Résumé
1. Reef sharks are declining worldwide under ever increasing fishing
pressure with potential consequences on ecosystem functioning. Marine
protected areas (MPAs) are currently one of the management tools 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. 2. 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
(BRUVS) and 2790 Underwater Visual Censuses (UVC) performed in areas open
to fishing and inside 15 MPAs across New Caledonia (south-western
Pacific). 3. We show that even one of the world’s oldest (43 years), large
(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. 4. On coral reefs situated at less
than 1 hour of travel time from humans, shark populations are so low in
abundance (less than 0.05 individuals per 1000 m²) that their functional
roles is severely limited. 5. Synthesis and applications. Remote areas are
the last sanctuaries for reef sharks and provide a new baseline to
evaluate human impacts with no equivalent close to human activities even
in large, old and strongly restrictive MPAs. As such they deserve strong
protection efforts. The large and no-entry MPAs 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.14-Aug-2017