Influences of policy and vessel behavior on the risk of ballast-borne marine species invasions in coastal Alaska

The risk of species invasions in coastal Alaska is increasing due to the continued growth of global shipping and the expansion of trans-arctic trade routes. Coastal Alaska receives about 14 million metric tons of ballast water annually from 49 global ecoregions, including several highly invaded port systems along the west coast of North America. This study reviews the history and drivers of ballast water management policy in the United States and the impacts of policy changes and vessel practices on the risk of ballast-borne species invasions to coastal Alaska. We assessed spatial and temporal trends in ballast water discharge and management practices of vessels arriving to Alaska as reported to the National Ballast Information Clearinghouse from 2005 -- 2012. Notably, the Environmental Protection Agency's 2008 Vessel General Permit (VGP) triggered a sharp increase in reporting and an apparent 440% increase in total volume of ballast discharged between 2008 and 2009 by requiring previously exempted management and record keeping practices by crude oil tankers involved in coastwise trade, the dominant vessel type to discharge ballast in the state of Alaska. A vector-based risk assessment of post-VGP ballast water discharge to the top 15 ports of Alaska by volume indicates that the port of Valdez is most at risk of invasion. Klawock and Tolstoi Bay are least at risk. This is the first study to assess the risk of ballast-borne marine invasive species throughout coastal Alaska.