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Proceedings of the First Symposium on Marsupials in New Zealand

Introduction

Introduction

If control of the common brushtail possum Trichosurus vulpecula on farm land is to be economic, the cost of control should not exceed the value of the damage (reduction in yield) caused by possums. Thus, assessment of the economic impact of possums is a pre-requisite for economic control. This was recognised by the Technical Advisory Committee (Animal Pests), which stated in 1969 that "while there is no evidence that opossums compete seriously with livestock for pasture on a wide scale, locally opossum grazing can appear serious enough for farmers to persuade pest destruction boards to carry out intensive control. The effects of opossums on pasture should therefore be investigated before such intensive control can be justified" (Anon 1969). This is even more crucial today because of the ever-increasing costs of control operations.

As a preliminary to any cost/benefit analysis of possum control on agricultural land, it is necessary to devise methods of measuring the damage (ultimately in terms of the market value of the units lost) and the cost-effectiveness of control. In this presentation we give:

page 198
1.A brief review of previous reports of possum damage to farm crops and pasture;
2.An outline of the methods and problems of measuring the damage; and,
3.An outline of the problems of assessing the cost-effectiveness of control.