Ross Sea killer whales
Orcas, or killer whales, are found in every ocean, but are most abundant in the Southern Ocean with their population estimated to be between 25,000-27,000. This makes killer whales the third most abundant cetacean in Antarctica.
During the polar expeditions of the first decade of the 20th century, British biologists categorised the killer whale as the most common cetacean in the Ross Sea. When the expedition ships moved along the pack ice edge near the Victoria Land coast and around Ross Island during January and February the killer whales were observed near the ship almost every day.
Killer whales 101
Killer whales are distinctive in appearance with a large black body, a white underside and a water patch above and behind the eye. They also have a grey patch behind the dorsal fins. Killer whales are fast swimmers with speeds recorded up to 54km/h. Male killer whales can be up to 10m long with a tall dorsal fin that can be nearly 2m in height. Female length is around 20% less and they have a curved dorsal fin that is less than half the height of the males.
These enormous sizes make killer whales the largest of the dolphins and are one of the world’s most powerful predators feeding on mammals including seals, sea lions, and even whales with four inch-long teeth.
Killer whales hunt in pods comprising up to 40 individuals. There appear to be both resident and transient pod populations with resident pods preferring fish while transient pods target marine mammals. All pods use cooperative hunting techniques similar to wolf packs. Each pod has their own distinctive noises that its members can recognise. Killer whales use echo-location to communicate and hunt, making sounds that travel through the water until they hit and object and bounce back, revealing the object’s location, size and shape.
Types of Antarctic killer whales
On your Antarctica cruise you may encounter several types of killer whales/orcas in the Antarctic waters:
- Type-A are large orcas – up to 9.5m long – and prefer to live in open waters of the Southern Ocean, feeding mostly on minke whales.
- Type-B are Pack Ice orcas and are smaller than Type-A, feeding on Weddell seals they knock off ice. This is done by the whales cooperating together in the use of their tails and bodies to create waves that wash seals off ice floes. There is also a smaller variant of Type-B orcas: Gerlache orcas, named after the Gerlache Strait off the Antarctic Peninsula. Their preferred diet is unknown but they have been seen feeding on penguins and are usually spotted around penguin colonies.
- Type-C are known as Ross Sea killer whales, a dwarf species that is the smallest of the three known Antarctic types with males reaching around 6m in length. Ross Sea killer whales are typically seen off Eastern Antarctica in thin pack ice.
Different types of Antarctic killer whales confirmed
Killer whales from different eco-types don’t breed with one another: a criterion for being classified as a different species. However, until recently scientists had not proved these different species of orcas in Antarctica existed as researchers had not mapped the entire genome of the whales’ mitochondria, which houses DNA.
However, in 2013 scientists, after sampling 139 killer whales from the North Pacific, North Atlantic and the oceans surrounding Antarctica, were able to see clear differences between each species with Antarctic Type-B and –C species distinct from Type A and each other. The researchers believe that Type-B and –C are genetically similar because their lineage diverged from other orcas around 150,000 years ago – just a few years ago in evolutionary terms.
Ross Sea killer whales and their diet
The Type-C killer whale is thought to have a specialised fish diet, however the importance of Antarctic toothfish as a prey of these killer whales is unknown. There has been circumstantial evidence that suggests toothfish are an important prey for Type-C killer whales in the Ross Sea as the killer whales near McMurdo Sound have been commonly observed carrying toothfish in their mouths.
In addition, a comparison of the relative nutrient density of toothfish with other prey shows that toothfish represent a high-energy food resource of much higher quality than other potential prey in the Ross Sea region: Densities of alternative potential prey appear to be too low to justify killer whales coming to the Ross Sea for feeding and developing a fish-eating killer whale type.
Finally, scientists do not know the extent that toothfish forage or how deep Type-C killer whales can dive, though, in earlier studies it was estimated they dive to 200-400 m with a maximum of around 700m.
To understand more about the Ross Sea killer whale the GEMM Lab of Oregon State University has been collaborating with New Zealand scientists from the National Institute of Weather and Atmosphere (NIWA) and Gateway Antarctica of the University of Canterbury, to collect ecological data on Type-C killer whales in the Ross Sea.
During a pilot project in McMurdo Sound in the Ross Sea during January 2014 researchers recorded and photographed three observations of the killer whales with Antarctic toothfish prey. With these observations occurring during the late summer break-up of the fast ice over shallow coastal waters the scientists hypothesise that toothfish is the main prey for the Type-C killer whale, at least during the summer months.
Ross Sea killer whales commuting between Antarctica and New Zealand
Meanwhile, New Zealand and Italian scientists have discovered that Type-C killer whales swim 4,900 km from Antarctic to Northland: the top of New Zealand. Gateway Antarctica’s Dr Regina Eisert led a team to Scott Base during the 2014/2015 Antarctic summer that studied killer whales as part of a research programme on the Ross Sea ecosystem involving NIWA, Landcare Research and Lincoln University. The aim of the study was to determine the importance of toothfish and where killer whales feed in the Ross Sea.
At the same time 360 km north of Scott Base, Italian whale experts Dr Giancario and Dr Simone Panigada used satellite transmitters on killer whales in Terra Nova Bay to determine the killer whales’ movements. Dr Eisert said the two teams ‘’hit research gold’’ when they independently verified that Type-C killer whales were making long journeys between Scott Base and warmer waters off Northland, New Zealand.
One researcher, Ekaterina Ovsyanikova, found the same female Type-C killer whale had been photographed numerous times in New Zealand and McMurdo Sound, Antarctica. The research team found the average commute taking 22 days.
Digital database to track Ross Sea killer whales
The scientists from New Zealand are now aiming to collaborate with Dr Ingrid Visser from the Orca Research Trust as well as other researchers to create the first open-access photo-ID catalogue for Antarctic killer whales from the Ross Sea. Photo-identification is the main non-invasive research tools used to study killer whales. Slight differences in colour, nicks on the fins 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 catalogues will enable all researchers to follow individuals in time and space and make estimations of their total population size. Dr Visser is investigating the possibility of hosting a killer whale photo-ID on Antarctica New Zealand’s new digital asset management platform launched in June 2015. This database, created by a Wellington-based technology company NZMS, is based on a non-hierarchical network structure similar to the human brain, providing a matrix to curate, using and growing the killer whale photo-ID catalogue.