Bioeconomic modelling in the development of invasive fish policy

Invasive species policy is either explicitly or implicitly underpinned by the question "When should investment in managing the invasive species stop?" Bioeconomic modelling provides a quantitative framework for considering the benefits and costs of alternative levels of investment in invasive species management by linking the level of investment to the costs of intervention (control) and value of benefits derived. Control costs are typically the product of the number of individuals that have to be removed to either eradicate the invasive species or constrain it at some specified density, and the cost of removing each individual. Impact functions take a variety of forms, but in general are systematically related to the density of the managed population. Where impacts can be accounted in monetary terms (e.g., where an invasive species affects income), control costs and benefits can be directly compared and an optimal level of investment (usually that which maximises return on investment) can be identified. However, where impacts do not have a directly accessible monetary value (e.g., where an invasive species affects conservation values), benefits and costs cannot be directly contrasted. Under these circumstances, bioeconomic modelling can be used to identify management strategies that maximise the level of benefit that can be achieved for expenditure of a fixed budget (benefit maximisation), or minimise the cost of achieving a given level of benefit (cost minimisation).