Evaluating the Status and Population Biology of an Imperiled Freshwater Mussel, Purple Wartyback (Cyclonaias tuberculata), in Southern Ontario, Canada

The Purple Wartyback (PWB; Cyclonaias tuberculata) is considered threatened in Canada due to the loss of populations in the Detroit River and Lake Erie and possible declines in remaining populations (Ausable, Sydenham, and Thames rivers). Many aspects of PWB life history and population ecology have not been investigated for Canadian populations. We used data from the Fisheries and Oceans Canada Unionid Monitoring and Biodiversity Observation network to estimate PWB population and life-history parameters in the Sydenham and Thames rivers. This mussel occurred at high density in the Sydenham River, but at low density in the Thames River; however, both populations exhibited positive population growth and strong recruitment. Population growth rate in the Sydenham River was 1.047 (credible interval [CI]: 1.0371.058) from 1999 to 2015, and population growth rate in the Thames River was 1.157 (CI: 1.1001.221) from 2004 to 2017. Estimated annual adult survival rate (mean 6 SE) from catch-curve analysis of empty shells, with measured ages, across both populations was 0.950 6 0.007. Estimated survival from catch-curve analysis of live individuals, with estimated ages, was 0.966 6 0.001 and 0.884 6 0.009 for the Sydenham and Thames rivers, respectively. Our results show that populations of PWB are robust in the Sydenham River and small but growing rapidly in the Thames River.