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Proceedings of the First Symposium on Marsupials in New Zealand

Topic 9: Possums On Offshore Islands

page 267

Topic 9: Possums On Offshore Islands

FALLA. In discussion on 1080 control and funding of research in general I made reference to the high costs of some of the research projects. There is also room for encouraging smaller individual projects, which would just need a little sympathetic encouragement rather than heavy financial backing. I am thinking particularly of a point arising from Dr Tyndale-Biscoe's address; he asked whether there was any indication that discrete populations of possums were settling to levels of stability well below the sustaining capacity of the environment. I do have the impression that the very interesting study that is going on at Kapiti Island* is likely to provide quite useful information on this aspect at the end of 5 or 6 years' work. This is being done at the request of the Lands and Survey Department's District Office in Wellington, who are responsible for Kapiti Island's welfare; it is also being done against a very steady pressure to stop the research altogether, and to get on with the job of exterminating the possums on the island. I think there is some room for encouragement of research of this kind, and discouragement of well-meaning but otherwise quite misdirected criticism of the work going on in the Kapiti sanctuary.

On Codfish Island, which I have visited two or three times over a long period of years, there are possums but there has been quite a considerable improvement in the general appearance of the vegetation; you find from the files that John Bamford's reports of the early 1950's indicate that there was no substantial sign of any increase in possums and certainly no significant damage. I suspect that if a follow-up study was now carried out it would be found that there are even fewer possums; I do not think anybody other than the prejudiced could feel that possums were doing any harm at all on Codfish. Now that too would seem to be the sort of place in which a single investigator could go, with little more than a technical assistant, and do quite a useful individual study.

GREEN. I agree with Sir Robert Falla's point regarding long term stabilisation between possums and their various habitats. I think this is the long term sort of work that should certainly be carried out in a variety of habitats. I wonder though whether the results you would get from a place like Codfish Island would be applicable in other habitats in New Zealand.

page 268

Elsewhere there may be far more diverse habitats, with pasture, willow, pole plantings, and so on; it could well be that the results from Codfish may not be terribly useful in other areas of the country, given the plasticity of Trichosurus vulpecula.

HARPER. I would like to comment briefly on this. I am planning a trip to Codfish Island to look at the sea birds. I would welcome somebody to join the party to look at possums.

PRACY. Further to Sir Robert Falla's comments, in about 1972 there was a survey party on Codfish Island which included John Bamford and myself. What Sir Robert anticipated was precisely the case. Peak populations there occurred about 1948; there is photographic evidence and reports to substantiate this. There were two types of assessment. Results suggest there has been a generally very light and scattered population from 1948; in the lower kamahi belt and in the damaged rata-kamahi forest there was what you would call a heavy or dense population. You did have forest mortality but you also had a lot of forest recovery.

* See BELL, B.D. & ATKINSON, I.A.E. 1976. Opossum research on Kapiti Island. Forest and Bird 199: 12–17.