Marine mammal specialists from the University of Otago, Otago Museum and Doc take a look at a spectacled porpoise which washed up on Pipikaretu Beach. They are (from left) Carolina Loch, Emma Burns, Sophie White, Trudi Webster (obscured), Jim Fyfe, Associate Prof Liz Slooten (obscured), Prof Ewan Fordyce and Prof Steve Dawson. Photo by Peter McIntosh.

Dunedin marine mammal researchers have a new sense of purpose after a rarely seen porpoise washed ashore on Otago Peninsula.

A 2.15m-long male spectacled porpoise, one of the world's most rarely seen marine mammals, was found on Pipikaretu Beach by Penguin Place guide Tama Taiti on Wednesday morning.

It was taken to the Department of Conservation's workshop in Kaikorai Valley Rd, Dunedin, and a group of excited marine mammal specialists were invited to view it yesterday morning.

University of Otago geologist Prof Ewan Fordyce said fewer than 10 spectacled porpoises had washed ashore on New Zealand's coast and it was the first his research team had seen.

''It's a pretty important opportunity to help us understand the biology of a rare animal,'' he said.

By carrying out a postmortem, it might be established how it died, what it had fed on and where it had been.

The porpoise had been bitten by a large shark. It was not clear whether the porpoise was alive when the shark bit it.

''They are open-ocean animals - they live thousands of kilometres out at sea and we hardly ever see them. So when one is close to the shore we think something has gone wrong. Maybe it has got disoriented; maybe it has got a disease or a parasite.''

Prof Fordyce was present when the porpoise was put through a CT scanner at AgResearch's Invermay campus yesterday afternoon.

Marine biologist Prof Steve Dawson said out-of-proportion dorsal fins made male spectacled porpoises unique.

''It's completely outside any expectation you would have. Proportionally, it's probably the largest dorsal fin in the animal kingdom,'' Prof Dawson said.

Nobody knew why the dorsal fins were so large, but by dissecting it they might be able to get some idea.

It is the only species of porpoise which swims in New Zealand's waters.

Marine scientist Associate Prof Liz Slooten said she would contact scientists from Massey University and the University of Auckland, who would be ''very excited'' and might come to Dunedin to help with research.

The species was mostly associated with the Southern Ocean and New Zealand was ''right at the northern limit'' of its range.

Department of Conservation biodiversity ranger Jim Fyfe said another spectacled porpoise washed ashore near Timaru earlier this year and was in storage at Otago Museum.