Assessing the Effects of Whale-based Tourism in Vava’u, Kingdom of Tonga: Behavioural Responses of Humpback Whales to Vessel and Swimmer Approaches
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Vava’u, Kingdom of Tonga, is a well-established whale-watching destination in the South Pacific. Between July and October, the waters around the archipelago represent one of the major breeding grounds for Oceania humpback whales (Megaptera novaeangliae). The Tongan government allows in-water interactions with whales and tour operators strongly promote the practice of swimming with whales, targeting mother-calf pairs in particular. However, there is increasing evidence, derived from empirical research on swim-with-cetaceans tourism, that this kind of interaction affects cetacean behaviour and can have negative effects on the cetaceans involved. This study represents the first empirical assessment of humpback whales’ behavioural responses to the approach of vessels and swimmers in Vava’u. A large part of the data collection has been conducted using a lightweight Unmanned Aerial Vehicle (UAV) to observe interactions from an aerial perspective. Fifty-six surveys took place during the 2016 and 2017 whale breeding seasons aboard dedicated research and swim-with-whales vessels. Specifically, data collected included whales’ dive time, number of reorientation events, and respiration rates in the absence and in the presence of boats and swimmers. Additionally, aerial videos of whales’ behaviour and interactions with swimmers were recorded with the use of a Vertical Take-Off and Landing (VTOL) UAV flown at 30 metres altitude. Vessel approach type and swimmer distance to whales were also noted. The comparison between UAV data collection methods and standard boat-based observation highlights how the aerial perspective provided by the UAV allows for a more precise assessment of whales’ behavioural state. In particular, important intraspecific interactions, such as nurturing and socialising, were detected more frequently and accurately via UAV than by boat-based observations. Furthermore, the data collected showed no signs of behavioural responses from the whales to the UAV flying at an altitude of 30 metres. With regard to whales’ responses to vessels and swimmers, results indicate that the proportion of time spent diving in the presence of in-water tourism activities increased significantly for mother-calf pairs. While the average mother dive time increased three-fold in presence of swimmers, the calf dive time did not differ from control data when there were no swimmers in the water. That is, calves spent a significantly higher proportion of time at the surface than their mothers during in-water tourism activities. The data also indicated that calves significantly reduced their number of respirations. Avoidance responses and significant changes in time spent in different behavioural states were recorded as a response to the vessels and swimmers. For instance, mother-calf pairs had a decreased proportion of time spent nurturing while the time spent travelling increased when approached by swimmers. Other observations of the whales included an increase of agonistic behaviours directed towards swimmers, putting swimmers at risk of injury. Finally, extremely low levels of compliance to existing Tongan swim-with-whales regulations were documented. That is, the minimum resting period between interactions was frequently disregarded and consecutive swims from different tour operators (also referred to as queueing) was regularly observed. These findings should be carefully considered by Tongan stakeholders¬ and other governments of countries that allow in-water interactions between tourists and whales. Measures to reduce the risk of negative impacts on the targeted cetaceans, and the potential for life-threatening injuries to tourists, should be implemented.