The dynamics of possum (Trichosurus vulpecula Kerr) populations controlled by aerial poisoning
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
In 1947 legal protection was removed from the introduced Australian brush-tailed possum (Trichosurus vulpecula Kerr) changing its status from an animal valued for its fur to that of introduced pest. Although a considerable amount of overseas exchange had been won by the sale of skins (Pracy, 1962), the damage inflicted en exotic and indigenous vegetation had become so pronounced that the animal's advantages were far outweighed by its disadvantages. Much has been written of the deleterious effect of possums on vegetation but the real effects were not to become noticeable for some considerable time. Kirk (1920) and Cockayne (1926), both ecologists of some note, considered that apart from occasional damage suffered by orchardists the animal was giving little cause for concern and in fact "probably makes a valuable contribution to the diversity of New Zealand forests". In 1951 the Department of Internal Affairs, recognising that widespread control measures were necessary and that with current staff levels and commitments it could not undertake control operations on a satisfactory scale, introduced, as an interim measure, a national bounty scheme. Under this scheme the Dept. of Internal Affairs, and later the Forest Service, paid 2s.6d. (now 25c) for every pair of ears with a 9 x 2 inch strip of fur attached. In 1956, with the passing of the Wildlife Amendment Act (1956) and the Noxious Animals Act (1956), responsibility for the control of possums was passed from the Dept. of Internal Affairs to the New Zealand Forest Service. Over the following four years the service prosecuted extensive poison trials, ultimately to accept aerially sown carrot and manufactured pellet baits treated with sodium monofluoroacetate (1080) as a means of reducing and controlling possums in large areas of indigenous forest. The national possum bounty scheme was discontinued in 1960, after payment of some $2,000,000 since its inception some nine years earlier. Because of increasing concern over the effect possums were said to be having on the production of some pastoral lands, authority was given in the Rabbit Amendment Act (1960) for rabbit boards to undertake control work against the species in these areas. The Forest Service retained its responsibility for control of possums in State Forests, National Parks, Unoccupied Crown Lands and other non-rateable areas.