Whale-watching of cetaceans (whales, dolphins and porpoises) is a growing, multi-billion-dollar tourism industry. It has been considered a non-invasive alternative to commercial whaling, but it can however lead to short- and long-term behavioural impacts with severe fitness consequences for targeted populations. Despite the growing evidence for negative short- and long-term effects from whale-watching, the sensory stimuli from whale-watch boats that trigger these impacts are still unknown, hampering effective mitigation. Previous studies have focused on the physical proximity of whale-watch boats to cetaceans. Thus, current whale-watching guidelines rest on the premise that physical proximity is the primary driver of disturbance, and stipulate approach distance (typically around 100 m), angle (typically from the rear and side), and speed limits (typically below wake speed). However, underwater noise from boats is of concern as sound propagates well in water and hearing is the primary sensory modality of cetaceans, yet there are no tests of whether noise level is a driver of behavioural responses induced by whale-watching boats.
This project sought to test the hypothesis that underwater noise from whale-watch boats is a stimulus that elicits short-term behavioural responses in cetaceans. To do this, the researchers measured behavioural responses of whales to different boat noise levels during controlled exposure experiments. The humpback whale (Megaptera novaeangliae) was used as a model species, it being the most targeted species in the whale-watch industry. The study resulted in a large sample size for controlled exposure experiments examining boat noise. The study showed for the first time that underwater boat noise level is indeed a driver of disturbance during whale-watching scenarios. The researchers also show that if sufficiently silent boats are used at 100 meters range from the whales, that there are no apparent behavioural effects. From these findings, it is recommended that the whale-watch industry use quiet boats (for example, boats with source levels less than 150 dB re 1 μPa RMS when operating around whales at guideline distances of 100 m). These recommendations will allow operators to approach cetaceans in a responsible, sustainable manner in a way that also offers eco-tourists a view of undisturbed wildlife. These findings provide a paradigm shift in how whale-watching should be regulated to make it sustainable for future generations.
