Whale-watching, including swim-with-whales activities, is developing at an enormous rate in Reunion Island. This is raising concerns about its impacts on breeding humpback whales and challenging the sustainability of the activity. In 2017, a dedicated at sea patrol team, “Quietude” was created to observe, monitor and sensitize whale watchers at sea in order to improve compliance with local guidelines. In this context, the team assessed whale-watching in Reunion Island during two humpback whale breeding seasons in 2017 and 2018, between June and October. Sighted groups were mostly composed of mother/calf pairs spending most of their time resting near or at the surface. Whale-watching vessels were present in 85.1% of sightings, of which 68.4% were recreative. Swim-with-cetaceans activities were very frequently observed in 42% of sightings. Overall, compliance with the charter was as high as 68% of whale sightings with vessels/swimmers were in line with the recommendations. However, low compliance (32.8%) was observed with the specific recommendations of swim-with-cetaceans activities. Swimmers were reported in active groups displaying agonistic behaviors, which poses evident human safety concerns. Humpback whale resting and nursing behaviors were disrupted significantly by whale-watching activities. Humpback whales tended to avoid vessels and swimmers, especially when their behavior was intrusive or not compliant with the charter. Positive humpback whale responses were more likely to occur if the charter’s recommendations were not breached. Our results highlight how a non-binding regulation, with recommendations scrupulously pursued, allows for a reduction in whale-watching disturbances and supports a better tourism experience. Our results advocate for reinforcing tourism education, whale-watching adaptive management and regulations, specifically for vulnerable groups with a calf and for the swim-with-whales activities. This could be efficiently achieved by engaging all stakeholders and the permanent team on the field “Quietude” to enhance dissemination of best practices and sensitivity around sustainable values of implemented regulations.

The effect of nature-based tourism on wildlife has been the focus of much attention. Studies have demonstrated how boat-based cetacean-watching tourism can cause both short-term and long-term effects on targeted populations. However, limited attention has been given to the effect of swim-with activities on humpback whales (Megaptera novaeangliae). This study was to quantify whale responses to swim-with activities off Reunion Island during the 2018 humpback whales breeding season. We used both under-and above-water videos collected from social media outlets, commercial whale-watching operators and audiovisual professionals. We documented a high rate of agonistic whale behaviors (during 42.1% of all observations (n=164)) towards swimmers within videos containing swim-with events. We documented seven agonistic behaviors including threat, attack or defense behaviors that were predominantly exhibited by mother/calf groups (73.8%; n=121) and on singletons (16.5%; n=27). Pectoral shears (27.4%) and fluke trashes (23.2%) were the most exhibited agonistic whale behaviors aimed towards swimmers, both of which pose a danger and serious injury to swimmers. During swim-with attempts whales changed their behavioral state (82.3%, n=159) and used avoidance tactics to avoid swimmers (56.1%, n=92). Whales exhibited a higher rate of agonistic behaviors when swim groups were active and dispersed, in contrast to when they were quiet and compact. To mitigate whale disturbance and improve swimmer safety, we recommend avoiding swimming with whale groups containing a calf. Our findings support the implementation of strong regulations and educational tools to ensure a sustainable practice of whale watching off the Reunion Island.

Marine wildlife tourism has rapidly developed in Reunion Island, due to a large demand for interactions with a resident population of spinner dolphins (Stenella longirostris). The presence of dolphin-watching vessels close to dolphin groups can cause short-term impacts on their behaviour; cumulative incidences likely result in deleterious long-term impacts on the population. Using scan sampling, we collected behavioural data on spinner dolphins to evaluate the short-term effects of dolphin watching on their behaviour. The dolphins were less likely to begin socialising or diving while travelling and more likely to stay travelling and milling in the presence of vessels. Additionally, activity budgets for resting and socialising decreased simultaneously with increased travelling and milling. Avoidance responses significantly increased with an increase in the number of vessels and non-compliance with the local dolphin-watching guidelines. These behavioural responses are likely to have energetic costs for the dolphins, which may lead to decreased survival and reproductive success at individual and population levels. More restrictive regulations, increased surveillance and animal-based measures are key tools to adapt the conservation efforts in Reunion Island. Further studies on the island’s resident dolphin populations are necessary to ensure the continuity of dolphin-watching activities in a sustainable manner.