Assessing the effectiveness of a large marine protected area for reef shark conservation

Abstract

Large marine protected areas (MPAs) have recently been established throughout the world at an unprecedented pace, yet the value of these reserves for mobile species conservation remains unclear. Reef shark populations continue to decline even within some of the largest MPAs, fueling unresolved debates over the ability of protected areas to aid mobile species that transit beyond MPA boundaries. We assessed the capacity of a large MPA to conserve grey reef sharks - a Near Threatened species with a widespread distribution and poorly understood offshore movement patterns - using a combination of conventional tags, satellite tags, and an emerging vessel tracking technology. We found that the 54,000 km2 U.S. Palmyra Atoll National Wildlife Refuge in the central Pacific Ocean provides substantial protection for grey reef sharks, as two-thirds of satellite-tracked sharks remained within MPA boundaries for the entire study duration. Additionally, our analysis of > 0.5 million satellite detections of commercial fishing vessels identified virtually no fishing effort within the refuge and significant effort beyond the MPA perimeter, suggesting that large MPAs can effectively benefit reef sharks and other mobile species if properly enforced. However, our results also highlight limitations of place-based conservation as some of these reef-associated sharks moved surprising distances into pelagic waters (up to 926 km from Palmyra Atoll, 810 km beyond MPA boundaries). Small-scale fishermen operating beyond MPA boundaries (up to 366 km from Palmyra) captured 2% of sharks that were initially tagged at Palmyra, indicating that large MPAs provide substantial, though incomplete, protection for reef sharks

Evidence for rapid recovery of shark populations within a coral reef marine protected area

“…Our study reef lies at the edge of the shelf with the nearest coral habitat (Cartier Reef) only ca. 50km to the southeast, a distance easily negotiated by adult C. amblyrhynchos (Heupel et al 2010;White et al 2017). However, Cartier Reef is very small in size (4.5 km by 2.3 km) relative to Ashmore Reef.…”

“…This uncertainty is largely due to the ubiquitous nature of fishing in coral reef ecosystems worldwide (Newton et al 2007). These issues are pertinent to the establishment of management strategies such as marine protected areas (MPAs) (Bond et al 2012;White et al 2017) and shark sanctuaries (Ward-Paige et al 2012) that have been promoted as a means of ensuring the conservation and recovery of shark populations. They add to other unanswered questions about this approach to management and its efficacy (Davidson 2012), such as the optimal size and placement of MPAs, whether they are useful for all components of a shark fauna including wide-ranging apex predators (Ward-Paige et al 2012) and mesopredators (White et al 2017), and the level of enforcement that is required to have desired effects for shark populations (Ward-Paige 2017).…”

“…These issues are pertinent to the establishment of management strategies such as marine protected areas (MPAs) (Bond et al 2012;White et al 2017) and shark sanctuaries (Ward-Paige et al 2012) that have been promoted as a means of ensuring the conservation and recovery of shark populations. They add to other unanswered questions about this approach to management and its efficacy (Davidson 2012), such as the optimal size and placement of MPAs, whether they are useful for all components of a shark fauna including wide-ranging apex predators (Ward-Paige et al 2012) and mesopredators (White et al 2017), and the level of enforcement that is required to have desired effects for shark populations (Ward-Paige 2017). It is generally agreed that strict enforcement is paramount to the success of an MPA Dulvy 2006;Edgar et al 2014;Gill et al 2017), although even well-managed parks such as the Great Barrier Reef Marine Park have seen declines in common species of reef sharks due to illegal fishing in no-take zones ).…”

Accounting for detection gaps when evaluating reef fish habitat use in an acoustic array

“…Efficient spatial management strategies require protected areas to contain critical habitats and to have boundaries aligned with natural barriers to movement, reducing the spillover of spawning stock biomass into fishable areas. Sufficiently large MPAs that contain critical habitats can provide substantial protection, even to highly mobile predators (White et al 2017). To maximize fisheries benefits, no-take MPAs should contain important D r a f t habitats that allow organisms to maximize growth and reduce risk of predation (MacArthur & Pianka 1966).…”

Occurrence of the rare and Endangered Ornate Eagle Ray, Aetomylaeus vespertilio (Bleeker, 1852) (Chondrichthyes, Myliobatidae), at a remote marine protected area in the Philippines

“…For example, the White-spotted Eagle Ray, Aetobatus narinari (Euphrasén, 1790), displays strong site affinity and localized movements (Ajemian andPowers 2014, Flowers et al 2017), and therefore, spatially-focused management would protect this species during at least part of its life history. However, this would likely be incomplete, as it has been shown in other elasmobranch species, like the reef-associated Grey Reef Shark, Carcharhinus amblyrhynchos (Bleeker, 1856) (White et al 2017). A multidisciplinary approach to chondrichthyan conservation might be optimal, by means of having spatial, temporal, size, and gear restrictions in artisanal and commercial fisheries (Dulvy 2013), depending on the level of engagement and implementation possible.…”