Commercial vessel arrivals and wetted surface area: an exploration of non-indigenous species invasion likelihood in coastal Alaska

High latitudes are at the leading edge of biological invasions, and commercial shipping, a widely available mechanism for transporting non-indigenous species (NIS), presents a multi-faceted and novel risk to port systems experiencing increasing vessel traffic. This study uses vector analysis, a foundational aspect of regional biosecurity evaluation, to explore the relative likelihood of commercial vessels introducing non-indigenous species via biofouling for six vessel types (bulk carrier, container, passenger, tanker, roll-on roll-off, and general cargo) arriving in Alaska ports between 2012 and 2022 by assessing variability among four risk factors. We integrated publicly available datasets to comprehensively assess spatial and temporal trends in commercial vessel traffic and examined characteristics of vessel size and behavior that influence likelihood of NIS introduction. These factors include wetted surface area (WSA) of a vessel which quantifies potential vessel-specific habitat available to biofouling organisms based on gross tonnage and vessel-type niche proportion providing a measure to quantify the likelihood of introduction to a particular location and time. Additional risk factors considered in this analysis include the following vessel behaviors that can modify invasion likelihood: hull cleaning, environmental similarity between origin and arrival port, and residency time in arrival port. Nearly 30, 000 commercial vessel arrivals delivered 430 kilometers 2 of wetted surface area during the study period, comprised largely of passenger vessels calling at ports in southeast Alaska followed by tankers in southcentral Alaska. Overall, arrivals grew 23% and WSA grew 50% between 2012 and 2022, driven primarily by increasing large passenger vessel traffic, while other vessel types remained steady. Notably, arrival type and risk factors varied regionally and were strongly influenced by economic drivers and global phenomena such as the COVID-19 pandemic. These findings demonstrate that biofouling has ample potential as a marine NIS vector in Alaska by refining regional and local potential for vessel biofouling and providing critical context for proactive management and regional biosecurity at high latitudes. The methods employed here can be applied to other at-risk port systems to strengthen place-based understanding of biofouling risk and invasion potential.