Reducing whale-vessel strikes through multiobjective vessel traffic routing

Vessel strikes threaten many large whale species. Managers employ several mitigation measures to reduce vessel strike risk, including establishing or modifying vessel routing measures, such as shipping lanes. However, most studies utilized to inform the configuration of shipping lanes only consider a limited number of potential lanes, and in many cases, the criteria used to generate the lanes are unclear. We developed an approach to design, modify, or evaluate shipping lanes that involves clearly defining the objectives of the lanes and using the k least-cost path (KLCP) algorithm, which identifies the KLCPs between two points on a cost surface, to identify all lanes that meet the objectives. We applied our approach to evaluate recommended shipping lanes in Cape Cod Bay, Massachusetts (United States), and off the Atlantic Coast of the southeastern United States with respect to the risk of vessel strikes to North Atlantic right whales (Eubalaena glacialis) and the time it takes vessels to travel the lanes. We identified all lanes with a risk of right whale strikes and a travel time less than or equal to that of the recommended lanes using the KLCP algorithm. In most cases, the lanes identified had similar spatial configurations to the recommended lanes and reduced the risk of strikes by <15%, which indicates that the existing recommended lanes are adequately, but not optimally, designed to reduce strike risk and travel time relative to potential alternative lanes. Our approach applying the KLCP algorithm provides a thorough, objective, and transparent way to identify vessel routing configurations that minimize whale-vessel strikes and meet other objectives.