Killer Whales

Killer whales are distinctively marked black-and-white dolphins. They exist in British Columbia as three distinct assemblages (groups): residents, transients and offshores. Each assemblage has major differences in behaviour and social organization, and subtle differences in appearance such as the dorsal (back) fin and saddle patche. Individual killer whales are commonly identified by patterns in the grey saddle patch located immediately behind the dorsal fin, and by natural markings (scars, nicks, etc.) on the dorsal fin itself.

Resident killer whales specialize in hunting salmon. They primarily hunt Chinook, but chum salmon are also eaten during the fall. The residents’ social organization is based on small mother-led (matrilineal) groups called matrilines, which can include three to fifteen individuals. Transients are marine mammal “specialists,” preying on harbour seals, sea lions, elephant seals, porpoises and baleen whales such as minke whales and gray whale calves. Unlike residents, transients may leave their mother’s group around the time they mature. Offshore killer whales are poorly known, but tend to travel in groups of 30 to 60 individuals, probably preying on large oceanic fish such as sharks and halibut.

Photos: Lance Barrett-Lennard

Some females give birth to their first calf at age 12, but most give birth at age 14-15. Usually single young are born; there is one documented case of twins in B.C. The length of pregnancy (gestation period) in aquarium killer whales has been recorded at close to 17 months and the maximum calving rate is one every three years. Females stop giving birth at approximately 40 years of age. Calves nurse from their mothers for at least one year, and sometimes up to 2 or 3 years.

Residents are only common on the coast from April to November, but some pods have been seen in inshore waters throughout the year. Some may go offshore or into mainland inlets during the winter. During the summer months, southern resident pods are commonly seen in Haro Strait and the San Juan Islands, and northern residents are often seen in the Johnstone Strait area.

Transients are found along the B.C. coast year-round, and are constantly on the move in search of their prey.  They are often found in areas where seals are abundant. A transient pod may range up to 1,500 km along the coast from Alaska to California; resident pods have been known to travel up to 2,200 km.

There are approximately 300 northern and southern residents and 225 transients in B.C./Washington waters. At least 200 offshore killer whales have also been identified. The South East Alaska resident population is just over 300 killer whales, and there are numerous other populations of transient killer whales in California and Alaska that are distinct from local populations.

Activities of both residents and transients can be grouped into four major categories: looking for food (foraging), resting, socializing and travelling. All of these seem to happen both day and night.Foraging is the most common activity, comprising about 60 percent of their daily activity. Resident pods in B.C. forage cooperatively and prey is often shared between individuals, particularly between mature females and juveniles. Mature males may sometimes hunt and eat independently from the rest of their group.

Members of transient pods cooperate to chase, corner and kill their prey, and share their kill with group members. When resting, pod members slow down, group together tightly, become mainly silent and dive synchronously for 4-5 minutes or longer. Resting episodes usually last two to three hours. Socializing also consists of sexual interactions and play among pod members. Beach rubbing is a traditional social behaviour among some northern resident pods.

Sticking their head out of the water (spyhopping) and aerial displays, such as breaching, tail slapping and dorsal-fin slapping, are most commonly seen during socializing episodes. These behaviours may represent play, but may also occur in other contexts such as foraging. Spyhopping seems to be a way of looking at the whales' surroundings; killer whales often spyhop when boats approach closely. Aerial behaviours are most likely displays of social excitement, dominance, or aggression. Transients may breach to startle or confuse prey, and tail-slap to stun or injure prey.

Resident killer whales are very vocal. They echolocate frequently and exchange calls and whistles to maintain contact with each other while traveling and foraging.. Resident pods have distinct dialects consisting of a set of 7 to 17 distinct stereotyped calls. All members of a pod will use all of these calls.. Calls do not seem to have specific meanings, such as nouns and verbs in human language, but may be used in different contexts.

In most pods, some calls are unique to the group and some calls are shared with other pods. Shared calls usually have pod-specific "accents." Pods with dialects that have a few calls in common are considered to belong to the same "clan." Pods within a clan have probably descended from a common ancestral group and are therefore more closely related to each other than to pods from other clans. Different clans often occur in the same area and pods from different clans may travel together. Pod-specific dialects probably convey information about pod relationship and are important in maintaining the cohesion and identity of the group. Slight changes to standard call formats communicate additional information such as the identity, location and emotional state of the vocalizing individual.