| Abstract/Description or Keywords |
The Hill Creek Spawning Channel (HCSC) was constructed as partial compensation for the loss of spawning habitat that occurred from the construction of Revelstoke Dam. The estimated number of annual fish losses includes 500,000 kokanee (Oncorhynchus nerka), 4,000 bull trout (Salvelinus confluentus) and 1,000 rainbow trout (Oncorhynchus mykiss; Lindsay 1982). Historically, Hill Creek supported both migratory (approximately 100 adults) and resident rainbow trout, but was primarily used by migrants for spawning and rearing (Lindsay 1982). Rainbow trout monitoring studies were conducted at HCSC in 2004 and 2005. This report reviews and summarizes the 2005 rainbow trout monitoring program at HCSC. Main objectives were to determine: i) the number and size of spawners; ii) juvenile densities before and after scarification; and, iii) the number of juveniles emigrating from the channel during summer. Recommendations for improvement and future monitoring are also provided. Redd surveys and resistivity counter data show that Hill Creek currently supports two types of migratory rainbow trout: a smaller, primarily insectivorous type and a larger, piscivorous type. This is significant because piscivorous rainbow trout were not observed in Hill Creek prior to the construction of the spawning channel. The number of rainbow trout redds observed in 2005 was 69, similar to that observed in 2004. Preliminary results obtained from a resistivity counter located at the outlet of HCSC in 2005 estimated a minimum escapement of 35 adult rainbow trout. However, the counter malfunctioned for a portion of the spawning run. Overall, scarification did not seem to have an impact on juvenile rainbow trout densities in HCSC. In 2005, the estimated rainbow trout population in HCSC did not change after scarification (approximately 13,500 fish). In 2004, the post-scarification rainbow trout population was approximately half of that observed pre-scarification. Population changes may be attributed to the variability observed in most salmonid population studies from year to year. The presence of higher numbers of rainbow trout juveniles in HCSC compared to Hill Creek suggests that that the channel may be attractive spawning habitat for adults, as well as rearing habitat for fry. In total, 281 and 149 juvenile rainbow trout were captured in traps upstream and downstream of the spawning channel between 15 July and 7 August, respectively. During this period an estimated 2,129 rainbow trout moved downstream into the spawning channel and/or Hill Creek proper from spawning locations upstream. In contrast, approximately 558 rainbow trout juveniles moved downstream out of the spawning channel past Fence #3. Fry from upstream of HCSC were smaller, suggesting that they may be the progeny of smaller migrants or stream resident adults, rather than the piscivorous type. The downstream migration of rainbow trout captured in traps set in 2005 was observed to be within Hill Creek’s historical peak emigration period (26 July to 19 August; Lindsay 1982). However, live traps were removed on 7 August 2005 prior to scarification, and the later extent of the out-migration period could not be ascertained. Stream margins and/or pools located in HCSC may be important refuge habitats for fry during scarification. The majority of rainbow trout and bull trout were captured in the margins of the spawning channel, where overhanging vegetation and slower velocities were present. Sculpins were usually captured mid-channel. One mountain whitefish was captured at a site downstream of HCSC near a back eddy with overhanging vegetation. The number of bull trout decreased slightly from July to August (similar to age-1+ and age-2+ rainbow trout) during both sample years. Bull trout are fall spawners, and the age-0+ juveniles are larger than age-0+ rainbow trout in mid-summer and therefore, may be inclined to move out of the channel to seek suitable habitats for larger juveniles; this may occur with the large rainbow trout as well. Changes in the catch of sculpin (Cottus spp.) pre- and post-scarification and between years may be due to difficulties in obtaining accurate catch-rates for this species using electrofishing gear. Hill Creek Spawning Channel, rainbow trout, Oncorhynchus mykiss, juvenile, density, scarification, bull trout, Oncorhynchus confluentus, sculpin |
