Feral pig predation threatens the Indigenous harvest and local persistence of snake-necked turtles in northern Australia

Northern snake-necked turtles (Chelodina rugosa) traditionally provided an important seasonal source of protein for indigenous communities in Arnhem Land, northern Australia. Harvest techniques today differ little from those used historically, harvesting being applied in the late dry season when ephemeral waters have drawn down and turtles are aestivating. Radio-telemetry was used to quantify survival rates of C. rugosa at a traditional turtle harvest site and relate them to harvest, predation by feral pigs (Sus scrofa) and environmental factors. Although turtle survival was positively correlated with body size, the survival of turtles of all sizes and stages of maturity was compromised by pig predation. Seasonal variation in the onset, duration and severity of rainfall and associated influences on periodic drying, are important for C. rugosa survival because such variation influences the timing and intensity of both Aboriginal harvest and pig predation. Contemporary harvest rates of C. rugosa in Arnhem Land by Aboriginal people are very low because pig predation depletes available stocks immediately before Aboriginal harvesting. Aboriginal harvest rates are regulated also by the frequency and timing of ceremonies and other cultural activities that interfere with harvests. Before the arrival of pigs, such relaxation of harvest pressure in years when harvest would otherwise be possible would have contributed to the local abundance and persistence of C. rugosa. In contrast, pig predation is unrelenting, and years of high turtle survival are now restricted only to years of high wet season rainfall.