A probabilistic framework for evaluating ship strike hazard and the effectiveness of vessel speed reduction policies

Abstract

Ship strikes to whales are a threat to the recovery of threatened and endangered whale species. In Washington state, humpback whale (Megaptera novaeangliae) presence and vessel traffic are both increasing within federally designated humpback whale critical habitat, increasing the potential for collisions to occur. I estimated ship strike hazard in Washington humpback whale critical habitat, as well as potential hazard reductions under a Vessel Speed Reduction (VSR) policy using a ship strike model I developed. This model takes a probabilistic approach to quantifying hazard in the region and is largely driven by vessel characteristics and behaviors. I also modified a probability of lethality (PLETH) equation fit to empirical ship strike data by applying biological constraints which have not been previously incorporated in other models. I found that Washington humpback whale critical habitat is highly hazardous to humpback whales, particularly within the Strait of Juan de Fuca. I estimated that hazard could be reduced under a voluntary VSR policy by 9 to 22% across compliance rates of 50, 75, and 100%.