Are zebra mussels hitching a ride on your boat?

MAISRC researchers recently completed a project assessing the risk of zebra mussels spreading in the residual water left in boats after they’ve been drained. The first-of-its-kind study found that although veligers can be found in very small amounts of water, ballast tanks contained the largest number of zebra mussel veligers. The study also found that veligers can survive for a couple of days in residual water, emphasizing the importance of taking additional steps such as hot water decontamination when going between lakes.

The first phase of this project focused on assessing how many veligers could be found in the residual water of boats. Samples were collected from over 250 boats leaving Lake Minnetonka and Gull Lake. Samples were collected from hard and soft ballast tanks, sterndrive engines, live wells, foot wells, splash wells, bilges, and jets. Of these compartments, veligers were found in ballast samples 97% of the time. Veligers were found in 89% of sterndrive engines, meaning that these two compartments have the greatest likelihood of transporting veligers.

The second phase of this study included experimental mortality trials on veligers in two common boat compartments: live wells and ballast tanks. The lives wells were exposed to air temperatures of 20, 27, 32, and 38 °C; the ballast tanks were exposed to 20 and 32 °C. For veligers in the residual water of live wells, > 95% mortality was observed after five hours of exposure to all temperatures. The same level of mortality was reached in ballast tanks at 48 hours. This tells us that watercraft equipped with ballast tanks are at a greater risk of transporting live veligers to new water bodies over short trips.

Both aspects of this research tell us that extra steps -- such as hot water decontamination -- should be taken by boat owners to minimize the likelihood of introducing live veligers to new water bodies via overland transport. Providing on-site decontamination services can help reduce the risk of spreading invasive species. Additionally, the nationally recognized suggestions to dry your watercraft for five days or more (Stop Aquatic Hitchhikers!) drastically reduces the risk of transporting living zebra mussel veligers to new water bodies. It’s important to remember that veliger movement is one possible method for spread; it’s currently unknown how many veligers are needed to create a new zebra mussel infestation.  The movement of adults still remains a higher risk.

Going forward, members of this research team are working with the American Boat and Yacht Council to relay findings and discuss options for redesigning boats that could help limit the spread of AIS.

Learn more about this research in this Pioneer Press story or on our website. The full thesis, Occurrence and Survival of Zebra Mussel Veliger Larvae in Residual Water Transported by Recreational Watercraft, is available here. Thank you to the Brunswick Freshwater Boat Group, Brunswick Public Foundation, and Tonka Bay Marina for funding this research!

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