Sins of omission and sins of commission: St Thomas Aquinas and the devil

As the largest surviving marsupial carnivore, the Tasmanian devil is an iconic species. A disfiguring and invariably fatal facial cancer, first reported in 1996, has now spread across most of the range of the devil, leading to population declines of up to 90% and a prognosis of likely extinction in 15-20 years. Transmission experiments have confirmed that the cancer is infectious and genetic evidence shows that it is a transmissible cell line. Potential management strategies are limited, but include establishing insurance populations, disease suppression by removal of infected individuals, selection for resistance and developing a vaccine. None of these strategies is guaranteed to be successful. Some, such as establishing free-ranging populations on offshore islands that currently have no devil population, might possibly impact on other threatened species. We evaluate the range of management options and argue that conservation biologists sometimes prefer “sins of omission”, failing to take action, with attendant risks, over “sins of commission”, taking actions that might backfire.