First Report on the Density and Size Frequency Distribution of the Napoleon Wrasse, Cheilinus undulatus in the Tubbataha Reefs Natural Park, Philippines

Abstract

The Napoleon wrasse – Cheilinus undulatus, locally known as “mameng” – was assessed as “endangered” in 2004 under the International Union for Conservation of Nature (IUCN) Red List assessment and is also listed under the Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Although there are numerous reports of Napoleon wrasse sightings by tourists and researchers in the two atolls within the Tubbataha Reefs Natural Park (TRNP), its density and size-frequency distribution have not been formally documented. A thorough survey was conducted in TRNP in May 2017 employing the fish visual census (FVC) technique but with a much broader swath width. A total reef area of 103 hectares not frequently visited by tourists was surveyed in the North and South Atolls, where a total of 641 individuals was recorded with an average density of 6.83 individuals/ha. Density comparison between atolls showed a significant difference (Welch’s two-sample t-test (t5.42 = –3.28, p < 0.05). South Atoll has a higher density (8.13 individuals/ha ± 1.11 se) than the North Atoll (4.20 individuals/ha ± 0.46 se). However, by size class, the North Atoll was significantly larger (n = 398; median = 65 cm) than in the South Atoll (n = 243; median = 60 cm) based on Wilcoxon Rank Sum test (W = 55,674, p < 0.05). A comparison of density and size class between the NW and SE coastline in the North Atoll showed no significant difference. Juveniles were also found at a site at the North Atoll. Taken together, these findings suggest that TRNP may serve as a source and a sink at the same time. This implies that TRNP is a key habitat for the Napoleon wrasse in the Sulu Sea and possibly in the adjacent seas through its pelagic larvae.