Changes in a Feral Pig Population after Poisoning

The changes in a feral pig population associated with 1080 poisoning were examined. There was a 58.1% reduction in population size after poisoning with no age-specific effect. The population size increased over 11.5 months after poisoning at an observed instantaneous rate of increase per year of 0.57. The results are discussed relative to feral pig control. INTRODUCTION Pigs (Sus scrofa) were introduced to New South Wales with white settlement. Subsequently some domestic pigs escaped or were released into the wild, forming feral (wild) pig colonies. By 1950, feral pigs were widespread in north-western New South Wales (Pullar 1950), and by 1977 throughout most of New South Wales (Hone and Waithman 1979). Feral pigs are of agricultural concern in New South Wales because of their current impact on agriculture such as crop damage (Giles 1976, Pullar 1950), lamb predation (Plant et al. 1978), damage to pastures, fences and watering facilities (Pullar 1950), and the dissemination of diseases such as leptospirosis (Keast et al. 1963) and sparganosis (Appleton and Norton 1976). Feral pigs are of considerable concern also for their potential role as a reservoir of infection of several exotic diseases such as foot and mouth disease, swine fever, and African Swine Fever (Murray and Snowdon 1976). The main methods of controlling feral pig damage are poisoning, trapping, shooting, fencing, habitat changes and changes in agricultural management. These would also be the basic methods used to eradicate feral pigs if it was considered necessary in an exotic disease outbreak. The short-term effectiveness of the control methods is usually assessed by the percentage kill, and predictions of its long-term effects are based on knowledge of the remaining population's expected rate of increase. This paper reports a study aimed at measuring the changes in a feral pig population following poisoning with sodium monofluoroacetate (1080). The observed instantaneous rate of increase per year is calculated, and the population examined for an effect of the poisoning on the age structure, sex ratio and social structure which may affect the rate of increase. Observations on bait taken by non-target species are also reported. The study was conducted over one year as field reports suggested that many feral pig populations returned to their pre-poisoning level of abundance in that time.