Information in support of a recovery potential assessment of Purple Wartyback (Cyclonaias tuberculata) in Canada

Abstract

The Purple Wartyback (Cyclonaias tuberculata) is a long-lived species of freshwater mussel currently found in three watersheds in Canada from lower Lake Huron through Lake St. Clair. The species was assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in May 2021 as Threatened, owing to a small number of extant locations and a continuing decline of habitat quality throughout its range. The species is considered extirpated from two historical locations. The Recovery Potential Assessment provides background information and scientific advice needed to fulfill various requirements of the Species at Risk Act (SARA). This research document provides the current state of knowledge on the species including its biology, distribution, population trends, habitat requirements, and threats. Purple Wartyback is a short-term brooder that is thought to use North American catfishes (Ictaluridae) as hosts for completing its life cycle. It is found in relatively deep, medium to large rivers with moderate to swift currents and occasionally lentic areas over sand, gravel, and cobble substrates. Long-term standardized sampling data suggest that at least two of the three populations in Canada may be growing; however, more years of data are required to span a full generation of this long-lived species. A threat assessment identified the greatest threats to Purple Wartyback in Canada as pollution from agricultural and urban sources, climate change (notably droughts), aquatic invasive species (including dreissenid mussels and Round Goby (Neogobius melanostomus)), and dredging. Limited information exists evaluating the impacts of these threats on Purple Wartyback specifically. Mitigation measures and alternative activities regarding habitat-related threats are presented. Important knowledge gaps remain surrounding the full extent of its distribution within known watersheds, habitat preferences by life stage, mussel-host interactions, and physiological tolerances to environmental conditions and pollutants.