Recovery potential modelling of Kidneyshell (Ptychobranchus fasciolaris) in Canada

Abstract

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has assessed Kidneyshell (Ptychobranchus fasciolaris) in Canada as Endangered. Sampling data provided by the UMBO (Unionid Monitoring and Biodiversity Observation) network was analyzed to estimate abundance and population growth for Kidneyshell populations in the Ausable and Sydenham Rivers. Population modelling is presented to assess the impacts of harm and estimate abundance and habitat requirements to support viable populations in support of a recovery potential assessment (RPA). The model incorporated parameter uncertainty, environmental stochasticity, and density dependence into population projections. The Ausable River population in the sample sites has a projected adult abundance of 1,129 (95% CI 933–1,360) and an estimated population growth rate of 1.07 (95% CI: 1.02–1.13). The Sydenham River population in the sample sites has a projected adult abundance of 6,949 (95% CI 5,371–9,059) and an estimated population growth rate of 1.13 (95% CI: 1.11–1.15). These abundance estimates are minimum estimates since Kidneyshell can be found outside the sample sites. The population model analysis demonstrated that Kidneyshell populations were most sensitive to perturbations to adult survival under most circumstances. Estimates of the maximum sustainable level of harm (i.e., harm that would not reduce population growth rate to less than 1) were estimated for populations in the Ausable and Sydenham Rivers. Population viability analysis was used to identify requirements for population viability. Demographic sustainability (i.e., a self-sustaining population over the long term) can be achieved with an adult population size of ~ 5,250 (CI: 2,250–9,750) at a 99% probability of persistence over 100 years. Based on current population densities, such a population would require ~ 260 ha (CI: 105–680) in the Ausable River and ~ 50 ha (CI: 22–113) in the Sydenham River. Based on extrapolated population densities at carrying capacity, the population would require ~ 108 ha (CI: 4.7–5,100) in the Ausable River and ~ 10 ha (CI: 0.62– 109) in the Sydenham River. The Sydenham River population in the sample sites currently exceeds this estimate of minimum viable population size (MVP). At current population growth rates, the Ausable River population within the sample sites can reach the MVP in 52 years (CI: 22–167).