Abstract
Disturbance from whale-watching can cause significant behavioural changes with fitness consequences for targeted whale populations. However, the sensory stimuli triggering these responses are unknown, preventing effective mitigation. Here, we test the hypothesis that vessel noise level is a driver of disturbance, using humpback whales (Megaptera novaeangliae) as a model species. We conducted controlled exposure experiments (n = 42) on resting mother-calf pairs on a resting ground off Australia, by simulating whale-watch scenarios with a research vessel (range 100 m, speed 1.5 knts) playing back vessel noise at control/low (124/148 dB), medium (160 dB) or high (172 dB) low frequency-weighted source levels (re 1 μPa RMS@1 m). Compared to control/low treatments, during high noise playbacks the mother's proportion of time resting decreased by 30%, respiration rate doubled and swim speed increased by 37%. We therefore conclude that vessel noise is an adequate driver of behavioural disturbance in whales and that regulations to mitigate the impact of whale-watching should include noise emission standards.
Highlights
Whale-watching comprises the largest component of marine mammal-based tourism, and the multibillion-dollar industry is increasing globally (Hoyt, 2018)
Within control/low noise treatments, the maximum low frequency (LF)-weighted Received levels (RLs) of vessel noise was 112 ± 1 dB re 1 mPa RMS, which was close to the ambient noise levels in Exmouth Gulf
With a maximum LF-weighted of RL 133 ± 2 dB re 1 mPa RMS, the mother’s behaviour was significantly affected from before to during vessel approaches as her amount of time resting decreased by 27%, respiration rate increased by 35% and swim speed increased by 33%
Summary
Whale-watching comprises the largest component of marine mammal-based tourism, and the multibillion-dollar industry is increasing globally (Hoyt, 2018). The most common form of whale-watching is boat-based, where tours often repeatedly target specific cetacean populations in accessible coastal waters. Commercial whale-watching began in 1955 and has previously been viewed as a non-invasive activity that can generate a revenue for local economies as an alternative to whaling whilst allowing depleted whale stocks to recover. It is, increasingly clear that boat-based whale-watching can have short-term behavioural impacts on individuals (New et al, 2015). While whale-watching has been shown to have both shortand long-term negative effects on cetaceans, the sensory drivers that elicit these behavioural responses remain unclear, preventing informed mitigation
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