Research Document - 2016/099

Recovery Potential Modelling of Bull Trout (Salvelinus confluentus) (Saskatchewan – Nelson rivers populations) in Alberta

By Caskenette, A.L., Young, J.A.M., and Koops, M.A.

Abstract

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has assessed the Saskatchewan – Nelson rivers populations of Bull Trout (Salvelinus confluentus) as Threatened in Canada. Here we present population modelling in support of the recovery potential assessment of the species. Results include a sensitivity analysis, determination of allowable harm, and minimum viable population estimates to inform recovery targets for population abundance and required habitat. The analyses demonstrate that 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. To achieve demographic sustainability (i.e., a self-sustaining population over the long term) under conditions with a 15% chance of catastrophic mortality event per generation and a quasi-extinction threshold of 50 adults at 1% probability of extinction, the adult Bull Trout abundance needs to be at least 1.9 million adult Bull Trout, requiring 510 km² of suitable habitat. Estimates for alternative risk scenarios ranged from ~95 adults to ~10 million adults and ~14,000 m² to ~4,300 km² of suitable habitat, and 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.

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