Risk and resilience: high stakes for sharks making transjurisdictional movements to use a conservation area.
AuthorsOliver, Simon P.
AffiliationUniversity of Chester; Rutgers University Marine Field Station; Scotish National Heritage; The Thresher Shark Research and Conservation Project; Divelink Cebu; Evolution Dive Resort; Scubazoo
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AbstractOceanic sharks are vulnerable to overexploitation due to their life-history strategies, and declines in their populations are well documented. While it is clear that pelagic sharks are often subjected to uncontrolled fishing for their meat and valuable fins, a lack of empirical knowledge, and transboundary jurisdictional issues have stalled many initiatives to protect them in the wild. Alopiids, including pelagic thresher sharks, are important to Asian fisheries, but the extent to which they are exploited in the Philippines is unknown. We fitted 14 pelagic thresher sharks with acoustic tags, and monitored their fine scale lateral movements near a seamount in the Central Visayas where their regular occurrence is prized as a tourism enterprise. Pelagic thresher sharks used a specific corridor to move away from the seamount after early morning visits to cleaner wrasse. Long range dispersals occurred at a mean rate of 3.79 ± 1.43 km h-1 and were attributed to foraging behavior. Daily foraging expeditions led pelagic thresher sharks to potentially venture across the jurisdictional waters of five provincial territories even when they regularly returned to the seamount. Thresher sharks preferred specific locations on the seamount where they interact with cleaner fish. While the seamount offers cleaner associated services and refuge provision for these rare and elusive sharks, disconnects between habitual predator and prey localizations are likely to increase their vulnerability to pressure from large scale fisheries that operate in the area.
CitationOliver, S. P., Grothues, T. M., Williams, A. L., Cerna, V., Silvosa, M., Cases, G., Reed, M. & Christopher, S. (2019). Risk and resilience: high stakes for sharks making transjurisdictional movements to use a conservation area. Biological Conservation, 230. 58-66. doi: 10.1016/j.biocon.2018.11.013
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