Recovery potential modelling of Northern Brook Lamprey (Ichthyomyzon fossor) – Saskatchewan-Nelson River populations

Abstract

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assessed the Saskatchewan – Nelson River populations of Northern Brook Lamprey (NBL, Ichthyomyzon fossor) as Endangered. Here population modelling is presented to assess the impacts of harm, determine abundance and habitat recovery targets, and conduct long-term projections of population recovery in support of a recovery potential assessment (RPA). The model incorporated parameter uncertainty, environmental stochasticity, and density-dependence into population projections. The analysis revealed that NBL populations were highly sensitive to perturbations in vital rates that affect recruitment such as survival to the larval stage, fecundity, and survival during metamorphosis, as well as ages 1–3 larval survival. As the population growth rate (𝜆𝜆) increased, the sensitivity of all vital rates to perturbation, except for the survival rates of age 4+ larvae, also increased. Population viability analysis was conducted to determine potential recovery targets with demographic sustainability, defined as a self-sustaining population over 60 years, which was achievable with a population size (MPV) of approximately 2,569 [95% confidence interval: 1,110, 4,950] adult females. The current population size, growth rates, and density was unknown for these populations; therefore, a range of initial population sizes and growth rates was used to estimate recovery times and minimum area for population viability (MAPV). The mean recovery time for the lowest initial population sizes and growth rates was 51 years, and the mean MAPV was 6.3 km2 for the lowest density and highest MPV estimates.