Modelling the policy and economic context for detection- based monitoring tools: the costs and benefits of detecting last survivors and first re-colonisers

Establishing and maintaining the success of pest or weed eradication programmes requires interpretation of failures to detect survivors and first re-colonisers. Recent developments provide statistical frameworks that allow sequences of such failures to be interpreted in a probabilistic context. For example, application of these methods allow managers of eradication programmes to decide a priori an acceptable risk of programme failure, and to use this decision to design monitoring regimes that deliver this level of certainty, given the detection characteristics of the search techniques at their disposal. Similar methods could be use to design monitoring regimes to detect an incursion by a previously eradicated species (i.e. an eradication breakdown), which have an acceptable risk of failure. However, the availability of these methods begs questions about how “acceptable” risks of eradication failure or breakdown should be specified, and the consequent effort that should be expended to locate last survivors and first re- colonisers. We use a risk-based bioeconomic framework to model and analyse these decisions. The analysis demonstrates critical trade-offs between the cost and efficacy of the detection techniques available, the “value” of the eradication programme, and the perceived risk that a breakdown can occur. While our focus is on island pest eradication, we suggest how the bioeconomic framework used could be usefully applied to the detection of rare, at risk species, and the management of sporadically frequent diseases.