Decreased resting and nursing in short-finned pilot whales when exposed to louder petrol engine noise of a hybrid whale-watch vessel

Abstract

Vessel noise is a primary driver of behavioural disturbance in cetaceans, which are targeted during whale‑watch activities. Despite the growing, global effort for implementing best‑practice principles, to date, there are no regulations on whale‑watch vessel noise levels. Here, we test the hypothesis that a whale‑watch vessel with a low noise emission will not elicit short‑term behavioural responses in toothed whales compared to a vessel with a louder engine. We measured behavioural responses (n = 36) of short‑finned pilot whales (Globicephala macrorhynchus) to whale‑watch vessel approaches (range 60 m, speed 1.5 kn). Treatment approaches with a quieter electric engine (136–140 dB) compared to the same vessel with a louder petrol engine (151–139 dB) (low‑frequency–mid‑frequency weighted source levels, re 1 µPa RMS @ 1 m) were examined. Focal whales were resting mother and calves in small group sizes. During petrol engine treatments, the mother’s mean resting time decreased by 29% compared to the control (GLM, p = 0.009). The mean proportion of time nursing for the calf was significantly influenced by petrol engine vessel passes, with a 81% decrease compared to the control (GLM, p = 0.01). There were no significant effects on behaviour from the quieter electric engine. Thus, to minimise disturbance on the activity budget of pilot whales, whale‑watch vessels would ideally have source levels as low as possible, below 150 dB re 1 µPa RMS @ 1 m and perceived above ambient noise.