Bull Trout Population Status Assessment in the Upper Oldman River Drainage, 2007 - Phase 1 Summary Report


Brad Hurkett


Currently, bull trout (Salvelinus confluentus) distribution in Alberta is restricted to the upper Peace, Athabasca, North Saskatchewan, and the South Saskatchewan River basins. The species has declined in both distribution and abundance since the early 1900s. The decline is generally attributed to human activity including angling pressure, habitat degradation and fragmentation, migratory barriers, and the introduction of non-native species. As a result of the decline in abundance, the species is now ranked as “sensitive” in Alberta and “threatened” under the Endangered Species Act throughout its range in the US (lower 48 states).

Bull trout are known to exhibit 3 main life history strategies: resident, fluvial, and adfluvial. Resident bull trout populations reside within the tributary in which they were reared; fluvial populations spawn in tributaries, but reside in mainstem rivers; and adfluvial populations spawn in the key tributaries, but reside in lakes or reservoirs. As a result of these life history strategies, bull trout have complex habitat requirements and in some cases large home ranges (Post and Johnston 2002). In some drainages, both the resident and migratory life history forms occur. Historically, where resident and migratory forms coexisted within the same drainage, the migratory form was dominant (Fredenberg et al. 2005). In addition, the evolutionary history of bull trout indicates that as an apex predator species the migratory life form was a highly successful strategy (Whitesel et al. 2004). It is suspected that bull trout in the upper Oldman drainage exhibit at least 2 of the 3 life strategies above.

Currently, significant human activity is occurring within the upper Oldman drainage, as well as other East slope drainages. In addition, bull trout distribution within the Oldman Drainage has declined to 33% of historical range, largely since the 1950s (Fitch 1997). Unfortunately, fisheries managers are tasked with managing a species with insufficient data. As a result, a bull trout population assessment is required to determine the status of the species within the drainage.

The Alberta Conservation Association (ACA) is initiating a long-term bull trout (Salvelinus confluentis) population assessment within the upper Oldman (UOM) River drainage to more clearly define bull trout status in the drainage and to also aid in directing bull trout conservation and management in the future. The main objective of the study is to assess the population status of adult migratory bull trout in the UOM river drainage. Phase 1 (2007) focused on collecting preliminary data on adult migratory bull trout from Hidden Creek by intercepting both pre and post-spawning bull trout in conduit fish traps.

In addition, Phase 1 of the UOM bull trout population assessment has coincided with the 2006 and 2007 UOM cutthroat trout population assessment. Coincidental catches of bull trout captured during the cutthroat trout population assessment assisted in the identification of spawning and rearing streams. The 2006 UOM cutthroat trout population assessment and previous redd survey results identified Hidden Creek as a major spawning tributary due to the high density of adult migratory bull trout that were captured at numerous sites throughout the stream. Sites sampled in 2007, suggest that Dutch Creek, Racehorse Creek and the Livingstone River are also key spawning tributaries for migratory bull trout. As a result efforts will focus on intercepting spawning bull trout in these tributaries in 2008. Future efforts (2009 and 2010) will focus on the spatial and temporal identification of spawning areas, migration timing, movement corridors, and overwintering habitat.

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