Evidence-Based Decision Making to Underpin the Thresholds in New Zealand's Craft Risk Management Standard: Biofouling on Vessels Arriving to New Zealand

Vessel biofouling is a significant pathway for the introduction of nonindigenous marine species (NIMS). New Zealand is the first nation to regulate the vessel biofouling pathway, with controls scheduled to come into force in May 2018. The Craft Risk Management Standard (CRMS): Biofouling on Vessels Arriving to New Zealand specifies the hull fouling thresholds that vessels must meet; and here, we present the evidence-based decisions that underpin these thresholds. Under the CRMS, a vessel must arrive in New Zealand with a "clean hull," the thresholds for which are governed by the intended duration of a vessel's stay in New Zealand. For example, long-stay (>= 21 days) vessels must meet a more stringent standard of hull cleanliness due to the increased likelihood of release and establishment of NIMS. While setting a clean hull threshold at "slime layer only" can be tractable when vessels operate within the specifications of antifouling coatings, incidental amounts of macrofouling can establish even under the best management practices. Because of such instances, the thresholds within the CRMS were designed to allow for the presence of some macrofouling species, albeit with restrictions to minimize biosecurity risk. These thresholds are intended to limit species richness and to prevent successful reproduction and settlement of the allowed taxonomic groups while considering the practicality and feasibility of implementation. The difficulties of managing biofouling on different areas of the hull are acknowledged within these thresholds. For example, a greater tolerance of macrofouling has been allowed for niche areas due to the difficulties in preventing biofouling on these areas.