Influence of vessel disturbance on Pacific harbour porpoise (<i>Phocoena phocoena vomerina</i>) echolocation

Vessel disturbance is one of many anthropogenic threats that are negatively impacting coastal cetacean populations worldwide. Noise pollution from vessels can cause varying levels of disturbance in cetaceans, depending on several factors such as vessel type and speed. Pacific harbour porpoises (Phocoena phocoena vomerina) are distributed throughout coastal waters of the North Pacific Ocean, with large aggregations observed near the entrance to the Port of Prince Rupert in British Columbia, Canada. This area serves as an important year-round foraging ground for harbour porpoises. However, it is also one of the fastest growing container ports in North America, with planned increases in activity. Harbour porpoises are highly sensitive to vessel-related acoustic disturbances, but the effects of vessel activity on their foraging rates remain unclear. In this study, we used a combination of land-based surveys, passive acoustic monitoring (PAM) devices (C-PODs and F-PODs), and automatic identification system (AIS) data to investigate the relationship between vessel activity and harbour porpoise echolocation activity-both foraging and non-foraging-in the heavily trafficked Chatham Sound, adjacent to the Port. Our results show that an increase in the total number of vessels negatively affected both foraging and non-foraging echolocation activity, with less echolocation observed in the presence of more ferries and tugs. Similarly, vessels traveling at higher speeds (>6 m/s kn) had a negative effect on echolocation activity. Tugboats and passenger vessels, in particular, had a wider range of effects on all harbour porpoise echolocation activity. Our findings indicate that implementing a vessel slowdown (~5 m/s) along the approach to the Port of Prince Rupert would reduce disturbances to harbour porpoises and likely benefit other coexisting species that rely on quiet oceans for communication and foraging.