Resource Economics of Exotic Mongoose Control

Abstract

Although it is possible to reduce the number of exotic species by 90%, we often say that we need enormous cost and labor to remove the remaining 10%. On the other hand, if it is not eradicated, it must be controlled forever. In this chapter, we introduce “economics of exotic species control,” including mongooses that are introduced into Amami Oshima Island, as an example. Regarding the control of fruit flies, there is a successful example of eradication from small islands by mass release of sterile males instead of capture by traps. The relationship between catch per unit effort (CPUE) and the population size (N) is important, and in many cases CPUE is a concave function of N. In this case, the total effort required for eradication will be infinitely large. CPUE-dependent population estimation involves uncertainty. By combining with a population dynamics model, the nonlinearity of the N-CPUE relationship can be estimated. In order to eradicate with a finite budget, we could expect eradication of the invasive species (1) if its natural population growth rate has the Allee effect, (2) if the population is induced to a sufficiently low density and accidental extinction due to demographic stochasticity, and (3) combining methods such as detection dogs and chemical spraying in addition to capture by traps. The Allee effect cannot be expected so much because a small number of invading individuals have increased and become established. In the case of maintenance at a low population density, it is unknowable when it will be extinct, but the management cost may be cheaper than eradication because the ecological impact is small when the population is small. Eradication may be possible in combination with other active methods. If eradication on Amami Oshima Island, which has an area of about 712 km², will be successful in the near future, this practice and its comprehensive analysis, including its cost-effectiveness, is valuable worldwide.