was caused by later release dates for hatchery reared fish, as the actual rate of movement through the river was faster due to the higher river flow. Migration timing of yearling chinook and coho salmon and steelhead appeared normal; the peaks of migration were 10 May, 17 May, and 17 May, respectively.
- Average movement rates through the estuary were as follows: Subyearling chinook salmon, 15 days; yearling chinook salmon, 11 days; coho salmon 1 day; and steelhead, < 1 day.
- Due to the late starting date, sampling in marine waters provided recaptures of subyearling chinook salmon almost exclusively. Rates of movement into the ocean could not be defined from our limited sampling.
- Peak periods of movement for subyearling chinook salmon took place after sunrise and before sunset; whereas, peak movement for coho salmon took place from mid-morning to early afternoon. Both species showed a cessation of movement during darkness.
- Temporal changes in fork length of subyearling chinook salmon related to the timing of various hatchery releases rather than growth during the freshwater migration, even though there appeared to be a size increase during the outmigration.
- Transporting fish past Bonneville Dam did not appear to increase survival in 1978 during a period of high spill; whereas, a 35% increase in survival was observed in 1977 during no spill conditions. Transportation around Willamette Falls and Sullivan Plant generators produced a 43% increase in survival for yearling chinook salmon.
- Survival rates of four groups of subyearling chinook salmon migrating from Spring Creek and Little White Salmon Hatcheries to RM 72 ranged from 26 to 48%. The lowest survival ra e as coincident with the longest travel time and the lowest Na+K+ATPase level.