Assessing the influence of different inland lake management strategies on human-mediated invasive species spread

Species introduced to the Great Lakes region through shipping, pet and nursery trade, and as biological control have caused significant environmental damages and have increased the direct and indirect costs to boat owners and various water-dependent industries. Once established, recreational boating becomes the primary vector of spread for some of these species, such as zebra mussels (Dreissena polymorpha Pallas, 1771). Prevention and mitigation efforts in the past have focused on boater education, boat washing stations, and inspections; yet these management actions can be expensive with limited or largely unknown effectiveness. In this study, we used a gravity model framework to accurately simulate the spread of an aquatic invasive species. After parameterization, the constructed model effectively simulated the human-mediated movements of the historical dreissenid spread patterns, correctly predicting an average accuracy of 78.2% (standard deviation = 0.01%) lakes invaded per model run. We then used the model to determine the effectiveness of three different invasive species management scenarios in Michigan: deterring boaters from lakes with a high likelihood of invasion, targeted education at high-risk lakes, and a large-scale education effort. Results indicated that deterring boaters from high-risk lakes is effective in the first five years of an invasion, targeted education is more effective at late stages of an invasion, and large-scale education is effective at all stages of an invasion. Our results indicate that managers should be flexible in their management actions and that different strategies are likely more effective at different stages of an invasion.