Predicting the spread of zebra mussels (Dreissena polymorpha) to inland waters using boater movement patterns

Exotic species introductions are one of the major threats to biodiversity worldwide. Exotic species can be conspicuous, and their spread is often correlated with human activity. The rapidity of the Dreissena invasion in North America and its economic impacts provide a unique opportunity to study the invasion process. Trailered boating traffic may be the most important vector for the transport of zebra mussels among unconnected bodies of water. Therefore, knowing the activity patterns of boaters should allow us to predict the explicit regional-scale pattern of geographic spread. We used the results of a large boating survey conducted by the Wisconsin Department of Natural Resources to estimate the volume of boating traffic between waters known to contain zebra mussels (Great Lakes) and inland Wisconsin waterbodies. We found, (1) the most probable source of zebra mussels entering Wisconsin is Lake Michigan, (2) the most probable destinations are in eastern Wisconsin, and (3) geographic proximity to a source population and overall boater use are poor predictors of probability of invasion. Attention to human activity patterns may help predict the spread of other invading taxa.