Downstream Fall Migrations of Native Salmonids from Major Tributaries Associated with the Hells Canyon Complex, Snake River.

摘要

Major tributaries associated with the Hells Canyon Complex and one reference tributary below Hells Canyon Dam were monitored for downstream movements of salmonid fish species during fall months of 1998 and 1999. During 1998, the Wildhorse River and Indian Creek were monitored. During 1999, Indian Creek, Pine Creek, and Sheep Creek were monitored. The Wildhorse River enters the Snake River within Oxbow Reservoir. Indian Creek and Pine Creek enter within Hells Canyon Reservoir, and Sheep Creek enters the mainstem Snake River below Hells Canyon Dam at river kilometer 369 (river mile 229.4). With the exception of Pine Creek, wild rainbow trout were the dominant fish species captured in both weirs. The Pine Creek weir was only operated for a one month period, and was washed out prior to the peak capture of salmonids observed in the other tributaries. Catches of rainbow trout in the other streams increased once water temperatures began to drop below 10 C. Bull trout were not captured in the Wildhorse River or the Pine Creek weirs. In the Indian Creek weir, F1 Bull Trout x Eastern Brook Trout hybrids were the dominant char captured. Two Eastern brook trout and two fish field identified as bull trout were also captured in the Indian Creek weir. The Sheep Creek weir captured five bull trout, including a spawned out female. Species collected in the Wildhorse River and Pine Creek were similar, and collectively included 12 species of fish representing five families. Bridgelip suckers, smallmouth bass, and channel catfish comprised the highest percentage of nonsalmonid species captured. With the exception of one smallmouth bass in the Indian Creek captures, no warmwater fish were captured in either Indian Creek or Sheep Creek. Sheep Creek captures included only three species of fish representing only the Salmonidae family.