Short-term behavioural responses of manta rays, Manta alfredi, to tourism interactions in Coral Bay, Western Australia

Over the past two decades snorkelling or diving with manta rays has become a highly sought after experience for tourists worldwide. The Coral Bay manta ray interaction industry has experienced significant growth since its inception in the early 1990s, and concerns have been raised in recent years regarding disturbance to the manta ray population, and behavioural changes due to tourist interactions. This study was a preliminary assessment of the effect of tourism interactions on Manta alfredi behaviour in Coral Bay, Western Australia. In order to identify behavioural responses or changes, the natural behaviours exhibited by manta rays in the waters of Coral Bay were identified and described, and in doing so this study was the first to describe in detail four distinct foraging behaviours that are yet to be explained in the published literature. A total of 91 manta ray interactions were observed over a four month period to determine the frequency, form and influencing factors of short-term behavioural responses to three separate elements of the tourist interactions: the interaction with the swim group, the tour vessel and the attempt at capturing an identification photo. Behavioural responses were exhibited by manta rays during 34.1 % of interactions with swim groups (n = 91), 15.5 % of interactions with tour vessels (n = 98), and 48.1 % of manta rays exhibited a response to photo identification attempts (n = 77). Several factors were found to influence the occurrence of a behavioural response including the initial behavioural state and age class of the manta ray, the amount of surface splash, the approach strategy of the tour operator or photographer, the duration of the interaction and whether or not it was the manta ray’s first interaction that day. Forms of behavioural responses ranged from immediate avoidance responses to changes in behavioural state, including the termination of feeding behaviours and departure from cleaning stations. Such responses have the potential to lead to biologically significant impacts on the population, including declines in abundance and habitat displacement. Further study is necessary to confirm these links; however as the manta ray tourism industry continues to expand, precautionary management intervention is recommended. Responses to a tourist survey indicated high levels of visitor experience and education. A heightened perception of crowding with increasing group numbers was reported, however tourist perception of disturbance to manta rays during interactions was low. Analysis of general habitat usage identified Bateman Bay as a critical habitat for feeding, cleaning and courtship behaviour, and found that tourist interactions take place in these same critical habitat areas. Sighting demographics indicated that the majority of interactions were with resident female manta rays, further emphasising the need for management; these females are not only subjected to interactions throughout the entire year, they also are more dependent on critical habitat areas, and may be important breeding individuals within the population. The tour operators observed in this study voluntarily adhered to the Code of Conduct for Manta Ray Interactions designed to minimise disturbance to the manta ray population. These results therefore represent the level of short-term responses induced by compliant operators. The efficiency of the code of conduct in minimising disturbance to manta rays remains unknown, since the long-term implications of short-term behavioural changes are yet to be determined, as are the compliance levels of operators not observed in this study. Given this uncertainty, it is recommended that all operators be required to adopt a mandatory code of conduct to ensure consistency across the industry that can be monitored accordingly. On-going assessment of behavioural responses along with operator compliance, and monitoring of the manta ray population is also recommended.