How Marine Protected Areas are Safeguarding Our Ocean’s Vulnerable Top Predators

By GLORES Science Intern, Abbie Dosell

Sharks are an essential part of marine ecosystems, asserting top-down control that maintains ecosystem balance. However, these beloved predators are consistently threatened by fisheries bycatch, pollution, habitat loss and shark finning. Shark finning alone is estimated to be responsible for the deaths of 73 million sharks annually. Sharks and rays are commercially valuable for their fins, meat, liver oil, gill rakers and leather, and they are an important source of food security [1]. The Food and Agriculture Organization conservatively estimates the value of shark fin imports in 2011 was USD 438.6 million and that of shark meat imports was USD 379.8 million [2].

Given these threats, it is essential that marine conservation strategies consider the protection of sharks to prevent further declines, allow populations to recover from overexploitation and maintain healthy ecosystems. Marine protected areas (MPAs) are protecting many shark populations around the world along with the ecosystems in which they play such important roles.

There is strong evidence of site fidelity in some reef shark species, particularly among juveniles [4]. This fidelity enables well-designed MPAs to safeguard these species’ early life history by protecting their home ranges. In addition to juvenile site fidelity, several tropical carcharhinid species have relatively small home ranges throughout their life cycle. Well-protected marine reserves have significant positive effect on such shark species, likely as a result of enhanced prey availability and reduced mortality from fishing [5].

Sharks are abundant in Misool Private Marine Reserve, a Global Ocean Refuge in the Raja Ampat region of Indonesia. Photo credit: Shawn Heinrichs

Many sharks, though, are highly mobile creatures; for example, whale sharks have been found to cover distances of over 20,000 km [3], and as a result they rarely remain within the boundaries of a single MPA. For these less site-attached shark species, MPAs can play a vital role in the protection of vulnerable habitats where sharks aggregate, such as nurseries and mating grounds [6,7,8]. Sharks are often found in higher abundances and among more species around pelagic biodiversity hotspots such as seamounts and in the waters surrounding remote islands [9]. For example, hammerhead sharks tagged in the Galápagos Islands preferred these types of remote hotspots and often migrated among the hotspots, but rarely remained outside of the hotspots; similar patterns were observed in other pelagic species [10]. And scientists are still unravelling the mysterious concentration of white sharks at an isolated location in the Pacific, dubbed the “White Shark Café” [11]. Understanding and identifying the spatial distributions of sharks and using this to inform MPA placement and design can lead to MPAs that protect essential habitats for highly-mobile, pelagic shark species.

However, despite the evident successes of MPAs in safeguarding sharks [12], there is room for improvement in the design, governance [13] and enforcement [14] of MPAs to better protect sharks. Conservation efforts need to focus on socioeconomic aspects of MPAs in order to improve protections for the top predators that play such a key role in many coastal community economies. MPA success depends on compliance which is closely tied to local buy-in for many coastal MPAs. A focus on local livelihood benefits will be essential for these MPAs to enhance protection for sharks [15].

References

[1] Davidson et al. (2015) Why have global shark and ray landings declined: improved management or overfishing? Fish and Fisheries 17(2):438-458.

[2] FAO (2015) State of the global market for shark products.

[3] Guzman et al. (2018) Longest recorded trans-pacific migration of a whale shark (Rhincodon typus). Marine Biodiversity Records 11:8.

[4] Garla et al. (2006) Movement patterns of young Caribbean reef sharks, Carcharhinus perezi at Fernando de Noronha Archipelago, Brazil: the potential of marine protected areas for conservation of a nursery ground. Marine Biology 149:189-199.

[5] Bond et al. (2012) Reef sharks exhibit site fidelity and higher relative abundance in marine reserves of the Mesoamerican Barrier Reef. PLoS ONE 7:3.

[6] Bonfil, R. (1999) Marine protected areas as a shark fisheries management tool. Proceedings of the 5th Indo-Pacific Fish Conference, 1997.

[7] Stevens, J. (2002) The role of protected areas in elasmobranch fisheries management and conservation. Elasmobranch biodiversity, conservation and management. Proceedings of the international seminar and workshop, Sabah, Malaysia 1997.

[8] Barker, MJ and Schluessel, V. (2005) Managing global shark fisheries: suggestions for prioritising management strategies. Marine and Freshwater Ecosystems 15(4): 325-347.

[9] Hearn et al. (2010) Hotspots within hotspots? Hammerhead shark movements around Wolf Island, Galapagos Marine Reserve. Mar. Biol. 157:1899-1915.

[10] Hearn et al. (2010) Hotspots within hotspots? Hammerhead shark movements around Wolf Island, Galapagos Marine Reserve. Mar. Biol. 157:1899-1915.

[11] Jorgensen et al. (2010) Philopatry and migration of Pacific white sharks. Proc. R. Sci. B 277:679-688.

[12] White et al. (2017) Asessing the effectiveness of a large marine protected area for reef shark conservation. Biological Conservation 207:64-71.

[13] Mackeracher et al. (2018) Sharks, rays and marine protected areas: A critical evaluation of current perspectives. Fish and Fisheries 2018:1-13.

[14] White et al. (2017) Asessing the effectiveness of a large marine protected area for reef shark conservation. Biological Conservation 207:64-71.

[15] Mackeracher et al. (2018) Sharks, rays and marine protected areas: A critical evaluation of current perspectives. Fish and Fisheries 2018:1-13.