Tubbataha Reefs Natural Park: the first comprehensive elasmobranch assessment reveals global hotspot for reef sharks

Abstract

Elasmobranchs are experiencing population declines worldwide because of anthropogenic stressors. Marine protected areas (MPAs) have been shown to benefit mesopredatory species of shark. The Tubbataha Reefs Natural Park (TRNP) is a United Nations Educational, Scientific and Cultural Organization World Heritage Site and the largest no-take MPA in the Philippines, yet information on the current status of elasmobranchs in the park is limited. Here, we investigate the abundance and biodiversity of elasmobranchs in TRNP using underwater visual census (UVC) and baited remote underwater video (BRUV) surveys. Twenty UVC were conducted in May 2015 (n = 10) and June 2016 (n = 10), documenting eight species of elasmobranchs with an average density of 7.18 sharks ha-1 for both years. A total of 113 successful BRUV surveys were conducted in TRNP between March–June 2015 (n = 47) and April–June 2016 (n = 66). The BRUV surveys recorded 14 species with an average catch per unit effort of 2.09 elasmobranchs per hour for both years. Both survey methods report some of the highest densities of the grey reef shark Carcharhinus amblyrhynchos and the whitetip reef shark Triaenodon obesus documented worldwide. This study underlines the importance of large, well-managed MPAs such as TRNP for the conservation of reef-associated elasmobranchs. Keywords: Baited remote underwater video, Elasmobranch conservation, Marine protected area, Reef sharks, Southeast Asia