Pen Rearing and Imprinting of Fall Chinook Salmon, 1986 Annual Report.

Pen rearing studies during 1986 completed the second of three years intended for rearing and releasing upriver bright fall chinook salmon (Oncorhynchus tshawytscha) from two study sites, a backwater and a pond, adjacent to the Columbia River; both areas are located in the Jonn Day Reservoir. Results of this study in 1984 and 1985 showed that fish could be successfully reared in net pens and that growth and physiological development of the off-station reared fish proceeded at a faster rate than in fish reared at a hatchery. Transfer of fish from the hatchery to off-station sites at Social Security Pond (pond) and Rock Creek (backwater) during early March increased the period of rearing in 1986 by about four weeks. The increased period of rearing allowed all treatments of fed fish to reach a minimum weight of YU fish/lb by release. Differences in growth of fed fish between regular density treatments and additional, high density treatments (double and triple the regular densities) were not significantly different (P > 0.05), but growth of all fed fish reared off-station was again significantly better than that of hatchery reared fish (P < 0.05), Mortalities in all groups of fed fish were low. Physiological development of fed fish was similar in all treatments. At release, development of fish at Social Security Pond appeared to be somewhat ahead of fish at Rock Creek on the same dates however, none of the groups of fed fish achieved a high state of smoltification by release. Unfed fish grew poorly over the redring period, and at release were significantly smaller than either fed groups at the off-station sites, or the control groups reared at the hatchery (P < 0.05). Development of unfed fish toward smoltification was much slower than of fed fish. Mortality of all groups of unfed fish, including the barrier net, was relatively low. Health of all fish reared off-station remained good over the rearing period, and no outbreaks of disease were noted. On-site marking and transfer of fish from the hatchery did not appear to have an adverse effect. Estimated costs of rearing fed fish at regular, double, and triple the regular density were lower than for rearing a similar poundage of fish in a hatchery. However, estimated costs using present rearing scenarios in net pens at low densities and in a barrier net were high in relation to all other methods considered