The killer whale is familiar to us all due in part to its popularized appearance in media attractions, like Shamu from Sea World. However, there has been much debate over how many species of these whales actually exist in the worlds oceans.
The killer whale,
Orcinus orca, is the only species formally accepted at this time. However, not the only one described.
Orcinus nanus was described in 1981 and
Orcinus glacialis was described in 1982, both by Soviet researchers.
O. nanus was based on body measurements with no maintained holotype, while
O. glacialis was based on at least 6-specimens, unfortunately the holotype and paratypes were later discarded .
Later three (3) subcategories of killer whales were broken out based on observed specimens as well as photographic evidence.
Type A – the classic killer whale that inhabits the open Antarctic waters, primarily feeding on minke whales
Type B – gray, black and white form that lives in the loose pack ice areas and feeds primarily on pinnipeds.
Type C – gray, black and white form that lives in the hard pack ice and feeds primarily on fish.
Each of these types varies in eye patch coloration as well, leading researchers such as Pitman and Ensor to speculate that type B and C may well be distinct species based on ecological and morphological differences.
Recently researchers R.L. Pitman, W.L. Perryman, D. LeRoi and E. Eilers took the task on of evaluating the whales, and have thus had their paper “A dwarf form of killer whale in Antarctica” published in the
Journal of Mammalogy 88 (1): 43-48, 2007.
The researchers conducted helicopter flights, 10 in total, starting in January 2005. Taking images from 8 of the flights, the researchers collected 252 images of unique specimens. The Type C specimen was the only one observed during the flights, and 220 of the images were viable for measurement analysis.
The results suggest that the Type C specimens are distinctly smaller than Orcinus orca, being up to 50% smaller in size. While the results do not support these whales being a distinct species, they are suggestive of a reproductive isolation of the Type C wherein adult females Type A’s are an average 0.8 metres larger than adult Type C males, making it less likely the female would mate with the smaller male.
The researchers do not go as far as stating these Type C whales are new species, rather suggest that additional morphological and genetic analysis must be done to determine whether a secondary species exists in the Antarctic waters. Until then one can only speculate that at a minimum there are at least two distinct groupings of whales, with the Type B category being either a potential third group, or a grouping of mixed Type A’s and Type C’s.
Labels: exploration, whale