The influence of invasive aquatic plant removal on diets of bluegill in Minnesota lakes

摘要

Invasive aquatic plants in U.S. lakes and reservoirs frequently require managers to implement plant control, yet little is known about how these management efforts alter habitat available to adult fish. We used a before-after, control-impact (BACI) design to study four Minnesota lakes (two treated lakes and two untreated control lakes) to evaluate the influence of plant management using herbicides (i.e., endothall/2,4-D) on diets of adult bluegill (Lepomis macrochirus Rafinesque) over the course of 4yr. We hypothesized that removing plants would result in an immediate increase of prey items available to bluegill reflected in an increase in total items in the bluegill diet, and that an increase in prey items would affect diet breadth. Invasive Eurasian watermilfoil, Myriophyllum spicatum L., was eliminated following herbicide treatment; however, native plants immediately expanded and plant overall abundance in the littoral zone was not reduced. We found no significant treatment effects on number ofprey items per stomach, stomach content mass, diet composition, or abundance of major diet groups. However, we found that diet breadth increased posttreatment in the fall season, as evidenced by a more even distribution of bluegill diet items in stomachcontents. Bluegill diet composition varied across years and lakes (primarily due to changes in Cladocera), but not due to treatment. We concluded that early seasonal application of herbicides resulted in an immediate shift from invasive aquatic plants to a diverse native community, which had minor effects on diets of bluegill.