Status of Bull Trout in the Upper Clearwater River- 2004
Bull trout are native to, and widely distributed throughout the upper Clearwater River drainage in west-central Alberta, Canada and include both resident and fluvial life history forms in the study area. As a representative index population for monitoring bull trout population trends provincially; the earliest assessment in the Clearwater drainage was performed in the late 1970s. It has been over a decade since the last assessment of bull trout status in the greater Clearwater River study area. The 2004 study area included the river and its tributaries upstream of the bridge crossing on Highway 54 to the Banff National Park boundary. Study objectives were to estimate the distribution, relative abundance, and size structure of bull trout in the river and its larger stream tributaries, assess use of identified spawning areas, and enable comparison of current findings to the findings of previous studies where practical while assessing new methods arising from a provincial review of bull trout monitoring protocols.
Clearwater River sampling was conducted at three reaches comprising approximately 20 km of river. Float electrofishing mark-recapture abundance estimates were performed in October, after the majority of adult bull trout had likely returned to the river from spawning areas in tributary streams. Third- to fifth-order tributaries to the river were sampled using backpack electrofishing gear in July and August. Sample locations were randomly selected from eligible streams and stratified by stream order and elevation. Forty-seven reaches, or approximately 9 km of stream were electrofished. To assess the variability in electrofishing gear efficiency for the capture of bull trout, removal abundance estimates were conducted at four of the sample locations. Redd surveys were performed at six reference sites and opportunistically at other tributaries in the area. All fish and habitat data collected during the study were entered into the provincial Fisheries Management Information System database, Inventory Project 5466.
No unequivocal evidence for a change in bull trout distribution was observed in either the river or its larger tributaries. Bull trout occurrence in third- and fifth-order streams appeared reduced in 2004 however site selection during previous assessments was non - random and may have biased results. Bull trout abundance at the uppermost reaches of the river had increased since the last assessment in 1992-93 and was estimated at 11-12 fish greater than 100 mm fork length per river kilometre. Mean bull trout catch-per-unit-effort (fish/100 m) in previously surveyed tributary steams was comparable or higher during the 2004 assessment. Maximum size of bull trout captured in the river increased at every reach. Maximum size of bull trout captured in stream tributaries increased since 1992-93 in both Cutoff and Rocky creeks and was comparable at Elk and Forbidden creeks. Estimated efficiency of backpack electrofishing gear for the capture of bull trout at tributary sites varied from less than 10% to nearly 90%. Bull trout use of previously identified spawning reaches was comparable to the maximum use observed during previous surveys at the majority of sites. Evidence of probable bull trout spawning was observed in Cutoff Creek, an area where use was marginal during previous surveys but likely substantial historically.
Results indicate that the bull trout population within the upper Clearwater River study area has likely increased in the last decade. The effect, if any, of differences in study methods between assessments and natural variation in bull trout abundance within the study area on this conclusion is unclear and needs to be considered. Several recommendations for the development of provincial bull trout monitoring protocols were identified.