Emma Carroll talks about the return of southern right whales from the edge of extinction and a project asking the public to report whale sightings.

Researchers are using satellite tracking to find out where New Zealand's southern right whales, or tohorā, go when they leave their winter breeding hotspot at the subantarctic Auckland Islands.

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Tohorā used to be a common sight around New Zealand's shores. Then, commercial whaling took them to the edge of extinction.

The New Zealand southern right whale population plummeted to perhaps just 40 animals by 1920, from more than 30,000 before Europeans arrived in the late 18th century.

Since whaling ended and the whales have been protected their numbers have been climbing steadily. The most recent population estimate, from 2009, is about 2,000 whales.

The whales' main breeding ground is at Port Ross, in the Auckland islands, and researchers - who have been studying the population there for several decades - have counted up to 200 individuals there in winter, including 50 cow-calf pairs, in the large harbour's sheltered waters.

"It's not a big place. It's basically whale soup," says Rutherford Discovery Fellow Emma Carroll, from the University of Auckland.

Where do the whales go in summer?

Emma Carroll is currently leading an expedition to the Auckland islands, and one of the team's goals is to attach six satellite tags to find out where the whales go when they leave the breeding ground.

Only two tohorā have been successfully tagged and tracked prior to this, and the pair did very different things.

An adult male (tag number 96373) moved north from the Auckland islands to Stewart Island, stopped transmitting for a while and then turned up south of Western Australia.

The adult female (tag number 96374) headed west to feeding grounds along the subtropical convergence, south of Australia, where warm subtropical waters meet cooler subantarctic waters.

Public help needed to sight whales

Although right whales usually return to breed in the place they were born, meaning most animals return to the Auckland islands, Emma says that small numbers of right whales are also returning to mainland New Zealand.

She says there have been large groups seen off Southland, and two females have each given birth to two calves off northern New Zealand.

"Hopefully that's the beginning of that new knowledge of the mainland as a good place to come and have babies," says Emma…

Go to this episode on rnz.co.nz for more details