Distribution and Abundance of Native Trout in the Wildhay River Watershed, 2022–2023
Final Report
Author(s)
Nikita Lebedynski, M.Sc., P.Biol.
Summary
Athabasca rainbow trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus) abundance and distribution have decreased from historical levels in Alberta. These species are listed under the federal Species at Risk Act, which identifies many anthropogenic threats to native trout in the province. Alberta’s Native Trout Recovery Program is a collaboration of government and non-government organizations tasked with assessing native trout populations and recovering at-risk populations. The Wildhay River watershed was identified through the Native Trout Recovery Program as a priority for inventory to provide current fisheries information on at-risk Athabasca rainbow trout and bull trout populations. The Alberta Fish Sustainability Index (FSI) is a standardized process of assessment that provides the framework within which fishery inventories must occur for greatest relevance to government managers and planners. Our objective was to describe fish distribution, abundance, and habitat in the Wildhay River watershed of Alberta, with emphasis on native Athabasca rainbow trout and bull trout to address data deficiencies for these FSI priority species.
From July 19 to August 7, 2022, and July 25 to August 25, 2023, we sampled fish with backpack electrofishing gear and collected habitat data at 95 sites randomly distributed throughout ten Hydrologic Unit Code (HUC) 10 sub-watersheds: Ice Water Creek, Jarvis Creek, Lower Wildhay River, Middle Wildhay River, Moberly Creek, Mumm Creek, Pinto Creek, Rock Creek, South Wildhay River, and Upper Wildhay River. These HUC 10 sub-watersheds make up the greater Wildhay River HUC 8 watershed.
We captured 383 fish, including 220 rainbow trout ranging in size from 44 to 259 mm fork length (FL). Rainbow trout was the most widely distributed species we captured. We detected them in seven HUC 10 sub-watersheds and at 27 of the 95 sites sampled. The Middle Wildhay River HUC 10 had the highest mean relative abundance (fish per 300 m) of immature (<142 mm FL) and non-immature rainbow trout at 9.0 (Confidence Interval [CI] = 1.9–18.1) and 3.0 (CI = 1.3–4.9), respectively. We captured 57 bull trout (63–255 mm FL) in four of the HUC 10 sub-watersheds and at 11 of the 95 sites. The Ice Water Creek HUC 10 had the highest mean relative abundance (fish per 300 m) of immature (<150 mm FL) bull trout at 3.4 (CI = 0.0–8.2). The Upper Wildhay River HUC 10 had the highest mean relative abundance (fish per 300 m) of non-immature bull trout at 0.7 (CI = 0.0–2.1). Sixty sites had zero fish captures of any species. Zero-catch sites occurred across all HUC 10 sub-watersheds but were concentrated in the upper, more alpine, sub-watersheds of Mumm Creek, Rock Creek, South Wildhay River, and Upper Wildhay River.
Stream substrate composition in the headwaters of the Wildhay River HUC 8 watershed was dominated by gravel and cobble, substrates preferred by rainbow and bull trout for spawning, while lower reaches were characterized by finer sediments. Suitable thermal habitat for bull trout was found throughout all HUC 10 sub-watersheds, while many headwater sites had temperatures below the preferred range for rainbow trout.
Our study provides current information on stream habitats, and the abundance and distribution of at-risk Athabasca rainbow trout and bull trout, FSI priority species, within the Wildhay River HUC 8 watershed. This information is useful to land managers who must balance the diverse values of the land base and is critical for the conservation of native fish species that are particularly sensitive to habitat degradation.