Scientists reveal new orca insights

An orca combined with satellite tracking has allowed scientists to establish a clear path between Northland and Antarctica for one group of killer whales. File photo

Scientists have uncovered fascinating new insights about the commuting habits of Antarctic killer whales, finding that a specific group of orca are making regular trips between the frozen continent and comparatively warmer waters off the coast of Northland.

Dr Regina Eisert, of the University of Canterbury's Gateway Antarctica, led a research team during the last Antarctic summer which looked at patterns of the killer whales as part of a wider research programme on the Ross Sea.

Most of the killer whales found near Scott Base were found to belong to a group called Type-C, which are common in the Ross Sea and thought to prefer fish prey, including Antarctic toothfish.

"We wanted to determine whether a decline in the toothfish fishery in the Ross Sea poses 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 deployed satellite transmitters on killer whales 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 that Type-C killer whales were commuting between Scott Base and the waters off Northland in New Zealand.

University of Canterbury student Ekaterina Ovsyanikova discovered that one particular female Type-C killer whale had been photographed repeatedly in New Zealand and in McMurdo Sound, Antarctica.

"This suggested that the killer whale had been commuting between Scott Base and Northland," Dr Eisert said.

Satellite data received by Dr Lauriano and Dr Panigada showed that the whales swam due north towards New Zealand, confirming beyond a doubt the findings suggested by the earlier photo-identification.

"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 renowned orca expert Dr Ingrid Visser, who has been collecting Antarctic killer whale images for decades, as well as Heritage Expeditions and staff and scientists at Scott Base to create the first open-access photo-ID catalogue for Antarctic killer whales from the Ross Sea to New Zealand.

Photo-identification is one of the main non-invasive research tools used to study killer whales and other cetaceans.

Subtle differences in colouration patterns, nicks on the dorsal fin, and scars on the whale's body uniquely identify each whale, allowing individual killer whales to be recognised wherever they go.

The compilation of whale images into a catalogue also allows scientists to follow individuals in time and space, and even estimate the total size of a population.