Northern Minnesota river holds three state-listed mussels
 
Hove, M., S. Strong, A. Jacobson, J. Schussler, and V. Kurth. 1997. Triannual Unionid Report. Report No. 13, p. 22.
Univ. of Minnesota, 1980 Folwell Ave., St. Paul, MN 55108
(612) 624-3019, (note new) email address: Mark.Hove@fw.umn.edu
The mussel assemblage of the Lake of the Woods watershed in northern Minnesota is among the least studied unionoid faunas in the state (Graf 1997). The Big Fork River, a subdrainage in the watershed, flows north over rolling moraines, across the flat bed of Glacial Lake Agassiz, to the Rainy River; Minnesota's border with Canada. Much of the Big Fork River watershed is relatively pristine. Most of the land is covered by second growth aspen and pine forests, and a small number of ranches (Waters 1977).

Twenty-five sites were surveyed in the Big Fork River basin. Lampsilis siliquoidea, Pyganodon grandis, and L. cardium were regularly found throughout the watershed. Lasmigona compressa was found in the lower two-thirds of the basin. Utterbackia imbecillis, Anodontoides ferussacianus, Lasmigona complanata, Strophitus undulatus, and Ligumia recta had scattered distributions. L. costata was represented by a single valve from a headwater tributary. Lasmigona compressa, L. costata, and Ligumia recta are listed as special concern species in Minnesota. Mussel densities ranged between 0-32 mussels/m2 (Figure 1).

 
 
Figure 1. Mussel densities in the Big Fork River, Minnesota.

During the survey we observed an interesting color variant of Ligumia recta. Most L. recta in the St. Croix and upper Mississippi rivers have gray and black mantles with white-tipped papillae. However, two displaying L. recta in the Big Fork River had a much lighter, yellow-gray mantle. These mussels, like other brooding L. recta we've witnessed, were lying out on top of the river bed occasionally waving their mantles.

This survey was made possible with support from: the Legislative Comm. on Minnesota Resources, Chantel Cook and Richard Buech of the National Park Service, Jay Hatch, Joanne Iskerka, Cindy Lee, and Susan Weller of the Bell Museum of Natural History, Dan Hornbach of Macalester College, and Anne Kapuscinski of the University of Minnesota.
 

Graf, D. L. 1997. Distribution of unionoid (Bivalvia) faunas in Minnesota, USA. The Nautilus 110(2): 45-54.

Waters, T. F. 1977. The streams and rivers of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 373 pp.