The National Marine Fisheries Service and the Pacific Northwest Regional Commission cooperated in funding a study of the Columbia River estuary from 1977 through 1980. The objectives of this study were:
- Define the migrational and behavioral characteristics of juvenile salmonids from releases through the estuary
- Assist in evaluating hatchery production techniques and procedures in the year of release
- Define and monitor juvenile survival to the estuary for selected stocks and to compare this survival to adult returns to the hatchery and fishery
In addition, sampling for juvenile salmonids was conducted in the spring and summer of 1980 in an area of the ocean extending from Tillamook Bay, Oregon, to Copalis Head, Washington, and from 6 to 48 km offshore.
In 1980, we conducted beach and purse seines at rkm 75 and purse seines at rkm 16 and at nearshore areas of the Pacific Ocean adjacent to the Columbia River mouth. We captured 120,203 subyearling Chinook salmon 18,388 yearling Chinook salmon, 24,348 coho salmon, and 13,877 steelhead. Approximately 4.5% of the total catch was marked fish. Additionally, 2,714 juvenile salmonids, of which 97 were marked, were recaptured in the ocean sampling. These marked fish were used to obtain movement rates, recapture rates, survival estimates, and biological samples. Major results were as follows:
- The peak of migration past rkm 75 for hatchery¿reared chinook and coho salmon and steelhead was during the first 2 weeks in May. Fluctuations in catch of the subyearling chinook salmon migration were directly attributable to the magnitude and timing of hatchery releases.
- Wild stock yearling and subyearling chinook salmon migrated past Jones Beach from late March to late June and late May through September, respectively.
- Movement rates varied considerably between groups, but on the average were the same as in past years¿11 to 32 km/day from release site to the estuary.
- Transporting juvenile fall chinook salmon downstream past eight dams on the Columbia and Snake Rivers may have increased their survival by as much as 277%.
- Fall chinook salmon from Bonneville Hatchery fed Oregon Moist Pellet No. 4 appeared to survive at twice the rate as those fed Oregon Moist Pellet No. 2.
- Based on recoveries of Washougal chinook salmon and Willamette steelhead, smaller individuals within populations released from hatcheries may not have survived as well as larger individuals during their migration to the estuary.
- A substantial decrease in catch rates in the estuary of all salmonids occurred after 19 May 1980, coincident with high turbidity created by the volcanic eruption of Mount St. Helens. The number of subyearling chinook salmon captured after 19 May 1980, was about 50% lower than in comparable periods in 1978 and 1979, even though similar numbers of fish had been released from hatcheries. No dead or moribund fish were observed in 1980, but symptoms of gill irritation were observed during the period of high turbidity.
- Most juveniles were actively feeding as they passed Jones Beach. Average stomach fullness was about 50%. Individuals migrating during periods of high turbidity showed a decrease in stomach fullness.
- Catches of resident fish species, incidental to the research objectives, were as much as 100 times greater in late May and June 1980 than in similar periods in past years.
- Greater than 95% of the juvenile salmonids caught in the nearshore area adjacent to the Columbia River mouth were subyearling chinook salmon.
- In the offshore ocean area, steelhead were found only in late May and early June and to the north of the Columbia River. Chinook and coho salmon had a fairly uniform north-south distribution over the entire sampling area and were predominantly found from 6 to 25 km offshore.