Sick of attention: The effect of a stress-related disease on juvenile green sea turtle behaviour in the face of intense and prolonged tourism

Anthropogenic activities are increasingly linked to emerging diseases that cause mortality across many taxa. Human interference through ecotourism, in particular, can increase the stress levels of wild populations and promote the spread of disease. In Akumal Bay, Mexico, green sea turtles (Chelonia mydas) are increasingly infected with fibropapillomatosis (FP), an infectious disease associated with stress-induced immunosuppression linked to high human density, which is particularly high in this area because of intense and prolonged ecotourism. To examine if FP might be associated with behavioural indicators of stress and varying levels of tourist pressure, we observed the behaviour of turtles and the number of tourists through 20-minute focal sampling periods from May to August 2017. We related disease presence and tourist pressure to several aspects of turtle behaviour, specifically feeding, resting, vertical movements (i.e., surfacing and diving), and evasive responses. Turtles that had FP engaged in fewer feeding periods, vertical movements, and evasive responses. Additionally, with increasing tourist pressure, all turtles spent less time engaging in vertical movements and had more evasive responses. Our results suggest that the presence of FP affects green sea turtle behavior, potentially increasing their exposure to tourists. Sick and healthy turtles appear to react differently to tourists, suggesting that FP weakens behavioural responses to tourist pressure. Future management strategies should consider regulating tourist pressure on turtles to reduce the incidence and progression of FP.