Under The Microscope

Banks Peninsula Marine Mammal Technical Report, 1992, by various authors. Canterbury Conservancy Technical Report Series 4, July 1992, 84pp.

The name "Hector's dolphin" has become almost a household word since a study in the mid-1980s suggested that about a third of the population around Banks Peninsula had been killed by gillnet entanglement over a four-year period. They are now protected by a marine mammal sanctuary declared by DOC, and a seasonal ban on gillnetting.

Such appealing little dolphins are prime candidates for concern by many of today's conservationists ready to leap from their armchairs on to a bandwagon. Opposing the greenies, however, are the people of SNAG, the Set Net Action Group, who say the sanctuary unnecessarily and unfairly infringes their fishing rights.

DOC has now issued a report for the purposes of reviewing the sanctuary three years after its inception and, so far, science seems to be on the side of the greenies. The report sets out to present the findings of recent and earlier research -- aerial surveys of abundance, reports on dolphins washed up on Canterbury beaches, two studies of dolphin entanglement, and a review of the sanctuary. A summary of the original research identifying the problem, by Drs Stephen Dawson and Elizabeth Slooten, is also included.

The report is heavy going, with slim pickings for anyone after hard factual data. It is full of references to unspecified or unidentifiable errors in estimates of dolphin populations, numbers killed and the breakdown of accidental catch in commercial versus private fishermen's nets. There is no overall summary tying together all the data in plain language; important conclusions are widely scattered.

In many respects the report is a mess and feels as though it's been thrown together with undue haste, which is ironic since one of its major conclusions is that much more research is needed. A crucial table summarising numbers of dolphins killed over a 4-year period is gibberish (for example, 200 + 24 + 6 dead dolphins add up to 29230) and MAFFish's contribution on set-net entanglement was withdrawn at the last minute for "editorial reasons"; it has to be obtained separately.

MAF's report takes the dubious step of summarily disregarding data on dead dolphins found drifting or washed ashore, on the grounds that it is not possible to prove whether these were caught in amateur or commercial fishermen's nets. This data deserves fuller discussion as it seems more than a curious coincidence that three-quarters of those dolphins died during the Christmas-January holiday period, when amateur set-netting is likely to be at its peak.

What is clearly established now is that there are probably only a few hundred Hector's dolphins around Banks Peninsula, they have a low reproductive rate, stick close inshore during summer and don't move about a lot. The good news is that the dolphins don't seem to have dramatically declined in number since the sanctuary was declared.

Professor Euan Young's review of the sanctuary, perhaps the most helpful summary of the main issues, makes up the last eight pages of the report. In concluding that more research is needed, he adds that the scientists shouldn't have it all to themselves: that SNAG too has a worthwhile role to play in the ongoing studies.

Mike Bradstock

Mike Bradstock runs Canterbury University Press in Christchurch.