New Zealand and Italian researchers have finally confirmed what scientists have suspected for nearly 20 years - that some of the orca seen around the coast of Northland are in fact orca from Antarctica.
The clincher is photos of the same female orca, taken in both Northland and Antarctica.
Dr Ingrid Visser, from the Orca Research Trust, has studied orca for more than 20 years. She knows most of the 200 or so animals that make up the small New Zealand population by sight.
But, every so often, she sees smaller orca with yellowish white patches and distinctive slanted eye patches - which she suspected were a kind of Antarctic orca.
Dr Visser has been collaborating with Dr Regina Eisert from Gateway Antarctica at the University of Canterbury over the photo identification of orca in New Zealand and Antarctica.
Ekaterina Ovsyanikova, a student supervised by the pair, recently struck gold, finding that the same individual female "Type C" orca 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.
For the past two summers, Dr Eisert has been researching orca and their diet in the McMurdo Sound area of the Ross Sea as part of the Top Predator Alliance (TPA) project.
At the same time, Italian researchers Dr Giancarlo Lauriano, from the Institute for Environmental Protection and Research, and Dr Simone Panigada from the Tethys Research Institute, have been studying Type C Antarctic orca in Terra Nova Bay, 360 kilometres north of New Zealand’s Scott Base.
They deployed satellite transmitters on orca to determine where they travelled to, and these have revealed that Type C Antarctic orca are travelling to northern New Zealand, and as far as north as the Kermadec Islands, a journey of nearly 5000 kilometres.
The satellite tags only work for a month, and most of the data collected shows the whales moving north, so it's not yet known how frequently the orca make the return journey.
Orca in Antarctica: Type A to Type C
There are three types of orca recognised in Antarctica. Type A are found in open water around the Antarctic Peninsula and migrate there in summer from further north to prey on Antarctic minke whales. Type B live in loose pack ice and prey mainly on seals. Type C are the smallest and least well-known type, and they forage deep into the pack ice, hunting fish such as Antarctic toothfish in open-water leads amongst the ice.
These are the orca that are being studied in the Ross Sea.
“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.
She said that the the whales’ long commute "would also suggest that there is much greater ecological connectivity between Antarctica and New Zealand than previously thought".
The TPA, of which this work forms a part, is a joint multi-year research programme between Gateway Antarctica, NIWA, Landcare Research and Lincoln University. It is looking at top predators in the Ross Sea ecosystem, including Weddell seals, Adelie penguins and Antarctic toothfish, as well as orca.
“We wanted to determine whether a decline in the Antarctic 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.
She said that, although scientists had suspected that Type C orca eat Antarctic toothfish, as well as smaller fish such as silverfish, it was during the 2013/14 summer that the research team finally got photographic evidence of an orca with a toothfish in its mouth.
While some researchers had reported declines in the number of toothfish caught in McMurdo Sound, the TPA has been finding evidence of good numbers of toothfish coming into the sound.
The Antarctic Type C orca have learnt to use the open water provided in the shipping channel created by an icebreaker each summer in McMurdo Sound.
“Killer whales are very smart,” Dr Eisert said. “You have to remember they are about the same size as an elephant and they have a kilogram more [of] brain. They wait for the ship to come in and then they follow the channel right down to [McMurdo] Station.”
The TPA project has also been collecting photos of as many Antarctic orca as possible to add to Dr Visser’s existing photo identification catalogue for New Zealand orca.
Photo identification is one of the main non-invasive research tools used to study orca, as well as other whales, dolphins and sharks. 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.
Compilation of whale images into a catalogue allows scientists to follow individuals in time and space, and even estimate the total size of a population.
Dr Eisert is currently working with Antarctica NZ to investigate the possibility of hosting the orca photo identification catalogue on Antarctica NZ’s new digital asset management platform.
Small tissue samples, collected using a biopsy dart fired from a special gun, will allow the researchers to analyse diet, and confirm how important Antarctic toothfish are as food.
The findings are being presented this week at a meeting of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).
They are the result of international collaborations between Gateway Antarctica at the University of Canterbury, Italian researchers from the Institute for Environmental Protection and Research and the Tethys Research Institute, the Orca Research Trust and Heritage Expeditions - a Christchurch-based adventure travel company.
Many citizen scientists in Antarctica and New Zealand contributed their killer whale photos and sightings.
In New Zealand, Antarctic killer whale research is supported by the Ministry of Primary Industries, Antarctica New Zealand, the New Zealand Antarctic Research Institute and Canon New Zealand Ltd.