Optimising voyages for biodiversity: rerouting vessels around ocean giants can have minimal impact on shipping

Ship strikes are a significant and growing threat to marine megafauna, yet few mitigation measures are implemented at scale due to perceived economic costs to shipping. Here, we present a proof of concept for integrating biodiversity considerations into commercial voyage optimisation, using priority aggregation sites for the endangered whale shark (Rhincodon typus) as a case study. We simulated eight port-to-port voyages for two vessel classes--a crude oil tanker and a container ship--under three routing scenarios: baseline optimisation, speed reduction to 10 kts within core habitats, and complete avoidance of these areas. Across routes, fuel-use changes ranged from -0.13% to 9.65%, with minimal impacts (<1%) for most long-distance voyages. Results indicate that speed reduction is the more efficient mitigation for short voyages, while area avoidance is preferable for longer voyages, with impacts varying by vessel type and operational constraints. Incorporating dynamic, species-specific habitat layers into voyage planning could enable targeted ship-strike mitigation with negligible disruption to global trade. Adoption of such measures - supported by improved data pipelines, real-time forecasting, and integration into regulatory and incentive frameworks - offers a scalable pathway to align biodiversity conservation with decarbonisation goals in the maritime sector.