Turtle density around Mussau Island, Papua New Guinea: with notes on the practicality of in-water distance sampling

Abstract

Despite sea turtles in Papua New Guinea being culturally important and heavily harvested, no in-country density estimates have been previously established. We provide the first estimates of sea turtle density in Papua New Guinea from two locations around Mussau Island where turtle consumption is banned due to religious beliefs. We obtained density estimates using a low-cost, in-water distance sampling method. Our monitoring shows that the island has a high density of sea turtles (almost exclusively Chelonia mydas). At Lolieng, a site with a steep reef drop off, we recorded a mean of 7.4 turtles ha−1 (s.d. = 2.6) at the reef crest during low tide (across all sampling occasions), which is comparable to high density sites globally. By comparison, we recorded a much lower estimate of 1.1 turtles ha−1 (s.d. = 0.4) at Nae, a site with an extensive, low profile reef system. Additionally, our modelling shows that tidal cycle is an essential covariate for assessing sea turtle density for in-water distance sampling. We advocate that Papua New Guinea needs to invest in long-term monitoring at a national scale to track the sustainability of this important cultural resource, and that in-water distance sampling is a low cost monitoring method that potentially could be used for this purpose albeit subject to certain caveats.