Recreational watercraft decontamination: can current recommendations reduce aquatic invasive species spread?

Decontaminating recreational watercraft, and fishing, sailing or watersports equipment after use can reduce the overland dispersal of aquatic invasive species (AIS) among lakes. Recommended methods include pressure-washing, rinsing with hot water, using cleaning agents, or air-drying, but the extent of their efficacy is unknown. The aim of this review is to assess the effectiveness of current decontamination measures for recreational watercraft against various AIS. Web of Science, Greenfile, Environment Complete and Geobase were searched for articles published through September 2019. Studies on preventing overland AIS spread, and plant and invertebrate AIS response to hot water, pressure-washing, desiccation or cleaning agents, were selected. Of 37 studies included in the review, the majority (70.3%) assessed air-drying, followed by hot water (32.4%), household chemicals (16.2%), and pressure-washing (2.7%). The recommended air-drying duration of up to one week produced high mortality (≥ 90%) among several invertebrate and macrophyte species, although survival was high for certain aquatic snails. Larger and/or older invertebrates were more resistant to desiccation. Aquatic plant survival and growth were inversely related to water loss (a function of drying time and relative humidity), and short or single fragments were less resistant to air-drying than larger or clustered fragments. Immersion in water ≥ 50 °C for 15 minutes resulted in 100% mortality among mussels, small invertebrates and some plant species. A higher temperature of 60 °C was required for hot water spray applications lasting ≥ 5 seconds to achieve the same mortality rate among dreissenid mussels. High pressure-washing eliminated significantly more entangled plants, and small organisms and seeds than low pressure. Household chemicals such as salt or bleach required specific doses and immersion durations to be lethal to small organisms. This review reveals that current decontamination methods may be effective, but their efficacy against a diversity of AIS, including those on watch lists, are not yet well-understood. As the literature is currently skewed towards studies on air-drying, which has limited efficacy, further research is required to evaluate practical, and alternate or combined measures to best inform management practices.