Largemouth Bass Range Expansion in Northern Minnesota

Northeastern Minnesota is at the northern edge of the Largemouth Bass Micropterus dolomieu range.  Short growing seasons and low productivity are cited as reasons the warmwater species does not flourish in this part of North America.  Lake management surveys have captured the species more frequently over recent decades and previously unknown populations are being discovered.  The specific cause(s) of the increase and its effect on other fish are unknown.  We hypothesize the cause of this range expansion is increased recruitment of juvenile Largemouth Bass due to a longer growing season and increased aquatic vegetation allowing the young-of-the-year fish to grow to a larger size before entering their first winter. To test this hypothesis, we designed a study of lakes in northeastern Minnesota without Largemouth Bass, lakes with recently detected populations, and lakes with historical populations.  We will examine seasonal lake warming and aquatic vegetation abundance to determine thresholds most important in predicting population type. We will compare trophic position of key fish species to determine how the energetic pathways vary across population type.  Results of this study will help determine the vulnerability of other lakes to Largemouth Bass expansion and predict how that expansion will affect other game fish.