Since their introduction, rainbow smelt have disrupted lake food webs by outcompeting, preying upon, and displacing native fish including yellow perch (Perca flavscens), walleye (Sander vitreus), and cisco (Coregonus artedi), while also reducing zooplankton populations. A new study, supported by the Midwest CASC, describes how researchers counteracted the damaging influence of rainbow smelt and changed the lakes back into thriving native habitats by using the Resist-Accept-Direct (RAD) climate adaptation framework to guide their intervention.  

Drawing upon previous research and observations, the researchers strategically timed their intervention with a vulnerable period of the rainbow smelt’s life cycle: just before ice-out in early spring when the fish move to shallow gravelly or sandy areas to spawn. With the fish clustered together in shallow water, the researchers were able to break the ice, deploy nets, and ultimately remove over 12,000 individuals over the study period. They also stocked the Northern Wisconsin lakes with native cisco. 

The results were striking. In one of the two lakes, the relative abundance of yellow perch increased by 556% and their density rose by 143% over the four-year study. In the second lake, the relative abundance of walleye rose by 26%. Meanwhile, rainbow smelt populations plummeted by over 85% in both lakes. 

In contrast, two reference lakes that did not undergo intervention showed no significant changes. One, dominated by cisco at the beginning of the study, remained unchanged, while the other, dominated by rainbow smelt at the beginning of the study, showed an increase in the invasive fish over the four-year monitoring period.  

This successful intervention highlights the power of actively guiding disrupted ecosystems to a desired state using the “Direct” approach of the RAD framework. The study also used “panarchy theory,” which describes ecosystems as dynamic systems that cycle through phases of stability, disturbance, recovery, and growth. By understanding where an ecosystem is in this cycle, the researchers could apply the most effective RAD intervention to restore biodiversity and ecological function. While the other two RAD approaches, “Resisting” undesirable changes or “Accepting” changes that are unavoidable, may be useful in other scenarios, the “Direct” approach proved effective in both Wisconsin lakes. 

This research highlights the value of adaptive, science-driven strategies to manage invasive species and climate change.