Annual progress report; Fish culture section; Bioengineering evaluation of retrofitted oxygen supplementation in surface water project; final report 2000

摘要

The Willamette Oxygen Supplementation Project was designed to answer one major question concerning the decreasing salmon runs in the Columbia Basin: Can available technology be used to increase runs of chinook salmon in the Columbia basin in existing hatcheries. It was recognized that the restoration of salmon runs would require both hatchery supplementation and protection of wild salmon habitat. The large financial outlay required for construction of new hatcheries makes this choice undesirable. If the production of existing hatcheries could be augmented by the use of increased densities with oxygen supplementation, this would be the preferred procedure. Willamette Hatchery was chosen for conducting the experimental releases of chinook salmon reared at high densities with oxygen supplementation for several reasons: (1) It was located far upstream, simulating the long migration distances required for Columbia River salmon; (2) Salmon were not required to navigate through a series of dams, which might make the returns less interpretable; (3) Willamette Hatchery had excellent returns, nearly 2% survival, in the years previous to the experiment; (4) Willamette Hatchery had a history of low disease incidence; (5) Willamette Hatchery had a manager and crew interested in the experiment. In 1999, the last of the adult salmon from the experiment returned to the hatchery. From analyses of these returns, a number of conclusions were reached: (1) Numbers of fish surviving to adulthood increased with increased rearing densities and oxygen supplementation; (2) Percent yield, a measure of the efficiency of rearing, decreased with increased rearing density; (3) Baffled raceways were very poor for raising spring chinook salmon; (4) Oxygen supplementation seemed to increase production, even in the lower densities; (5) The most cost-effective method of rearing spring chinook salmon was rearing at high densities with oxygen supplementation.