Effects of Impoundments and Hydroelectric Facilities on the Movement and Life History of Redband Trout in the Upper Klamath River: A Summary and Synthesis of Past and Recent Studies

In the 77-km section of the Klamath River, between the outflow of Upper Klamath Lake and the Oregon-California Border, the physical and ecological environment of redband trout Oncorhynchus mykiss newberrii has been altered by four hydroelectric dams. Spencer Creek, which enters the Klamath River just upstream of J.C. Boyle Dam, is an important spawning area and source of juvenile recruitment for redband trout in the upper Klamath River. In 1959, the year after J.C. Boyle Dam was completed, fi sh ladder trap counts showed adult redband trout migrated upstream in the Klamath River in large numbers to spawn in Spencer Creek. By 1962, trap counts had declined by at least 90%. Despite this decline, studies conducted in the late 1980s showed that a significant spawning run and juvenile outmigration persisted in Spencer Creek. These findings raised questions about the adult and juvenile life history of the Spencer Creek spawning population. We used radio telemetry and PIT-tag technology to address these questions. Our results show that upstream movement of adult redband trout over the dam to Spencer Creek is rare and suggest that the Keno Reach of the Klamath River is the main source of spawning adults in Spencer Creek. We also found that movement of juveniles from Spencer Creek downstream past the dam has been restricted to those infrequent periods when spill occurs. These findings suggest that the life history diversity displayed by Spencer Creek spawners has been constricted by J.C. Boyle Dam, likely reducing trout abundance and productivity downstream of the dam.