FACTORS INFLUENCING THE DISTRIBUTION AND ABUNDANCE OFF THE ENDANGEREDWINGED MAPLELEAF MUSSEL QUADRULA-FRAGOSA IN THE ST-CROIX RIVER, MINNESOTA AND WISCONSIN

We examined physical and biological factors that mac influence the dis tribution of the endangered winged mapleleaf mussel Quadrula fragosa ( Conrad, 1835). Quantitative sampling of the mussel community was under taken at two sites in the St. Croix River known to harbor Q. fragosa. Additional searches were conducted specifically for Q. fragosa individ uals. For each quantitative sample of mussels, substrate composition, water velocity and depth were assessed and mussels were identified and measured, In general, Q. fragosa does not have habitat requirements d ifferent from the rest of the mussel community, although Q. fragosa oc curred in shallower areas with lower bottom current velocity compared to the overall mussel community. There was no difference in substrate composition in areas with and without Q. fragosa. Mussel community den sity and richness were higher in areas where Q. fragosa was found. The mussel community associated with Q. fragosa was not significantly dif ferent from the general mussel community in the area. However three sp ecies (Truncilla truncata, Truncilla donaciformis and Quadrula metanev ra) were significantly associated with Q. fragosa. Due to its associat ion with dense and diverse mussel communities, management that benefit s the entire mussel community should be effective in protecting this e ndangered species.