Recent expansion of marine protected areas matches with home range of grey reef sharks

Lucas Bonnin,William D Robbins,Laurent Vigliola,Jeremy J Kiszka,David Mouillot,Germain Boussarie,Laurent Dagorn

doi:10.1038/s41598-021-93426-y

Abstract

Dramatic declines in reef shark populations have been documented worldwide in response to human activities. Marine Protected Areas (MPAs) offer a useful mechanism to protect these species and their roles in coral reef ecosystems. The effectiveness of MPAs notably relies on compliance together with sufficient size to encompass animal home range. Here, we measured home range of 147 grey reef sharks, Carcharhinus amblyrhynchos, using acoustic telemetry in New Caledonia. The distribution of home range was then compared to local MPA sizes. We report a home range of 12 km2 of reef for the species with strong differences between adult males (21 km2), adult females (4.4 km2) and juveniles (6.2 km2 for males, 2.7 km2 for females). Whereas local historic MPA size seemed adequate to protect reef shark home range in general, these were clearly too small when considering adult males only, which is consistent with the reported failure of MPAs to protect sharks in New Caledonia. Fortunately, the recent implementation of several orders of magnitude larger MPAs in New Caledonia and abroad show that recent Indo-Pacific MPAs are now sufficiently large to protect the home ranges of this species, including males, across its geographical range. However, protection efforts are concentrated in a few regions and cannot provide adequate protection at a global scale.

Highlights

Dramatic declines in reef shark populations have been documented worldwide in response to human activities
Twenty-five Marine Protected Areas (MPAs) are currently established in New Caledonian waters (Table S1), with restriction levels ranging from the prohibition of all extractive activities such as fishing to the prohibition of all human activities including the entrance of ships
The lack of efficiency of MPAs implemented in New Caledonia before 2010 to protect reef shark populations[9,19] may be attributed to a large suite of factors, such as illegal fishing[51,52] and human proximityinduced fitness alterations[19]

Summary

Introduction

Dramatic declines in reef shark populations have been documented worldwide in response to human activities. Whereas local historic MPA size seemed adequate to protect reef shark home range in general, these were clearly too small when considering adult males only, which is consistent with the reported failure of MPAs to protect sharks in New Caledonia. Regulations within their boundaries, MPAs should be sufficiently large to limit the spread of individuals exiting to surrounding areas open to fishing This can be an issue for mobile species such as sharks. Recognizing that the effectiveness of an MPA to protect mobile species partly relies on its ability to encompass the home range of individuals, i.e. the area where animals spend most of their time[26,27,28,29,30,31], a critical step in assessing the effectiveness of current MPAs for mobile reef shark species should consist in comparing individuals’ home ranges with the size of protected areas

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Conclusion