New Zealand's great white sharks migrate to tropical waters off Australia and islands in the Pacific to feed on baby humpback whales, scientists say.

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After tracking tagged sharks using GPS, New Zealand fisheries scientists have concluded the giant ocean hunters appear to be regular winter visitors to tropical waters.

One of nine great white sharks to have GPS-linked tags attached this year, a 3.5m specimen nicknamed Thomas, migrated to Australia's Great Barrier Reef.

He turned up within 100km of where a 4.4m female great white, nicknamed Kerri, arrived last summer, setting a distance record for a New Zealand shark.

Both swam more than 3000km to the reef after being fitted with tags which record location, depth and temperatures.

The tags are set to pop off the shark and float to the surface to transmit data to a satellite linked to scientists' computers.

Other tags have popped up in New Caledonia, Vanuatu, and halfway to Tonga and these trans-oceanic migrations to tropical waters have changed perceptions of the sharks as cold water, coastal creatures.

"We think they may be searching for newborn humpback whale calves, because all tags have surfaced in or near known humpback calving sites," National Institute of Water and Atmospheric Research fisheries scientist Malcolm Francis said.

Because sharks tagged in Australia have also turned up in New Zealand waters, scientists think that white sharks in the southwest Pacific may comprise a single population.

The shark tagging was started in 2005.

Dr Francis said it had been a bumper year for tagging white sharks.

"Until this year we've only been able to tag six white sharks in three seasons of fieldwork," he said.

"This year has greatly added to our tally with three more being tagged at Stewart Island and six more at Chatham Islands.

He said two tags had failed but there were still six more tagged sharks in the water which were due to report between October and January "... offering us an amazing insight into the secret lives of these predators."

Previous tagged white sharks have dived as deep as 1,000 metres and encountered temperatures ranging from three degrees Celsius in deep water to 24 degrees in shallow tropical waters - a huge range in temperature which Dr Francis said was unusual among fish.