Assessing vessel slowdown for reducing auditory masking for marine mammals and fish of the western Canadian Arctic.

Abstract Vessel slowdown may be an alternative mitigation option in regions where re-routing shipping corridors to avoid important marine mammal habitat is not possible. We investigated the potential relief in masking in marine mammals and fish from a 10 knot speed reduction of container and cruise ships. The mitigation effect from slower vessels was not equal between ambient sound conditions, species or vessel-type. Under quiet ambient conditions, a speed reduction from 25 to 15 knots resulted in smaller listening space reductions by 16–23%, 10–18%, 1–2%, 5–8% and 8% respectively for belugas, bowheads, bearded seals, ringed seals, and fish, depending on vessel-type. However, under noisy conditions, those savings were between 9 and 19% more, depending on the species. This was due to the differences in species' hearing sensitivities and the low ambient sound levels measured in the study region. Vessel slowdown could be an effective mitigation strategy for reducing masking. Graphical abstract Unlabelled Image Highlights • The relief in masking from a 10 knot vessel speed reduction was investigated. • Listening space was reduced most for seals, then whales and fish near the vessel. • Slowing vessels by 10 knots gave the most masking relief under noisy conditions. • Variance in masking relief was due to frequency-dependent hearing between species. • Vessel slowdown could be a viable mitigation option when re-routing cannot be done. [ABSTRACT FROM AUTHOR]