Science Advisory Report 2020/052

Recovery Potential Assessment for Westslope Cutthroat Trout, Oncorhynchus clarkii lewisi, Saskatchewan-Nelson River populations (DU1)

Summary

• Life history data for genetically pure, stream resident populations of Westslope Cutthroat Trout (WCT) in Alberta were compiled to generate a population model.
• Modelling was used to estimate the impacts of anthropogenic harm to WCT populations, estimate recovery targets for abundance and habitat, and estimate potential recovery timeframes.
• Under most model scenarios, WCT populations were most sensitive to perturbations to the juvenile stage (survival, growth, or habitat) regardless of the assumptions of density-independence, density-dependence, or periodic harm. This indicates that impacts to this portion of the lifecycle, such as fishing mortality or habitat alterations, may be the most detrimental to the population as a whole. As well, improvements to aspects of the juvenile stage may provide the greatest stimulus for population recovery.
• However, the exception to this occurred when an extreme surplus (> 10 times the amount required to support the stage-specific population size) in juvenile habitat or adult habitat existed. With an extreme surplus in juvenile habitat, small perturbations to juvenile habitat did not have much impact on stable adult density; however, perturbations to adult or spawning/YOY (young-of-year) habitat did impact adult density. With an extreme surplus in adult habitat, perturbations to adult habitat did not significantly affect adult density; however, juvenile habitat become even more important.
• Population viability analysis (PVA) was used to assess the minimum viable population (MVP) as a measure of an abundance recovery target. To achieve a 99% persistence probability over 100 years, adult (> 138 mm) population sizes of ~ 1,600, 3,000, and 4,200 were required assuming a frequency of catastrophic events (> 50% decline in population size) of 5%, 10%, and 15% per generation.
• The minimum amount of habitat required to support a population abundance of MVP (i.e., minimum area for population viability) was estimated to be ~ 21, 30, and 37 river km for the respective catastrophe rates based on the upper confidence interval of estimates.
• Recovery time, defined as the time taken to reach MVP from an initial population of 10% of MVP, ranged from 27–33 years across simulations.

This Science Advisory Report is from the December 17, 2019 meeting on Recovery Potential Assessment – Westslope Cutthroat Trout, Oncorhynchus clarkii lewisi, Saskatchewan-Nelson River Populations (DU1). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2020/052 (PDF, 471 KB)

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