Science Advisory Report 2018/013

Recovery Potential Assessment of Rainbow Trout, Oncorhynchus mykiss (Athabasca River Populations)

Summary

• Native Athabasca River populations of Rainbow Trout are found in the upper reaches of the Athabasca River in Alberta. They are found in 19 HUC8s (hierarchical units within watershed boundaries).
• Many of the Athabasca Rainbow Trout populations have been declining over the past century. The total number of adults in all populations is estimated at 65,175 total mature individuals, with individual population estimates ranging from 45 to 9,497 mature individuals.
• There are two Athabasca Rainbow Trout life history types; stream residents and fluvial (residing in larger free-flowing streams or rivers as adults, returning to headwater streams to spawn). Stream residents are the dominant life history type. There are no known native adfluvial populations (residing in lakes as adults, returning to headwater streams to spawn).
• The status of most of the Athabasca Rainbow Trout populations is Poor. Population status is Good in one HUC, Fair in three HUCs, Poor in 13 HUCs and Unknown in the remaining two HUCs.
• Habitat occupied by Athabasca Rainbow Trout is characterized as cold, clean, and well oxygenated. Groundwater upwellings are an important component of Rainbow Trout overwintering habitat.
• 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 Athabasca Rainbow Trout are mortality related to fishing, sedimentation, habitat fragmentation, introduced salmonids and climate change. These are interactive threats.
• Activities that have a moderate or higher probability of jeopardizing survival or recovery include: watercourse crossings (e.g., bridges, culverts, open cut crossings); shoreline and streambank work (e.g., stabilization, shoreline protection); mineral aggregate, oil and gas exploration, extraction and/or production; instream works (e.g., channel modifications, watercourse realignments, dredging, debris removal); and structures in water (e.g., boat launches/ramps, docks).
• Based on the modelling, the dynamics of Athabasca Rainbow 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 the populations. Sensitivity of adults to fishing related mortality is evident from long-term studies within the watershed and should also be minimized.
• Demographic sustainability (i.e., a self-sustaining population over the long term) was used as a criterion to identify recovery targets for Athabasca Rainbow Trout. Under conditions with a 15% chance of catastrophic mortality event per generation, a quasi-extinction threshold of 50 adults and a probability of extinction of 1%, abundance needs to be at least 270,000 adult Athabasca Rainbow Trout, requiring 144.76 km² of suitable habitat when the population is made up of entirely stream resident individuals. Targets for alternative risk scenarios ranged from about 83 adults to about 549,823,287 adults and about 0.18 km² to about 241.2 km² of suitable habitat (suitable habitat calculated for a 1% probability of extinction only). 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 December 8-9, 2016 Recovery Potential Assessment of Rainbow Trout, Oncorhynchus mykiss (Athabasca River populations). Additional publications from this meeting will be posted on the DFO Science Advisory Schedule as they become available.

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