Regional variation in anthropogenic threats to Indian Ocean whale sharks
Conservation and management of mobile marine species requires an understanding of how movement behaviour and space-use varies among individuals and populations, and how intraspecific differences influence exposure to anthropogenic threats. Because of their long-distance movements, broad distribution and long lifespan, whale sharks (Rhincodon typus) can encounter multiple, cumulative threats. However, we lack knowledge on how sharks at different aggregations use their habitats, and how geographic variation in anthropogenic threats influences their vulnerability to population decline. Using movement data from 111 deployments of satellite-linked tags, we examined how whale sharks at five aggregations in the Indian Ocean varied in their exposure to six anthropogenic impacts known to threaten this endangered species. Tagged sharks were detected in territorial waters of 24 countries, and international waters, with individuals travelling up to 11,401 km. Despite long-distance movements, tagged sharks from each aggregation occupied mutually exclusive areas of the Indian Ocean, where they encountered different levels of anthropogenic impacts. Sharks in the Arabian Gulf had the greatest proximity to oil and gas platforms, and encountered the warmest sea surface temperatures and highest levels of shipping, pollution and ocean acidification, while those from the Maldives and Mozambique aggregations had the highest exposure to fishing and human population impacts respectively. Our findings highlight the need for aggregation-specific conservation efforts to mitigate regional threats to whale sharks. Multinational coordination is essential for implementing these efforts beyond national jurisdictions and tackling issues of global conservation concern, including the consequences of climate change and an expanding human population.