Westslope Cutthroat Trout Population Monitoring in the Upper Oldman River Watershed, 2018–2022
Brad Hurkett and Jason Blackburn
Westslope cutthroat trout (Oncorhynchus clarki lewisi) (WSCT) populations have declined to approximately 5% of their historical distribution in Alberta and the species is listed as Threatened under the Species at Risk Act. In 2018, the Livingstone-Porcupine Hills Land Footprint Management Plan was introduced by the Government of Alberta to manage the long-term cumulative impacts of human footprint on public lands in the Eastern Slopes. The resulting Livingstone Public Land Use Zone encompasses the largest remaining WSCT core area in Alberta. Current land-use restrictions and habitat recovery activities in these critical habitats should benefit native trout fish populations and aid in species recovery. To support recovery actions within the public land use zone, we initiated a multi-year study (2018–2022) to monitor WSCT populations in four high priority critical habitat areas in the upper Oldman River WSCT core area: Livingstone River, upper Oldman River, Dutch Creek, and Hidden Creek. We established 39 electrofishing index sites across these sub-watersheds and surveyed each site with backpack and tote barge electrofishing equipment for five consecutive years.
In each study year, we captured three fish species in all sub-watersheds: westslope cutthroat trout, bull trout (Salvelinus confluentus)), and mountain whitefish (Prosopium williamsoni). Westslope cutthroat trout was the most abundant species, composing the majority of the catch and captured at all sites at least once during the study. Total relative abundance of WSCT (>70 mm fork length) (fish/300m) was highest in the Livingstone River and upper Oldman River watersheds and lowest in the watersheds of Dutch Creek and Hidden Creek. Abundance of adult WSCT (>153 mm fork length) was highest in the Livingstone River and upper Oldman River watersheds, primarily in higher order, mainstem streams. Abundance of juvenile WSCT (>70–<153 mm fork length) was highest in lower order, tributary streams in all watersheds except Hidden Creek, where we captured a higher proportion of adults. Westslope cutthroat trout were generally bigger in larger, higher order mainstem streams and smaller in low order tributary streams in all watersheds. Mean WSCT size was smallest in all watersheds in 2021 and 2022 as we captured a higher proportion of juvenile fish than in previous years.
Results from our sampling series have captured current native trout population data in four of six priority watersheds in the upper Oldman River WSCT core area. This time series dataset can be used to determine the sustainability of each WSCT population, aid in species recovery, and be used as a baseline to monitor long-term changes in WSCT abundance and distribution in response to the new land-use restrictions and proposed habitat restoration activities in the upper Oldman River WSCT core area.