The zebra mussel, a non-indigenous species in North American freshwater ecosystems, has received significant attention over the past two decades as a costly and damaging invader. In the USA, federal-, state-, and local-level policies designed to control and/or prevent the spread of this species remain flawed, in that they do not everywhere account for (or enforce regulations over) all potential anthropogenic dispersal pathways. Ballast water discharge is well-known as an important vector in the dispersal of aquatic invasive species in general, but for the zebra mussel its effects as a source of transmission have rarely been investigated. This article uses simple econometric techniques to measure the relationship between zebra mussel invasion in US states and domestic commercial navigation. Coefficient estimates suggest that incoming waterborne shipments from invaded states are an important determinant of the level of zebra mussel invasion in the receiving state. In designing a comprehensive framework for combating the spread of zebra mussels across US freshwater ecosystems, policy-makers may need to more carefully consider the monitoring and treatment of commercial ships' ballast water discharges as potentially effective strategies.

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