A scientific team from Italy and another from University of Canterbury have independently proven orca move between the Antarctic and Northland.
Dr Regina Eisert, from Canterbury's Gateway Antarctica, led a team at Scott Base that studied orca as part of a larger research programme on the Ross Sea ecosystem.
Orca in Antarctic waters are known as the type-C species, which is smaller but more common and lives in larger groups than Northern Hemisphere species.
"We wanted to determine whether a decline in the toothfish fishery in the Ross Sea posed a risk to type-C killer whales, including finding out how many there are in the Ross Sea and where they feed," Dr Eisert said.
At the same time, about 360km north of Scott Base, Italian whale experts Dr Giancarlo Lauriano and Dr Simone Panigada fixed satellite transmitters to orca in Terra Nova Bay to determine the whales' movements.
Dr Eisert said the two teams from New Zealand and Italy hit "research gold" when their results independently verified the orca were commuting between Scott Base and the waters off Northland.
University of Canterbury student Ekaterina Ovsyanikova, whose work is supervised by Dr Eisert and Northland-based orca expert Dr Ingrid Visser from the Orca Research Trust, discovered that the same female Type-C killer whale had been photographed repeatedly in New Zealand and in McMurdo Sound, Antarctica.
"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.
"The whales' long commute would also suggest that there is much greater ecological connectivity between Antarctica and New Zealand than previously thought."
Dr Eisert has teamed up with Dr Visser, Heritage Expeditions which has ships in the Antarctic and Scott Base personnel to create the first open-access photo-ID catalogue for orca from the Ross Sea to New Zealand.
Photo-identification is one of the main non-invasive research tools used to study orca, whales and dolphins.
Subtle differences in colouration patterns, nicks on the dorsal fin, and scars on the body uniquely identify each one.