A Study in Black and White

Here's a neat shot from Resurrection Bay, in southcoastal Alaska:

Orca (Orcinus orca), Resurrection Bay, AK 8/4/2012

These are, of course, Orcinus orca, or Killer Whales. Here's a couple more shots:

Orca (Orcinus orca), Kenai Fjords NP, AK 8/6/2012

Orca (Orcinus orca), Kenai Fjords NP, AK 8/6/2012

These were, according to our boat captain, so-called resident Orcas, preying mostly on Salmon. There are two other ecotypes of Orca in the NE Pacific, transient and offshore. The transient whales (well, big dolphins in fact) feed primarily on marine mammals, dolphin, porpoises, and especially seals. The offshore ones feed largely on sharks and other offshore fish. (1) This dietary specialization has impacts on precisely where you're likely to find each type, as well as on the sizes of their pods and subsequently on their social structures. (2) It's quite likely, according to the IUCN, that the species will be split in some fashion in the near future, so for the moment they haven't evaluated them. (3)

As if 3 overlapping species in one part of the ocean weren't enough, we find the same scenario in Antarctic waters, where three visually distinctive types feed on, respectively, Southern Minke Whales, seals, and toothfish. (4) A fourth type, just recently described, appears to feed on toothfish as well. (5)

I haven't found any discussion of distinct ecotypes in the Atlantic, but Orca are generally harder to find in Atlantic waters, so they're not nearly as well known there. Where they are commonly found, though, the resident forms at least are relatively easy to study (for whales, anyways) -- they're big, quite visible, and use fairly small home ranges where they can be seen quite frequently. Despite that, we're still not even sure how many species we have of these fascinating animals.

(1) Baird, R.W. 2000. The killer whale: Foraging specializations and group hunting. pp. 127-53. In: J. Mann, R.C. Connor, P.L. Tyack and H. Whitehead (eds.) Cetacean Societies. University of Chicago Press, Chicago. 433pp.

(2) Heimlich-Boran, J. R. (1988). Behavioral ecology of killer whales (Orcinus orca) in the Pacific Northwest. Canadian Journal of zoology, 66(3), 565-578.

(3) Taylor, B. L., Baird, R., Barlow, J., Dawson, S. M., Ford, J., Mead, J. G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R. L. (2008). 'Orcinus orca'. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 2009-01-01.

(4) Pitman, R. L., & Ensor, P. (2003). Three forms of killer whales (Orcinus orca) in Antarctic waters. Journal of Cetacean Research and Management, 5(2), 131-140.

(5) Pitman, Robert L.; Durban, John W.; Greenfelder, Michael; Guinet, Christophe; Jorgensen, Morton; Olson, Paula A.; Plana, Jordi; Tixier, Paul; Towers, Jared R. (2010). "Observations of a distinctive morphotype of killer whale (Orcinus orca), type D, from subantarctic waters". Polar Biology 34 (2): 303–306.