Type D Killer Whales

A Type D killer whale surfacing. Photo provided by TAAF-MNHN-CEBC.

Antarctic type D killer whales, also dubbed as 'Sub-Antarctic' killer whales, are the most unknown killer whale ecotype in the world; They have an 'odd-looking' appearence, have a circumpolar distribution in the sub-Antarctic seas, being documented for the first time in history in New Zealand, on Paraparaumu beach (1955).

## Pod size

Group size of these killer whales is relatively large, having between 10 - 35 individuals.

## Common Physical Features

Sub-Antarctic type D killer whales have a typical black and white pigmentation; a rounded melon, quite similar to Pilot Whales; a small, paralel to the body axis eyepatch (that may be non-existent in some individuals), The relative size of the eye patch in type D is not obviously sex or age related because it appears to be of similar relative size in adult males and females, as well as in calves. The saddle is faint, but moderately conspicuous, in comparision to killer whales found in the tropics whose saddle patches are often barely discernable. Its dorsal fin is falcate shaped, narrow, pointy and usually quite back-swept. Average and maximum size of males is unknown, however, females average 5,7m (18.7ft) to a maximum size of 5,9m (19.3ft) . In addition, their teeth is also small, with a size of 8cm (3.1cm) to 10cm (3.9in) in lenght, in comparision, average killer whales' teeth is 12cm (4.7in) to 15cm (5.9in) in lenght.

## Diet

Most of the diet is unknown, however, researchers photographed these whales feeing on Patagonian Toothfish (Dissostichus eleginoides) from comercial longline vessels at Crozet Islands, in southern Indian Ocean.

## Distribution

These killer whales are found in latitudes between 40°s to 60°s, they have an circumpolar distribution and are found in offshore waters, they were observed for the first time in New Zealand, and other sightings were recorded in Cape Horn (Chile), the Crozet islands, Marion islands, etc.

## Strandings

On May 13, 1955, 17 killer whales stranded on Paraparaumu Beach, north of Wellington. Two skulls were preserved from the stranding event along photographs of the whales in Te Papa Museum.

In November 2022, for the first time in history, and after 67 years since the first documented stranding, nine subantarctic killer whales stranded on the coast of the Strait of Magellan, Chile. A total of eight females (four adult females, two juveniles), two females and one male of undetermined age. On November 4th, the stranding of a killer whale was reported in Bahía Posesión, in north-east Magellan Strait. Ofcials from the National Fisheries Service (SERNAPESCA) and the Rio Seco Natural History Museum (MHNRS) visited the stranding event the same day. On November 9th, the remains of the killer whale were transferred to the Río Seco Natural History Museum in the city of Punta Arenas, where its skeleton is being prepared for further morphological description and will be part of the museum’s cetacean collection. On November 30th, SERNAPESCA was informed of the stranding of a group of cetaceans after a helicopter overfight at approximately 4.6 km east. MHNRS officials went to the site on December 3rd, finding other eight stranded killer whales in total.

## Inbreeding

In January 2019, NOAA scientists collected three biopsy samples from subantarctic killer whales in Cape Horn, Chile, being one of the most important biopsies for the study of these whales. The samples were studied by Dr. Andrew D. Foote and other colleagues. The results of the studies were published in 2022, determinating that the sub-Antarctic killer whales showed a poor genetic diversity, as genomes show among the highest level of inbreeding reported for any mammalian species (FROH ≥ 0.65).

## References

1. ↑ 1.0 1.1 1.2 Pitman, Robert & Durban, John & Greenfelder, Michael & Guinet, Christophe & Jorgensen, Morton & Olson, Paula & Plana, Jordi & Tixier, Paul & Towers, Jared. (2011). Observations of a distinctive morphotype of killer whale (Orcinus orca), type D, from subantarctic waters. Polar Biology. 34. 303-306. 10.1007/s00300-010-0871-3.
2. ↑ 2.0 2.1 2.2 Pitman, Robert & Ballance, Lisa & Sironi, Mariano & Totterdell, John & Towers, Jared & Wellard, Rebecca. (2019). Enigmatic megafauna: type D killer whale in the Southern Ocean. Ecology. 101. 10.1002/ecy.2871.
3. ↑ Newsome, Seth & Etnier, Mike & Monson, Daniel & Fogel, Marilyn. (2009). Retrospective characterization of ontogenetic shifts in killer whale diets via δ13C and δ15N analysis of teeth. Marine Ecology Progress Series. 374. 229-242. 10.3354/meps07747.
4. ↑ Tixier, Paul & Gasco, Nicolas & Duhamel, Guy & Guinet, Christophe. (2016). Depredation of Patagonian toothfish ( Dissostichus eleginoides ) by two sympatrically occurring killer whale ( Orcinus orca ) ecotypes: Insights on the behavior of the rarely observed type D killer whales. Marine Mammal Science. 32. n/a-n/a. 10.1111/mms.12307.
5. ↑ 5.0 5.1 Foote, Andrew & Alexander, Alana & Ballance, Lisa & Constantine, Rochelle & Muñoz, Bárbara & Guinet, Christophe & Robertson, Kelly & Sinding, Mikkel-Holger & Sironi, Mariano & Tixier, Paul & Totterdell, John & Towers, Jared & Wellard, Rebecca & Pitman, Robert & Morin, Phillip. (2023). "Type D" killer whale genomes reveal long-term small population size and low genetic diversity. The Journal of heredity. 114. 10.1093/jhered/esac070.
6. ↑ Pictures of the skull and teeth preserved by Te Papa Museum here.
7. ↑ Haro, Daniela & Blank, Olivia & Garrido, Gabriela & Cáceres, Benjamín & Cáceres, Miguel. (2023). Unraveling the enigmatic type D killer whale (Orcinus orca): mass stranding in the Magellan Strait, Chile. Polar Biology. 46. 1-7. 10.1007/s00300-023-03156-2.