Technical Report ODFW, 2006. Paper Website abstract bibtex 2 downloads
The physical and ecological environment of redband trout in the Upper Klamath River has been altered by hydroelectric dams. Four dams and five distinct river reaches are currently present in the 48-mile section between the outflow of Upper Klamath Lake and the Oregon- California Border. 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, fish 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 left questions about the extant adult and juvenile life history of Spencer Creek spawning population. We used radio telemetry and PIT- tag technology to address these questions. Our results suggest that, since the construction of J. C. Boyle Dam, upstream movement of adult redband trout to Spencer Creek is uncommon and movement of juveniles from Spencer Creek downstream past the dam may be restricted largely to periods when spill occurs. We also found that the Keno Reach of the Klamath River is the main source of spawning adults in Spencer Creek. In total, these results suggest that diversity of life histories displayed by Spencer Creek spawners has been constricted by the construction of J.C. Boyle Dam. This reduction in life history diversity has likely reduced trout abundance downstream of the dam. These results also show that the extant adult life history is composed largely of a downstream spawning migration in Klamath River to Spencer Creek and a substantial juvenile upstream migration to the Keno Reach.