Global scale tracking of movements, space use and behaviour of marine megafauna to assess impacts of anthropogenic threats for conservation

Abstract

Many marine megafauna are experiencing increased risk of population declines from exposure to anthropogenic threats including climate change, ship collisions and overfishing. As they frequently cross multiple jurisdictional boundaries, conservation of these ocean giants remains challenging, not least because robust data on their movement, space use and behaviour across multiple scales are either not available or have not been collected over most of their population ranges. With predicted declines in megafauna populations likely to result in substantial ecosystem-service loss, developing advanced technologies and analyses to determine where, when and how much key habitats overlap with anthropic threats is now a critical step in conserving wider ecosystem functioning. This thesis examines the movements, space use and habitat preferences of the globally endangered whale shark, Rhincodon typus, to quantify the potential impacts of anthropogenic threats at global, regional, and local scales. Exploring the direct and indirect impacts of human activity on this species is needed to address the ongoing population decline documented for whale sharks. At the global scale, over 340 individual whale shark movements resulting from satellite tracking were used to quantify the risk of collision (potentially leading to direct mortality) between this species and global shipping fleets. High spatial and temporal overlap between sharks and ships was found, with potential collisions recorded in the tracking dataset indicating lethal ship strikes were possible for approximately 24% of a subset of tracked sharks. Overall, collision risk was determined to be greater than previously realised and may be largely responsible for observed population declines. However, whale sharks were not tracked in many areas of the ocean. To address spatial gaps in movement data, species distribution models were developed to determine areas of habitat suitability in remote locations as well as those used by the individuals tracked. Models performed well in external validation tests with regional variation in habitat suitability linked to changes in oceanographic conditions. At the local scale, important habitats shifted within Exclusive Economic Zones (EEZs) of many countries, identifying opportunities for targeted conservation and international cooperation in the present day. At broader regional scales, substantial habitat shifts were apparent when models were used to project whale shark space use into future environments; these include poleward shifts in both northern and southern hemispheres of up to 2,000 km by 2100. Changes in habitat were linked to shifting environmental conditions under climate change scenarios. In the future, collision risk for sharks with vessels was estimated to increase beyond current levels as habitats were projected to shift into busier shipping areas. With no sign of declines in human activity in the global ocean on the horizon, this research demonstrates the need for adaptive management that mitigates direct threats to highly-mobile marine megafauna such as whale sharks, but that also develops such mitigations with reference to climate change that will alter the location and extent of wildlife-human interactions in the future.

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