First records of two freshwater mussel Species at Risk, Mapleleaf (Quadrula quadrula) and Lilliput (Toxolasma parvum), in the Canard River, Ontario, with implications for freshwater mussel recovery in the Detroit River

Résumé

Freshwater mussels of the family Unionidae are among the world’s most imperilled animals. A third of Canadian species have been assessed by the Committee on the Status of Endangered Wildlife in Canada as Extirpated, Endangered, Threatened, or Special Concern, with losses attributed to natural system modifications such as damming, pollution, exploitation for buttons and pearls, urbanization, and the introduction and subsequent effects of aquatic invasive species. In the Great Lakes basin, the introduction of dreissenid mussels in the 1980s caused catastrophic declines, with remnant populations restricted to lotic riverine habitats. In southwestern Ontario, the Canard River is the largest remaining direct tributary of the Detroit River that could provide a source of mussels to aid natural recovery. In 2019, nine sites in the Canard River were sampled using a timed-search approach (4.5 person-hours/site) with a combination of tactile searching by hand and mussel scoops (7-mm mesh) or underwater viewers. The search yielded 362 individuals of eight species, including two Species at Risk, Mapleleaf (Quadrula quadrula) and Lilliput (Toxolasma parvum), which had never been previously recorded in the Canard River.