Killer whales from Antarctic are swimming as far as Northland, researchers have found.
Scientists from Canterbury University used photo-identification and Antarctic researchers from Italy used satellite transmitters to track the orcas in the 2014-2015 Antarctic summer.
"Subtle differences in colouration patterns, nicks on the dorsal fin, and scars on the whales body uniquely identify each whale, allowing individual killer whales to be recognised wherever they go," scientists say.
Gateway Antarctica scientist Dr Regina Eisert says the whales feed on prey including Antarctic toothfish and they wanted to determine whether the decline in toothfish posed a risk to the whales.
But the teams hit "research gold" with results independently verifying the killer whales were commuting between Scott Base and the waters off Northland in New Zealand - a distance of more than 4500km.
The photo-ID showed the same whale repeatedly in both places and the satellite data showed the whales swam due north towards New Zealand, she said.
"If Antarctic killer whales roam all the way from Scott Base to the North Island of New Zealand, rather than stay in a relatively confined area as some scientists believe, it crucially changes our understanding of the ecology of these key top predators and the potential threats they may face," Dr Eisert said.
It also suggests there is much greater ecological connectivity between Antarctica and New Zealand than previously thought, she said.
The research is part of a wider study on the Ross Sea ecosystem.
