Killer Whales (Orcinus orca)

The killer whale is the largest member of the dolphin family, Delphinidae. Its size, striking black and white colouring and tall dorsal fin are the main identifying characteristics. Killer whales are mainly black above and white below, with a white oval eye patch, and a grey saddle patch below the dorsal fin. Each killer whale has a uniquely shaped dorsal fin and saddle patch, as well as naturally acquired nicks and scars. Individual killer whales are identified using photographs of the dorsal fin, saddle patch, and sometimes eye patches (Ford et al. 2000). They are sexually dimorphic.

Maximum recorded lengths and weights for male killer whales are 9.0 m, and 5,568 kg respectively, whereas females are smaller at 7.7 m and 4,000 kg (Dahlheim and Heyning 1999). The tall triangular dorsal fin of adult males is often as high as 1.8 m, while in juveniles and adult females it reaches 0.9 m or less. In adult males, the paddle-shaped pectoral fins and tail flukes are longer and broader and the fluke tips curl downward (Bigg et al. 1987).

Currently, most authorities consider killer whales to be one species, Orcinus orca, having regional variations in diet, size, colouration, and vocal patterns (Heyning and Dahlheim 1988, Ford et al. 2000, Barrett-Lennard and Ellis 2001). Two and possibly three distinct species have recently been proposed for Antarctic populations (Mikhalev et al. 1981, Berzin and Vladimorov 1983, Pitman and Ensor 2003), but they are not yet widely accepted (Reeves et al. 2004). In addition, recent genetic studies report little global variation in mitochondrial DNA suggesting that the population segregation indicated by the morphological differences described above is relatively recent (Barrett-Lennard 2000, Hoelzel et al. 2002).

Three distinct forms, or ecotypes, of killer whale inhabit Canadian Pacific waters: transient, offshore and resident. These forms are sympatric but socially isolated and differ in their dietary preferences, genetics, morphology and behaviour (Ford et al. 1998, 2000, Barrett-Lennard and Ellis 2001).

Transient Killer Whales

Transient killer whales feed on marine mammals; particularly harbour seals (Phoca vitulina), porpoises, and sea lions (Ford et al. 1998). They travel in small, acoustically quiet groups that rely on stealth to find their prey (Ford and Ellis 1999). To the experienced eye, the dorsal fins of transient whales tend to be pointed and their saddle patches are large and uniformly grey (Ford et al. 2000).

Offshore Killer Whales

Offshore killer whales are not as well understood as residents and transients, but they are thought to feed on fish (Ford et al. 2000, Heise et al. 2003). They travel in large acoustically active groups of 30 or more whales, using frequent echolocation and social calls (Ford et al. 2000). The dorsal fins of offshore killer whales are more rounded than those of transients, and their saddle patches may either be uniformly grey or may contain a black region.

Resident Killer Whales

Resident killer whales are the best understood of the 3 ecotypes. They feed exclusively on fish and cephalopods and travel in acoustically active groups of 10 to 25 or more whales (Ford et al. 2000). The tips of their dorsal fins tend to be rounded at the leading edge and have a fairly abrupt angle at the trailing edge. Their saddle patches may be uniformly grey or contain a black region.

The social organization of resident killer whales is highly structured. Its fundamental unit is the matriline, which comprises a matriarch, her offspring, and the offspring of her daughters. Both sexes remain within their natal matriline for life (Bigg et al. 1990). Social systems in which both sexes remain with their mother for life has only been described in one other mammalian species, the long-finned pilot whale, Globicephala melas (Amos et al. 1993). Bigg et al (1990) defined pods as groups of closely related matrilines that travel, forage, socialize and rest with each other at least 50% of the time, and predicted that pods, like matrilines, would be stable over many generations. However, Ford and Ellis (2002) showed that inter-matriline association patterns in the northern residents have evolved over the past decade such that some of the pods identified by Bigg et al. now fail to meet the 50% criterion. Their analysis suggests that pods are best defined as transitional groupings that reflect the relatedness of recently diverged matrilines.

Each resident pod has a unique dialect made up of approximately a dozen discrete calls (Ford 1989, 1991). These dialects can be distinguished, providing each pod with a unique acoustic signature. Dialects are learned from mothers and other associated kin and are highly stable over time (Ford et al. 2000). Their function is not entirely understood, although it appears that they play an important role in mate selection (Barrett-Lennard 2000). Despite having distinct dialects, some pods share certain calls and call variants. Pods that share one or more calls belong to a common clan.

Resident killer whales that share a common range and that associate at least occasionally are considered to be members of the same community, or population. There are two communities of resident killer whales in British Columbia, the northern residents, and the southern residents. They have not been observed interacting and genetic studies have revealed that the two populations rarely if ever interbreed (Barrett-Lennard and Ellis 2001). The northern resident community consists of three clans, and the southern resident community, one clan.

Additional Information

For further information on British Columbia's killer whales and other marine mammals please visit the Weblinks - Marine Mammal Science compiled by Jackie Hildering for marine education programmes.

Killer Whales Serve as Sentinels for Ocean Pollution

The proposed Recovery Strategy for the Northern and Southern Resident Killer Whales (Orcinus orca) in Canada.