Abundance and Distribution of Migratory Bull Trout in the Upper Oldman River Drainage
Author(s)
Brad Hurkett, Jason Blackburn, and Trevor Council
Summary
Throughout the last century, Alberta’s bull trout (Salvelinus confluentus) populations have been in decline. This decline is attributed to impacts associated with human activities including angling pressure, habitat fragmentation and degradation, the creation of migratory barriers and the introduction of non-native fish stocks. As a result, the distribution of Alberta’s bull trout is now restricted to headwater drainages along the East Slopes of the Rocky Mountains. In particular, the distribution of bull trout in the Oldman River watershed has been reduced to 33% of its historic range, with the majority of the populations occupying headwater drainages, including the upper
Oldman (UOM) River drainage. Industrial and recreational activities, such as logging and off-highway vehicle use, are currently intensifying in the UOM River drainage and the cumulative effects of these activities have led to the degradation of bull trout habitat. The current status of bull trout in the UOM River drainage remains unclear since few studies have been completed on this population, which therefore complicates the management of the fishery.
Alberta Conservation Association conducted a four-year bull trout population assessment in the UOM River drainage. The study’s objectives were to determine the abundance of migratory adult bull trout, identify the migratory patterns of bull trout, and identify bull trout spawning habitat throughout the drainage. We installed fish traps in four historic bull trout spawning tributaries, Hidden Creek, the lower Livingstone River, Racehorse Creek and Dutch Creek, to capture post-spawn migratory
bull trout. We marked each captured adult bull trout (>300 mm FL) with a transponder tag which permitted us to identify recaptured fish during trapping.
Recapture data allowed us to observe the migratory patterns of bull trout throughout the UOM River drainage. We recaptured several bull trout originating from Hidden Creek in the lower Livingstone River, Racehorse Creek, Dutch Creek, and the lower Oldman River. We also recaptured bull trout originating from Dutch and Racehorse creeks in the lower Livingstone River.
We conducted redd surveys to identify bull trout spawning habitat throughout the UOM River drainage. Since 2008, we have confirmed spawning areas in all historic bull trout spawning tributaries, namely Hidden Creek, the lower Livingstone River, Racehorse Creek, and Dutch Creek. We confirmed additional spawning habitat in the UOM River, the upper Livingstone River, South Racehorse Creek, Savanna Creek, and Daisy Creek. We observed the largest number of bull trout redds in Hidden Creek and fish to redd ratios suggest that they were produced by migratory fish. Bull trout redds observed upstream of Livingstone River Falls, specifically the upper Livingstone River,
and Savanna Creek, were classified as stream-resident redds since migratory fish cannot pass this barrier. In Dutch Creek and Racehorse Creek we observed a greater number of redds than fish captured by our fish traps, indicating that both stream-resident and migratory bull trout spawn in these tributaries.
Over three-quarters of our total fish trap catch was from Hidden Creek, indicating that this is a vital migratory bull trout spawning tributary. The remaining migratory fish were captured in Dutch Creek, Racehorse Creek, and the lower Livingstone River, suggesting that these spawning tributaries contribute fewer migratory fish to the UOM River drainage bull trout population. However, post-spawn fish movements attest to the interconnectedness of the UOM bull trout population and their dependence on all tributaries in the drainage. It is apparent that each bull trout spawning tributary in the UOM River drainage plays a key role in the long-term persistence of the UOM bull trout population and if degradation of these streams continue, bull trout populations may be at further risk.