Migratory characteristics of juvenile spring Chinook salmon in the Willamette River

The objective of this research was to examine in detail the migration of juvenile spring Chinook salmon (Oncorhynchus tshawytscha) in the Willamette River, Oregon. The authors wanted to determine characteristics of seaward migration of spring Chinook smolts in relation to the oxygen supplementation practices at the Oregon Department of Fish and Wildlife (ODFW) Willamette Hatchery and use this information to strengthen the design of the oxygen supplementation project. There is little information available on the effects of oxygen supplementation at hatcheries on the migratory characteristics of juvenile salmon. Such information is required to assess the use of oxygen supplementation as a means of improving hatchery production, its effect on imprinting of juveniles, and finally the return of adults. In the event that oxygen supplementation provides for improved production and survival of juvenile Chinook salmon at Willamette Hatchery, background information on the migration characteristics of these fish will be required to effectively utilize the increased production within the goals of the Willamette Fish Management Plan. Furthermore this technology may be instrumental in the goal of doubling the runs of spring Chinook salmon in the Columbia River. While evaluation of success is dependent on evaluation of the return of adults with coded wire tags, examination of the migratory characteristics of hatchery smolts may prove to be equally informative. Through this research it is possible to determine the rate at which individuals from various oxygenation treatment groups leave the Willamette River system, a factor which may be strongly related to adult return rate.