Rocky mountain ridged mussel (Gonidea angulata) index site surveys in the Okanagan Basin, British Columbia, 2011-2016

Rocky Mountain Ridged Mussel (Gonidea angulata) is one of only a few species of freshwater mussel in British Columbia, restricted in Canada to the Okanagan Basin. In 2005 this species was listed under the Species at Risk Act (SARA) as Special Concern, and in 2010 it was reassessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as Endangered. As a continuation of previous work and to inform future assessments and conservation efforts in the Okanagan Basin, index sites that were easily accessible and known to have G. angulata were selected to estimate abundance at these areas over time. Mean mussel densities across all index sites from 2011–2016 ranged from 0.11 to 2.82 mussels/m2. Estimates of total abundance at each site ranged between 131 and 3,589 mussels. Mussel density by depth was also examined, and mussels were observed to be in depths between 0.02 and 1.76 m. They were generally found in higher densities in water depths greater than 0.50 m, and typically declined with depths exceeding 1.5 m. We recommend that these surveys be continued annually to provide ongoing estimates of abundance for future assessment work and to inform conservation efforts focused on the survival or recovery of this species.