Quantifying the effectiveness of three aquatic invasive species prevention methods

Efforts to prevent the spread of aquatic invasive species (AIS) have been widely implemented to mitigate economic and environmental harms. Boater education, watercraft inspection, and hot water decontamination are popular strategies for preventing AIS spread through recreational boating. However, few studies have quantified the effectiveness of these strategies under field conditions. We estimated the effectiveness of AIS preventions based on the performances of boaters, watercraft inspectors, and hot water decontaminators. Participants (n = 144) were recruited at public water access sites in Minnesota (n = 56) and Wisconsin (n = 1). Each participant was asked to inspect and remove AIS from a boat consistently staged with macrophytes in the same six locations, adult zebra mussels in two locations, spiny water flea in one location, and residual water in one location. The types and amounts of AIS removed were used to estimate the effectiveness of each prevention method. We observed that removal rates varied by type of AIS and location - the locations with macrophytes were most commonly removed by all participant types. There were also regional (within or outside of the Minneapolis/Saint Paul metro area) differences for some species, such as spiny water flea, perhaps due to regionally specific outreach campaigns. Hot water decontamination had the highest percentage of intervention effectiveness (mean = 84.4%), but was not significantly better than watercraft inspection (mean = 79.2%). Our results suggest boaters are less effective (mean = 56.4%) at removing AIS than both trained professional groups in this study, but nevertheless play an important role in AIS prevention. Furthermore, we identified areas of the boat that were often overlooked (e.g., winch, bow line, transducer) by boaters and could be incorporated into future outreach campaigns. We observed high variability in the actions (i.e., time spent, places looked, methods used) taken among individuals from each participant group, revealing opportunities for standardizing outreach and professional training to maximize effectiveness. This was particularly evident among decontaminators, who often made risk-based decisions to modify the protocol and relied on equipment that often failed to reach minimum temperature thresholds for lethal exposure. This study can better inform AIS managers as they weigh the cost-benefit of each prevention strategy to meet their management objectives.