. The Canadian field-naturalist. 1991 Notes 401. Figure 1. Major drainages in Minnesota. The Mississippi River drainage below St. Anthony Falls includes the Minnesota and St. Croix river drainages. The question mark (?) indicates the approximate loca- tion for the only published record of Necturus mac- ulosus from above St. Anthony Falls (Breckenridge 1944); its occurrence has been documented in each of the other drainages (Oldfield and Moriarty, in preparation). Also shown are the former locations of glacial lakes Aitkin and Upham, with inlets and outlets, as discussed in the text. Map modifi
. The Canadian field-naturalist. 1991 Notes 401. Figure 1. Major drainages in Minnesota. The Mississippi River drainage below St. Anthony Falls includes the Minnesota and St. Croix river drainages. The question mark (?) indicates the approximate loca- tion for the only published record of Necturus mac- ulosus from above St. Anthony Falls (Breckenridge 1944); its occurrence has been documented in each of the other drainages (Oldfield and Moriarty, in preparation). Also shown are the former locations of glacial lakes Aitkin and Upham, with inlets and outlets, as discussed in the text. Map modified from those provided by Underhill (1957), Hobbs (1983), and Oldfield and Moriarty {in preparation). lar power plants, Monticello and Sherco, (Sharon Sarappo, Northern States Power Company biologist, personal communication), located along a portion of the Mississippi River above St. Anthony Falls with apparently optimum habitat (abundant boulders and rubble). Whether or not N. maculosus is present in the Mississippi drainage above St. Anthony Falls, it is possible to explain its distribution in Minnesota on the basis of fish dispersal routes proposed by Underhill (1957). Temporary access to the Mississippi drainage above St. Anthony Falls was provided by the Grantsburg sublobe, an extension of glacial ice that diverted the Mississippi River around the subsequent location of St. Anthony Falls through what would become the Lower St. Croix Valley. Access to the Hudson Bay drainage was provided by drainage from glacial Lake Agassiz through the glacial River Warren, following the course of the present Minnesota River. Access to the Lake Superior drainage was available through several routes at various times, but most directly through the present day Brule and St. Croix river valleys. Barring the possibility of extinction subsequent to colonization, absence from one drainage of aquatic species present in other drainages suggests that access to that drainage was blocked before closur
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