The drivers of green turtle, Chelonia mydas, abundance around Mussau Island, Papua New Guinea

Green turtles (Chelonia mydas: Endangered) are found in high numbers around Mussau Island, Papua New Guinea because the island community is made up of Seventh Day Adventists who have a religious prohibition against eating... [ view full abstract ]

Green turtles (Chelonia mydas: Endangered) are found in high numbers around Mussau Island, Papua New Guinea because the island community is made up of Seventh Day Adventists who have a religious prohibition against eating them. Some locals believe turtle herbivory is detrimentally affecting seagrass and seaweed abundance and therefore affecting the viability of both an inshore fishery (Siganidae) and the abundance of edible seaweed. As a consequence some locals were proposing a turtle cull. While we are currently awaiting sufficient data to assess the causative relationship between turtle numbers, seagrass and seaweed we are examining the drivers behind daily changers in turtle abundance. We used distance sampling to determine turtle density and the drivers of daily density changes between reef crest and inshore sites at two locations: Nae and Lolieng. Observers made a total of 381 1 km long transects. To determine turtle density 46 candidate models were considered within a model selection framework. Inshore turtle density was at a maximum during high tide: ~0.5 turtles per ha at Nae and ~5 turtles per ha at Lolieng. Turtle density at the reef crest was at a maximum during low tide: ~1.5 turtles per ha at Nae and ~8 turtles per ha at Lolieng. This represents the first robust estimate of turtle density in Papua New Guinea, and demonstrates the strong effect of tide. Our monitoring also suggests there is circumstantial evidence that turtles may be being prosecuted at Nae.