Effects of Whole-Lake Mixing on the Diet of Rainbow Smelt (Osmerus mordax)

Abstract

Rainbow smelt, an invasive coldwater fish species native to the eastern coastal US, were intentionally introduced into the Laurentian Great Lakes Region in the early 1900s to serve as forage for predatory fishes. Rainbow smelt reduce populations of native fish in the systems they invade. To eradicate invasive cold-water rainbow smelt in Crystal Lake, the lake underwent whole-lake mixing. The manipulation successfully created isothermic conditions and removed all coldwater habitat required by rainbow smelt. Although the induced mortality rate was significant (90%), the mixing did not eradicate rainbow smelt from Crystal Lake. For my research I hypothesized that a shift in diet may have helped the rainbow smelt population persist during the thermal manipulation. The mixing event removed the coldwater habitat, thereby inducing a spatial shift of rainbow smelt in an attempt to find new habitat. This movement could have changed the prey availability and prey selection, and those that were able to adapt to that change survived. There was evidence that rainbow smelt diet was effected by whole-lake mixing. Overall, the proportion of general zooplankton decreased during mixing and returned to a high proportion after mixing. The proportion of larger diet items increased during mixing. These finding may have future implications for management strategies.