Indigenous harvest, exotic pig predation and local persistence of a long-lived vertebrate: managing a tropical freshwater turtle for sustainability and conservation.
Abstract
Until recently, the northern snake-necked turtle (Chelodina rugosa Ogilby, 1890) provided a seasonal source of protein for indigenous communities in tropical northern Australia. Today, feral pigs (Sus scrofa Linnaeus, 1758) exert a heavy predation pressure on C. rugosa, compromising subsistence harvest rates and threatening local persistence. We investigated the influence of pig predation and harvest (subsistence and commercial) on C. rugosa persistence at discrete water holes using a stage-based matrix population model. Vital rates varied with wet season rainfall, pig predation and harvest. In addition, hatchling survival was density-dependent. We show that field-based estimates of pig-related turtle mortality exceed levels that can be offset by increased hatchling survival, leading to predictions of rapid population decline and certain elimination of affected populations within 50 years. Conversely, in the absence of pigs, compensatory increases in hatchling survival were sufficient to allow an annual harvest of up to 20% of subadult and adult C. rugosa without causing extirpation or substantial population suppression. Synthesis and applications. This demographic modelling shows that periodic local culling of pigs, fencing of wetlands to exclude predators, and hatchling supplementation to offset losses from predation are all viable management strategies for ensuring ongoing turtle harvests. Such demonstrations of the potential resilience of long-lived vertebrates under a properly managed harvest regime is important to convince natural resource agencies that conservation management for long-term viability need not exclude some degree of consumptive use. These findings are broadly relevant to applied ecology, providing important implications for the management of wildlife species subject to competing ecological pressures, such as subsistence and commercial harvesting and predation by invasive species.