High rates of vessel noise disrupt foraging in wild harbour porpoises ( <i>Phocoena phocoena</i> )

TLDR

Shipping is the dominant anthropogenic noise source in the world’s oceans, yet little is known about vessel encounter rates, exposure levels, and behavioural reactions of cetaceans, many of which rely on sound for foraging, communication, and social interactions. We used animal‑borne acoustic tags to measure vessel noise exposure and foraging effort in seven harbour porpoises in highly trafficked coastal waters. Harbour porpoises experienced vessel noise 17–89 % of the time, and high‑level exposures (>96 dB re 1 µPa) triggered vigorous fluking, bottom diving, interrupted foraging, and cessation of echolocation, resulting in markedly fewer prey‑capture attempts and potentially long‑term fitness costs, indicating that shipping noise disrupts foraging in this high‑frequency‑hearing species and may threaten other toothed whales.

Abstract

Shipping is the dominant marine anthropogenic noise source in the world’s oceans, yet we know little about vessel encounter rates, exposure levels and behavioural reactions for cetaceans in the wild, many of which rely on sound for foraging, communication and social interactions. Here, we used animal-borne acoustic tags to measure vessel noise exposure and foraging efforts in seven harbour porpoises in highly trafficked coastal waters. Tagged porpoises encountered vessel noise 17-89% of the time and occasional high-noise levels coincided with vigorous fluking, bottom diving, interrupted foraging and even cessation of echolocation, leading to significantly fewer prey capture attempts at received levels greater than 96 dB re 1 µPa (16 kHz third-octave). If such exposures occur frequently, porpoises, which have high metabolic requirements, may be unable to compensate energetically with negative long-term fitness consequences. That shipping noise disrupts foraging in the high-frequency-hearing porpoise raises concerns that other toothed whale species may also be affected.