Key Points:

Four southern right whales have spent the past week romancing just off the coast south of Dunedin - and have been shot by the Department of Conservation for their trouble.

The whales frolicked 200m off Kuri Bush, near Taieri Mouth, yesterday, exciting conservationists who believe the pod could reintroduce the species to mainland New Zealand.

Marine biologist Simon Childerhouse, of Dunedin, said it was "highly unusual" to see such a large group so close to shore.

Mr Childerhouse yesterday took biopsies of the three males and one female, using a .22 calibre Paxarms biopsy rifle.

The rifle fires a plastic dart, which collects a small sample of tissue from the mammals. "It hardly hurts them at all," he said. "Sometimes they give a little flick of the tail, but that's about it."

The main population of southern right whales is at the Auckland Islands, where there are an estimated 1000 whales.

This was the "first ever report of a mating group on the mainland" and the biopsies were the first on southern right whales gathered this year, Mr Childerhouse said.

"It's very exciting. We can use this information to see if the population structure of southern right whales around New Zealand is the same as the Auckland Islands population."

The whales were named because they were "the right whale to hunt", Mr Childerhouse said.

"They were slow, coastal and floated when killed. They also had a high return in oil. They used to breed in Otago Harbour. Whalers used to just hang around in a cove and wait for them to turn up."

Adult southern right whales grow up to 18m long. "They're getting more and more common on the mainland than they have been for hundreds of years." Southern right whales can be distinguished by their black colour, v-shaped blowhole spray and white growths on their heads, called callosities. Each whale has a unique callosity pattern.

* Sightings should be reported to DoC on 0800 DOCHOT line (0800 36 24 68).