Marine turtle nest depredation by feral pigs (Sus scrofa) on the Western Cape York Peninsula, Australia: implications for management

Context The west coast of the Cape York Peninsula (CYP) is a major nesting ground for three species of threatened marine turtle, namely, the flatback (Natator depressus), olive ridley (Lepidochelys olivacea) and hawksbill (Eretemochelys imbricata). Marine turtle nests in this area experience high rates of depredation and unpublished data from numerous studies have suggested that feral pigs are responsible for most nest losses. Aims The aim of the present study was to identify the relative magnitude of nest mortality associated with physical processes versus depredation and to distinguishing between two possible pig depredation scenarios. Methods We documented laying and mortality patterns on Pennefarther Beach (CYP) over a 49-day period in 2007. We partitioned mortality into components attributable to beach erosion, inundation and depredation and also assessed the relative magnitude of depredation associated with different nest predators. We used these data to test whether the temporal and spatial pattern of pig depredation was random with respect to patterns of nest availability. Key results The overall level of nest mortality was 40.2%. Depredation was responsible for 93% of nest losses. Pig predation was high, accounting for 89.6% of all mortality. Depredation occurred equally across nests of all three turtle species. Although nests were laid uniformly in both time and space, pig depredation was significantly clustered. Conclusions Depredation by feral pigs was the principal cause of turtle nest mortality in the present study. The pattern of nest destruction was consistent with the occurrence of pig depredation by single individuals in discrete feeding areas. Implications Current feral pig management involves aerial shooting. This is effective at removing large numbers of animals over large areas. However, aerial shooting is also expensive. Our results suggest that targeted monitoring and eradication of locally active individuals depredating nests may better manage pig impacts, specifically those on turtle nests.