Distribution of Bull Trout in the Upper Little Red Deer River Watershed, 2023

Final Report


Lindsay Marley, B.Sc., P.Biol.


Bull trout (Salvelinus confluentus) abundance and distribution in Alberta have decreased significantly from historical levels and this species (Saskatchewan-Nelson River population) is listed as Threatened in Canada under the Species at Risk Act. Anthropogenic threats have been identified as leading causes to the decline of bull trout, including habitat alteration, fragmentation, sediment introductions, non-native fish stocking, hybridization, and angling mortality.

Bull trout recovery plans acknowledge several data gaps, including distribution, community composition, and abundance within the species’ range. Further research is therefore needed to inform priorities for the conservation of this native species. The Upper Little Red Deer River (Hydrologic Unit Code [HUC] 10) has been identified as a priority for bull trout inventory work by Alberta’s Native Trout Collaborative. Bull trout have been historically captured in the upper reaches of this region, but no watershed-scale assessment has been completed. Our objective was to describe fish distribution, abundance, and habitat in the Upper Little Red Deer River HUC 10 with emphasis on native bull trout and other salmonid species to address data deficiencies in this region. From July 24 to August 31, 2023, we sampled fish with backpack electrofishing gear and collected habitat data at 15 randomly distributed sites. From May to October 23, stream temperature was recorded at 30-minute intervals at six stations distributed within the sub watershed. We also completed two stream crossing assessments to evaluate crossing integrity and species distribution above and below each culvert.

Overall, we captured 2,122 fish during electrofishing at survey and stream crossing assessment sites. Of the 13 species captured, brook trout (Salvelinus fontinalis) and longnose dace (Rhinichthys cataractae) were the most abundant. Among salmonids, only two bull trout, the focal species of our study and the only native trout, were captured at two of the 15 sampling sites. Similarly, native mountain whitefish (Prosopium williamsoni) occurred at only three sites. In contrast, the non-native species, brook trout and brown trout (Salmo trutta), were more widely distributed in the sub-watershed, occurring at 14 sites and nine sites, respectively. Stream substrate composition was primarily cobble and large gravels, habitat qualities that are suitable for bull trout. Stream crossing assessments at Owl Creek and an unnamed tributary to the Little Red Deer River do not suggest any limitation for bull trout migration.

Results from our study suggest very low bull trout abundance and limited distribution in the Upper Little Red Deer River HUC 10 sub-watershed with high occurrence of non-native salmonids (i.e., brook trout). Our study provides updated information on stream habitats and the abundance and distribution of bull trout and other fish species within this sub-watershed. This information will help prioritize watersheds for native trout habitat restoration in Alberta.

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