Dwarf Killer Whale Discovered in Antarctica
Posted by: Loren Coleman on November 6th, 2007
A new paper written by Robert Pitman of the NOAA Fisheries - Ecosystem Studies Program and his colleagues provides evidence that there is at least one new species of killer whale in Antarctica.
In a new 2007 issue of Journal of Mammalogy, the article’s following abstract summarizes their findings:
In the early 1980s, 2 groups of Soviet scientists independently described 1, possibly 2 new dwarf species of killer whales (Orcinus) from Antarctica. We used aerial photogrammetry to determine total length (TL) of 221 individual Type C killer whales—a fish-eating ecotype that inhabits dense pack ice—in the southern Ross Sea in January 2005. We confirmed it as one of the smallest killer whales known: TL of adult females (with calves)
averaged 5.2 m 6 0.23 SD (n 1⁄4 33); adult males averaged 5.6 6 0.32 m (n 1⁄4 65), with the largest measuring 6.1 m. Female Type A killer whales—offshore mammal-eaters—from Soviet whaling data in the Southern Ocean were approximately 1–2 m longer, and males were 2–3 m (up to 50%) longer (maximum length 9.2 m).Killer whale communities from the North Atlantic and in waters around Japan also appear to support both a smaller, inshore, fish-eating form and a larger, offshore, mammal-eating form. We suggest that, at least in Antarctica, this degree of size dimorphism could result in reproductive isolation between sympatric ecotypes, which is consistent with hypotheses of multiple species of killer whales in the Southern Ocean. Robert L. Pitman, Wayne L. Perryman, Don Leroi, and Erik Eilersa, “Dwarf Form of Killer Whale in Antarctica,” Journal of Mammalogy, 88(1):43–48, 2007.
In the paper, Pitman, et al. review the three ecotypes of killer whales from Antarctica based on field observations and photographs, designated as types A, B, and C:
Type A appears to be a ‘‘regular’’ killer whale: a large, black and white form with a medium-sized white eye patch. It inhabits open water in Antarctica and apparently feeds mainly on Antarctic minke whales (Balaenoptera bonaerensis). Type B is a gray, black, and white form with a dorsal cape and a very large white eye patch; it inhabits loose pack ice and appears to specialize in feeding on pinnipeds. Type C also is a gray, black, and white form with a dorsal cape, but it has a narrow, slanted eye patch; it lives in dense pack ice and apparently eats mainly fish. Based on consistent differences in morphology and ecology, and a lack of evidence for interbreeding among these at least partially sympatric forms, it was suggested that types B, C, or both may represent new species of killer whales.(Pitman and Ensor 2003).
These Type C killer whales are much different than the others, and breeding appears impossible now across Types A and B to C.
Pittman and his coauthors therefore state their “findings confirm the presence of at least one markedly smaller ecotype, which is consistent with hypotheses that more than one species occurs in the Southern Ocean.”
The bottomline is that a new dwarf killer whale appears to have been discovered, which aligns with previous physical findings by the Soviets.
Download the complete paper here: Dwarf Killer Whale
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Good stuff. Reproductive isolation and speciation is an interesting course of events. In this sort of case, the killer whales started to branch out to fill different ecological niches and exploit different rescources which led to gradual adaptations, for example a killer whale that specializes in hunting pinnipeds will start to develop features useful in this endeavor due to selective pressures. Adaptations to the new niche lead to morphological differences, which eventually leads to reproductive isolation and new species. To look at these three different killer whales and see the ways in which they have uniquely adapted to their respective lifestyles is very interesting to me.
Great article, I hope they don’t become part of a menu anywhere. The thing’s some people eat is beyond me.
Finally a paper of the third species of killer whale, Thanks for posting Loren.
There have also been reports of a brown variety of Killer Whale off the Gulf of Aden, Alaska. It is most commonly reported near the village of Alula.