Predicting future non-indigenous biosecurity risk from marine vessel traffic in New Zealand

Non-indigenous species (NIS) are being introduced beyond their native ranges at increasing rates. The major vector in the spread of marine NIS has been identified as shipping via ballast water and hull fouling. As waters warm under climate change, the range of suitable habitat is expected to increase and move toward the poles. In this study, the risk of NIS invasion to ports in New Zealand was estimated by combining the likelihood of introduction and the likelihood of establishment. The likelihood of introduction was derived from a transport model developed using marine vessel movements from Automatic Identification Systems, the New Zealand Department of Conservation, and ferry and water taxi timetables. The likelihood of establishment was predicted using species distribution modelling approaches. Of the six environmental variables used in these models, the most important predictors were temperature, bathymetry and salinity. Across New Zealand, ports with the highest risk of invasion were Auckland and the Hauraki Gulf, followed by Wellington, Picton and Opua (Bay of Islands). The framework and predictions developed here will help enable New Zealand’s marine biosecurity community identify cost-effective management actions to minimise invasion risk.