Research Document 2023/087

Recovery Potential Modelling of Purple Wartyback (Cyclonaias tuberculata) in Canada

By van der Lee, A.S. and Koops, M.A.

Abstract

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assessed Purple Wartyback (PWB, Cyclonaias tuberculata) as Threatened in Canada. 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 demonstrated that PWB populations were most sensitive to perturbations to adult survival under most circumstances. As population growth rate (λ) increased the sensitivity of juvenile survival to perturbation increased and surpassed adult survival sensitivity when λ > 1.2. Estimates of the level of harm that would reduce population growth rate to 1 were estimated for populations in the Sydenham and Thames rivers. Population viability analysis was used to identify potential recovery targets. Demographic sustainability, (i.e., a self-sustaining population over 250 years) can be achieved with population sizes of ~2,800 (CI: 1,900–4,000) adults. It was estimated that populations of minimum viable population (MVP) size would require 623.3 m² (CI: 251.9–1,396.9) and 2,900 m² (CI: 301.5–17,166.3) in the Sydenham and Thames rivers respectively. Therefore, there is sufficient habitat to support PWB populations in both systems.

Research Document 2023/087 (PDF, 1,999 KB)

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