High mortality and small population size prevent population recovery of a reintroduced mesopredator

Northern Australia's native mammal fauna has undergone a severe decline in recent decades. Putative factors include altered fire regimes, cat predation, poisoning by cane toads and disease. Populations of northern quolls, Dasyurus hallucatus severely declined following cane toad invasion and have not recovered. We monitored a population of northern quolls in Kakadu National Park that was supplemented with ‘toad-smart’ individuals, to determine whether cane toad poisoning or predation was preventing population recovery. The population increased after supplementation, but crashed in March 2012, coincident with a high level of trap disturbance by canids. Canid predation was the major source of mortality for radio-tagged quolls. We used population viability analyses (PVA) to explore how changes in mortality influenced the likelihood of extinction. With no management, the quoll population has a 48% chance of extinction over the next 20 years. Sensitivity analyses highlighted small population size and high mortality as the main reasons for the population failing to recover. We then explored whether population supplementation or reducing mortality could increase the likelihood of persistence. One year of supplementation increased the probability of population survival over 20 years from 51.6% to 81.7%. Continuing supplementation for 3 or 5 years increased the probability of population survival to 96.5% and 98.1% respectively. Similarly, a 2.5% reduction in the rate of mortality for juveniles and adult females increased the probability of population persistence over 20 years to 83.6%. Further reductions in mortality of 5% and 10% increased the probability of survival to 92.2% and 99.4% respectively. The results of the PVA suggest that small interventions could have a significant positive effect on population survival. We hypothesize that predation from food-subsidized canids is preventing the recovery of quoll populations. Future management actions to reduce mortality, via improved fire management, or through population supplementation, are necessary to ensure the persistence of the northern quoll.