Movement patterns of silvertip sharks (Carcharhinus albimarginatus) on coral reefs
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Understanding how sharks use coral reefs is essential for assessing risk of exposure to fisheries, habitat loss, and climate change. Despite a wide Indo-Pacific distribution, little is known about the spatial ecology of silvertip sharks (Carcharhinus albimarginatus), compromising the ability to effectively manage their populations. We examined the residency and movements of silvertip sharks in the central Great Barrier Reef (GBR). An array of 56 VR2W acoustic receivers was used to monitor shark movements on 17 semi-isolated reefs. Twenty-seven individuals tagged with acoustic transmitters were monitored from 70 to 731 d. Residency index to the study site ranged from 0.05 to 0.97, with a mean residency (±SD) of 0.57 ± 0.26, but most individuals were detected at or near their tagging reef. Clear seasonal patterns were apparent, with fewer individuals detected between September and February. A large proportion of the tagged population (>71 %) moved regularly between reefs. Silvertip sharks were detected less during daytime and exhibited a strong diel pattern in depth use, which may be a strategy for optimizing energetic budgets and foraging opportunities. This study provides the first detailed examination of the spatial ecology and behavior of silvertip sharks on coral reefs. Silvertip sharks remained resident at coral reef habitats over long periods, but our results also suggest this species may have more complex movement patterns and use larger areas of the GBR than common reef shark species. Our findings highlight the need to further understand the movement ecology of silvertip sharks at different spatial and temporal scales, which is critical for developing effective management approaches.
KeywordsCoral reefs Predator Behavior Acoustic telemetry Sharks Conservation
We thank students and staff from the Centre for Sustainable Tropical Fisheries and Aquaculture for field support, especially J. Matley, E. Lédée, F. de Faria and S. Moore; and the crew from the RV James Kirby. Funding was provided by the National Environmental Research Program (Tropical Ecosystems Hub Project 6.1). MRH was supported by a Future Fellowship (#FT100101004) from the Australian Research Council, and ME was supported by the PADI Foundation, Australian Endeavour and AIMS@JCU Scholarships.
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