The decline of freshwater molluscs in southern Manitoba

A survey of freshwater molluscs was conducted in southern Manitoba in 1998 and was compared with a similar survey from 1975-1978. Sites were classified according to main type of human impact: crops, livestock, logging, recreation, mining, hydro and minimal impact. All development categories increased at the expense of minimal impact sites. Frequencies of freshwater mussels and most gastropods declined, and some species recorded in the earlier survey were not found in 1998. Mean species richness of gastropod communities decreased at all site categories. The lowest richness was consistently observed at sires affected by mining and intensive livestock production. Small gastropod species appeared to show the most precipitous declines.