Doolittle, T.C.J. 1988. Distribution and relative abundance of freshwater mussels in the Saint Croix National Scenic Riverway. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resources. Unpaged.
Mussel distribution and relative abundance along the 250 mile Saint Croix National Scenic Riverway were determined by sampling 84 regularly distributed sites. Sampling took place in the summer of 1987 and utilized SCUBA techniques. Each sample site encompassed 60 square meters of river bottom. Thirty-five midden pile sites were sampled as well. Thirty-eight species were found on the entire Riverway (2 species represented by dead material only). Thirty-five species were found alive and 2 species were represented by dead shells only in the Saint Croix River. Sixteen species, all alive, were found in the Namekagon River. Range extensions were documented for Cumberlandia monodonta, Simpsonaias ambigua, Quadrula fragosa, Truncilla truncata, Epioblasma triquetra, Truncilla donaciformis, Tritogonia verrucosa, Quadrula metanevra, Lampsilis higginsi, Elliptio crassidens, and Ellipsaria lineolata. Eight river stretches or sites were preliminarily identified as having significant mussel diversity or concentrations of rare species which merit special conservation attention. A clustered distribution pattern of mussels was apparent throughout the riverway. Two species associations were apparent and included primarily common species or primarily uncommon species. Areas containing the highest species diversity also had the rarer species, but these areas were not necessarily areas of high mussel densities. Most (96.4%) mussels were collected at depths between 0.5 to 3.5 m., this data being influenced by river levels. Over half (64.2%) of all the mussels collected occurred in sand, gravel, and rock bottom substrate of varying combinations.