Comments: Two forms of the killer whale occur in the coastal waters of North America from Washington to Alaska. The two groups, generally refered to as "transient" and "resident," differ in foraging behavior, habitat use, group dynamics, dorsal fin shape, pigmentation patterns, and mtDNA; apparently there is little or no gene flow between the two groups (see references in Baird et al. 1992). A third group consists of "offshore" killer whales.
Orcinus nanus and O. glacialis were described from antarctic waters in the early 1980s but, because of weak supporting evidence, these nominal species have not been accepted as valid by most authorities (O. nanus is a nomen nudum). Mead and Brownell (in Wilson and Reeder 1993, 2005) and Jones et al. (1992) regarded Orcinus as monotypic.