The freshwater mussel fauna (Bivalvia: Unionidae) of the Knife River, Minnesota, following a rotenone treatment

Abstract

In October 1989, the Minnesota Department of Natural Resources (MNDNR), treated the Knife River, its tributaries, and Knife Lake with rotenone to eliminate rough fish in the system. At the time of the treatment it was believed that the rotenone application would not have an adverse impact upon the mussel fauna. Therefore, a pre- and post-treatment survey of the mussel community was not immediately conducted. During 1999 the MNDNR initiated a statewide mussel survey program which included a mussel survey of the Knife River in 2000. Nine sites along the Knife River were surveyed by divers who collected over 900 live and dead mussels, including 17 live species. Catch per unit effort for live mussels was similar in the Knife River when compared to other streams in the same drainage. None of the collected mussel species was represented by dead shells only, indicating no species were lost. Individuals from several of the species were greater than 10 years of age, indicating that they were present prior to rotenone treatment. Mussels less than 10 years of age were also collected, indicating that successful reproduction has occurred since the rotenone application. These results suggest that the mussel species that inhabited the Knife River before the rotenone treatment are still present and comparatively similar in abundance to other streams throughout the drainage.