Science Advisory Report 2016/050
Recovery Potential Assessment of Bull Trout, Salvelinus confluentus (Saskatchewan–Nelson rivers populations)
Summary
- In Alberta, the range of the Saskatchewan – Nelson rivers populations of Bull Trout within the basins of the Oldman, Bow, Red Deer, and North Saskatchewan rivers has contracted to the foothills and east slopes of the Rocky Mountains.
- Many of the Bull Trout populations have been declining over the past century. The total number of adults in all populations in this Designatable Unit is between 6,359 and 21,700 total mature individuals, with individual population estimates ranging from 10 to 1,275 mature individuals.
- In Alberta, there are three Bull Trout life history types; stream residents, fluvial (residing in larger free-flowing streams or rivers as adults, returning to headwater streams to spawn) and adfluvial (residing in lakes as adults, returning to headwater streams to spawn).
- The status of most of the Bull Trout populations in DU 4 is Poor. Bull Trout have been extirpated from seven HUCs (hierarchical hydrological units within watershed boundaries). Population status is Good in three HUCs, Fair in three HUCs and Poor in the remaining 32 HUCs.
- Habitat occupied by Bull Trout is characterized as cold, clean, complex and connected. Groundwater upwellings are an important component of Bull Trout habitat for all life history types.
- Redds created by females for spawning and the initial development of eggs and alevins meet the SARA definition of residence.
- The greatest threats to the long-term survival and recovery of Bull Trout in DU 4 are related to habitat fragmentation, habitat removal and alteration, competition from introduced salmonids, mortality related to fishing, climate change, in addition to the interactive and cumulative effects of these threats.
- Activities that have a moderate or higher probability of jeopardizing survival or recovery include in-water works (e.g., watercourse crossing, shoreline and streambank modifications, construction of barriers), linear development, forestry development, mineral aggregate and hydrocarbon exploration, extraction, and production, water management activities, and urban development.
- The dynamics of Bull Trout populations are particularly sensitive to perturbations that affect survival of immature individuals. Harm to these portions of the life cycle should be minimized to avoid jeopardizing the survival and future recovery of Saskatchewan – Nelson rivers populations.
- Demographic sustainability (i.e., a self-sustaining population over the long term) was used as a criterion to identify recovery targets for Bull Trout. Under conditions with a 15% chance of catastrophic mortality event per generation and a quasi-extinction threshold of 50 adults, abundance needs to be at least 1.9 million adult Bull Trout, requiring 510 km2 of suitable habitat. Targets for alternative risk scenarios ranged from about 95 adults to about 10 million adults and about 14,000 m2 to about 4,300 km2 of suitable habitat, respectively. Estimates are highly sensitive to the extinction threshold, the probability of catastrophic mortality, and the ratio of individuals from small and large-bodied growth trajectories in the population.
- A number of key sources of uncertainty exist for this species related to life history parameters, population connectivity and abundance estimates, the quantity and quality of available habitat and the potential impacts of threat mitigations.
This Science Advisory Report is from the June 15, 2016 Recovery Potential Assessment of Bull Trout, Salvelinus confluentus (Saskatchewan – Nelson rivers populations). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.
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