Pack Ice Killer Whales

Two Pack Ice killer whales surfacing. Photo provided by fournier.bapt.

Antarctic Type B1 killer whales, also known as Large Type B killer whales, or Pack Ice killer whales, are a large and pagophilic mammal-eating ecotype of killer whale that inhabits the dense pack ice of the Antarctic Peninsula, primarily known for their unique hunting technique, known as 'wave-washing.' According to current estimates, there's about ~102 individuals, with a declining trend in abundance (4.7% per year) and reduced apparent survival in recent years.

### Social Structure

Pack Ice killer whales are usually seen travelling in pods consisting of seven individuals in average, ranging from one to fourteen individuals.

### Common Physical Features

Pack Ice killer whales have a two-tone gray pigmentation, with the rostrum, pectoral fins, part of the dorsal fin, and flukes being darker than the rest of the body; body is chunkier and dorsal fin is taller than Gerlache killer whales. They have a dorsal cape that extends from the saddle to the post-ocular patch (eyepatch), it may have a narrow 'white border' on its sides. The eyepatch is large and wide, more extensive than Type B2 (Gerlache) killer whales, and likely twice as large as Antarctic (type A) killer whales. They often show a yellow-brownish cast due to the presence of Diatoms on its skin. Flanks are narrow, a trait also observed in Gerlache (type B2) and Ross Sea (type C) killer whales.

Males can reach 7,5m (24.6ft) in average, with a maximum size of ~8m (26.2ft); females reach in average 6,9m (22.6ft) to a maximum size of 7,3m (23.9ft) dorsal fin is taller than Gerlache killer whales.

### Diet

The diet of Pack Ice killer whales is made up entirely of marine mammals, mainly ice seals. Their prefered prey is the Weddell Seal *(Leptonychotes weddellii),* they often tend to avoid Leopard Seals *(Hydrurga leptonyx)* and Crabeater Seals *(Lobodon carcinophagus),* however, predation also have been documented; though they have also been observed preying on Minke Whales *(Balaenoptera bonaerensis)* and possibly taking on Humpback Whales *(Megaptera Novaeangliae)*.

## Migration and Dive Depth

Pack Ice killer whales are found year-round in the coastal waters of the Western Antarctic Peninsula, having a circumpolar distribution, but they migrate to lower latitudes in a short amount of time, in order to shed their diatom-covered skin that accumulated on Antarctic waters. They have been recorded traveling to Australia and New Zealand, and far offshore from East side of South America. Mean dive depths for two Pack Ice killer whales were 36.1 and 42.5m, with maximum dives of 552 and 712m.

## References

1. ↑ Fearnbach, Holly & Durban, John & Ellifrit, David & Paredes, Alyssa & Hickmott, Leigh & Pitman, Robert. (2021). A decade of photo‐identification reveals contrasting abundance and trends of Type B killer whales in the coastal waters of the Antarctic Peninsula. Marine Mammal Science. 38. 10.1111/mms.12846.
2. ↑ Durban, J. & Fearnbach, Holly & Burrows, Douglas & Ylitalo, Gina & Pitman, R.. (2016). Morphological and ecological evidence for two sympatric forms of Type B killer whale around the Antarctic Peninsula. Polar Biology. 40. 10.1007/s00300-016-1942-x.
3. ↑ 3.0 3.1 3.2 Pitman, Robert & Ensor, Paul. (2003). Three forms of killer whales (Orcinus orca) in Antarctica. J Cetacean Res Manage. 5.
4. ↑ Durban, JW & Fearnbach, Holly & Paredes, A & Hickmott, Leigh & LeRoi, DJ. (2021). Size and body condition of sympatric killer whale ecotypes around the Antarctic Peninsula. Marine Ecology Progress Series. 677. 10.3354/meps13866.
5. ↑ https://www.jstor.org/stablSiniff, D. B., & Bengtson, J. L. (1977). Observations and Hypotheses concerning the Interactions among Crabeater Seals, Leopard Seals, and Killer Whales. *Journal of Mammalogy*, *58*(3), 414–416. https://doi.org/10.2307/1379341e/1379341
6. ↑ Savenko, Оksana. (2022). Winter records of killer whales (Orcinus orca) in the waters of the Wilhelm archipelago, West Antarctica. Theriologia Ukrainica. 2022. 210-215. 10.15407/TU2417.
7. ↑ Pitman, Robert & Durban, John. (2012). Cooperative hunting behavior, prey selectivity and prey handling by pack ice killer whales (Orcinus orca), type B, in Antarctic Peninsula waters. Marine Mammal Science. 28. 16 - 36. 10.1111/j.1748-7692.2010.00453.x.
8. ↑ Durban JW, Pitman RL. Antarctic killer whales make rapid, round-trip movements to subtropical waters: evidence for physiological maintenance migrations? Biol Lett. 2012 Apr 23;8(2):274-7. doi: 10.1098/rsbl.2011.0875. Epub 2011 Oct 26. PMID: 22031725; PMCID: PMC3297399.
9. ↑ Pitman RL, Durban JW, Joyce T, Fearnbach H, Panigada S, Lauriano G. Skin in the game: Epidermal molt as a driver of long-distance migration in whales. *Mar Mam Sci*. 2020; 36: 565–594. https://doi.org/10.1111/mms.12661