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.
Highlights
Vessel noise is a primary driver of behavioural disturbance in cetaceans, which are targeted during whale-watch activities
An increase in the presence of whale-watch vessels was related to a decrease in the relative abundance of bottlenose dolphins (Tursiops aduncus) in Shark Bay, A ustralia[7], while in Doubtful Sound, New Zealand, there was an overall decrease in population size of bottlenose dolphins (T. truncatus)[8]
Since current whale-watching guidelines assume that physical proximity is the primary driver of disturbance of c etaceans[27], a quiet vessel is assumed to have the same impact with that of a very noisy vessel which is at the same distance, angle of approach and speed
Summary
Vessel noise is a primary driver of behavioural disturbance in cetaceans, which are targeted during whale-watch activities. 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. To facilitate the sustainability of the whale-watching industry and to support the development of best practice guidelines based on noise level, we tested 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 louder noise emissions. During experiments with a hybrid whale-watch vessel, the quieter electric engines were used and behavioural responses of the pilot whales were compared to when the same vessel approached with the louder petrol engines in use. Experiments were conducted in a deep-water environment off the Canary Islands, where ambient noise levels are low, and the noise emission levels of whale-watch vessels are audible to the whales
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