How invaded is our lakescape?: Enumerating invaded lakes in the Northern Highlands Lake District of Wisconsin

Background/Question/Methods

By advancing biotic homogenization, invasive species are threatening global biodiversity, causing economic impacts both local and global in scale. Freshwater ecosystems are particularly vulnerable. Despite the severity of this problem, we do not have sufficient data to answer simple questions like “how many lakes are invaded?” with useful precision.  In the Northern Highlands Lake District of Wisconsin, USA, a region whose economy is largely driven by lake-associated recreation, we conducted a stratified random survey to determine how many and what types of lakes are invaded.  

Results/Conclusions

In the summers of 2010 and 2011, we sampled 88 lakes for seven aquatic invasive species (AIS) that make up the majority of known AIS populations in the region. The lakes studied ranged in accessibility to boaters, conductivity, and surface area.  Overall, 55 lakes harbored at least one AIS, although likelihood of being invaded significantly differed among lake types.  For instance, all lakes with boat launches and high conductivity had at least one AIS, while lakes that were undeveloped and away from roads were consistently uninvaded.  By extrapolating our results across the region, we conservatively estimate that at least ~900 lakes (about 30%) in the region are invaded.  For comparison, only about 1,000 (6.7%) lakes in the entire state have documented invasions. Our results demonstrate the dramatic extent at which biological invasion is occurring across our landscape and highlight the need for comprehensive prevention and control efforts.