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Reef accessibility impairs the protection of sharks

Tom Letessier, Jessica Meeuwig | Oct 18, 2017

Tom Letessier, Jessica Meeuwig

Oct 18, 2017

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Remote reefs are the last sanctuaries for reef sharks. Photo: National Geographic Pristine Seas.

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CITATION

Juhel JB, Vigliola L, Mouillot D, Kulbicki M, Letessier TBL, Meeuwig JJ, Wantiez L. 2017. Reef accessibility impairs the protection of sharks. Journal of Applied Ecology. DOI: 10.1111/1365-2664.13007.

ABSTRACT

Reef sharks are declining world-wide under ever-increasing fishing pressure, with potential consequences on ecosystem functioning. Marine protected areas (MPAs) are currently one of the management tools used to counteract the pervasive impacts of fishing. However, MPAs in which reef sharks are abundant tend to be located in remote and underexploited areas, preventing a fair assessment of management effectiveness beyond remoteness from human activities. Here, we determine the conditions under which MPAs can effectively protect sharks along a wide gradient of reef accessibility, from the vicinity of a regional capital towards remote areas, using 385 records from baited remote underwater video systems and 2,790 underwater visual censuses performed in areas open to fishing and inside 15 MPAs across New Caledonia (South-Western Pacific).

We show that even one of the world’s oldest (43 years), largest (172 km2) and most restrictive (no-entry) MPA (Merlet reserve) on coral reefs has between 17.3% and 45.3% fewer shark species and between 37.2% and 79.8% fewer shark abundance than remote areas in a context where sharks are not historically exploited. On coral reefs situated at less than 1 hr of travel time from humans, shark populations are so low in abundance (less than 0.05 individuals per 1,000 m2) that their functional roles are severely limited. Synthesis and applications. Remote areas are the last sanctuaries for reef sharks, providing a new baseline from which to evaluate human impacts on the species. However, there is no equivalent close to human activities even in large, old and strongly restrictive marine protected areas. As such sharks deserve strong protection efforts. The large, no-entry marine protected areas, close to humans, offer limited benefits for reef shark populations, but provide more realistic conservation targets for managers of human-dominated reefs. The exclusion of human activities on a sufficiently large area is key to protect reef shark populations. However, this strategy remains difficult to apply in many countries critically depending on reef resources for food security or livelihood.

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GOING THE DISTANCE TO SURVIVE

Species richness and abundance of sharks as a function of reef accessibility. Each dot represents one census. Figure: Juhel et al. 2017.

FUNDING & ACKNOWLEDGEMENTS

We thank Gérard MouTham and Joseph Baly for processing a large quantity of stereo video footage. We are grateful to the crews of R/V Amborella and R/V Alis, the two vessels we used in the study. This study is part of the PRISTINE project funded by the TOTAL Foundation. We also thank José Fabricio Vargas for some of the scientific drawings of sharks used in the supplementary material, and Dr. Justin Rizzari and Dr. Rowan Trebilco for valuable comments on the manuscript.