Ecological consequences of toxin use for mammalian pest control in New Zealand—An overview

Toxins, especially sodium monofluoroacetate (1080) and brodifacoum, are widely used throughout New Zealand for control of introduced mammals that are considered pests. This level of toxin use (not necessarily with these toxins) is unlikely to decline for at least 5-10 years. Ecological consequences derive both from mammal population reduction or eradication, and from using toxins as the control method. Scientists have not examined the net ecological outcomes of these consequences at the community level due to their daunting complexity, although managers usually manipulate whole communities and key conservation legislation demands that they do so. A food web could be a useful conceptual framework to generate hypotheses about toxin movement through communities, and to explore net outcomes of pest control at the community level. It could also sharpen objectives for ecosystem restoration on the New Zealand mainland, and help to find common ground between different participants in ecosystem management. We interpret present evidence to suggest that the ecological costs of using toxins are much less than the damage costs if they are not used, due to the magnitude of known impacts of introduced pest mammals. This suggestion deserves exploration; it may not be true when persistent toxins such as brodifacoum are used rePeatedly. Research on toxin use should continue on its present broad front, but we suggest that priorities are to measure net ecological outcomes at the community level, to reduce toxin use, and to improve pest control strategies and techniques in the maintenance phase of control operations. Finally, we suggest that an annual ecosystem management conference in New Zealand, which explicitly brings together managers, policymakers, landowners, and scientists from the many disciplines now relevant to the complex field of pest mammal control, would enhance progress and co-operation.