Reproductive biology of the flatback turtle Natator depressus in Western Australia

Abstract

In contrast to the circumglobal nesting distributions and well-described reproductive biology of most marine turtle species, all known records of flatback turtle Natator depressus nesting have occurred within Australia and are relatively underreported; the species is listed as ‘Data Deficient’ by the International Union for the Conservation of Nature (IUCN). We report important baseline data on the breeding biology of flatback turtles at 3 rookeries in the Pilbara region of Western Australia, an area subject to increasing coastal development due to rapid expansion of the resources sector. Barrow Island and Mundabullangana support substantial reproductive populations; over the 6 season sampling period from 2005/06 to 2010/11, ~4000 and ~3500 turtles were tagged at each location, respectively. Over 2 seasons of monitoring in 2009/10 and 2011/12 at Cemetery Beach, a smaller rookery in Port Hedland, ~350 flatback turtles were tagged. We detected variation in parameters of reproductive biology between island and mainland rookeries. Mean remigration interval at Barrow Island (1.9 yr) was significantly shorter than at mainland Mundabullangana (2.2 yr) and may reflect differences in location and characteristics of remote foraging habitats in turtles returning to mainland versus offshore rookeries. Clutch size was similar (~47 eggs) among rookeries and smaller than mean clutch sizes recorded for all other Australian flatback rookeries (~53 eggs). Hatching success at Barrow Island (83.4%) was within the reported range for the species; however, at Mundabullangana and Cemetery Beach (68.2% and 57.3%, respectively) these values were the lowest published to date for this species and may be attributable to higher temperatures at mainland rookeries.