Residency and Spatial Use by Reef Sharks of an Isolated Seamount and Its Implications for Conservation

A. Peter Klimley,Adam Barnett,Richard Fitzpatrick,Jamie Seymour,Kátya G. Abrantes

doi:10.1371/journal.pone.0036574

Abstract

Although marine protected areas (MPAs) are a common conservation strategy, these areas are often designed with little prior knowledge of the spatial behaviour of the species they are designed to protect. Currently, the Coral Sea area and its seamounts (north-east Australia) are under review to determine if MPAs are warranted. The protection of sharks at these seamounts should be an integral component of conservation plans. Therefore, knowledge on the spatial ecology of sharks at the Coral Sea seamounts is essential for the appropriate implementation of management and conservation plans. Acoustic telemetry was used to determine residency, site fidelity and spatial use of three shark species at Osprey Reef: whitetip reef sharks Triaenodon obesus, grey reef sharks Carcharhinus amblyrhynchos and silvertip sharks Carcharhinus albimarginatus. Most individuals showed year round residency at Osprey Reef, although five of the 49 individuals tagged moved to the neighbouring Shark Reef (∼14 km away) and one grey reef shark completed a round trip of ∼250 km to the Great Barrier Reef. Additionally, individuals of white tip and grey reef sharks showed strong site fidelity to the areas they were tagged, and there was low spatial overlap between groups of sharks tagged at different locations. Spatial use at Osprey Reef by adult sharks is generally restricted to the north-west corner. The high residency and limited spatial use of Osprey Reef suggests that reef sharks would be highly vulnerable to targeted fishing pressure and that MPAs incorporating no-take of sharks would be effective in protecting reef shark populations at Osprey and Shark Reef.

Highlights

Many marine apex predators are under threat from direct exploitation, mortality as bycatch, competition with fisheries and from other anthropogenic impacts such as habitat alteration or degradation [1,2,3,4,5,6,7]
Results suggest that reef sharks at Osprey Reef are permanent residents of the area (Osprey and neighbouring Shark Reef), with very little emigration away from these areas
There are a number of possible reasons why some animals (6 adult and 4 juvenile sharks) were not detected for the entire study: animals could still be present but were in areas of low receiver coverage, they could have emigrated from Osprey Reef, could have died during the study, or the transmitters failed

Summary

Introduction

Many marine apex predators are under threat from direct exploitation, mortality as bycatch, competition with fisheries and from other anthropogenic impacts such as habitat alteration or degradation [1,2,3,4,5,6,7]. As protected areas are unlikely to encompass entire distribution ranges of large predator populations [6,15], the challenge is to implement an area that is large enough to afford sufficient protection to species that are highly mobile, while appeasing human activities [6,16]. Studies on killer whales Orcinus orca and African penguins Spheniscus demersus used behavioural information to prioritise habitats primarily used for the activity in which they are most receptive to anthropogenic disturbance [6,16]. In both cases, the protection of essential foraging grounds was of greater benefit than protecting habitats generically

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Conclusion