About killer whales

The killer whale is the largest member of the dolphin family. The species has adapted to living in a variety of environments from tropical to polar seas and preys upon a wide range of species, varying from schooling fish to large whales. However, most killer whale populations do not behave as generalists but specialize on certain types of prey. The prey choice is of central importance to the behaviour, habitat use and distribution pattern of the different killer whale populations. In Norwegian waters the Norwegian spring-spawning herring is the main type of prey for killer whales. Killer whales occurring in the coastal waters of Iceland feed also on (Icelandic summer-spawning) herring and there are several similarities in the behaviour of Icelandic and Norwegian killer whales.

Killer whales are sexually dimorphic, meaning that it is possible to distinguish between mature males and females based on their appearance. The largest killer whale male which has been measured was 9.6 meters long, the longest female 8.2 meters long. The average length of Norwegian killer whale males is 7 meters, of females 5.5 meters. In addition to their larger body size, adult males have a taller dorsal fin than females.

In addition to the fact that it is possible to distinguish between adult males and females, it is also relatively easy to identify killer whale individuals. Photographs taken of the dorsal fin and the grey saddle patch behind the fin can be used in identifying individuals, since the pigmentation, shape and scar pattern on these areas are unique for each whale. This technique, called photo-identification, has revealed several fascinating details about the number, distribution and social organisation of different killer whale populations.

Common to all killer whales is that they live in groups; single killer whales are rarely sighted. Again, the group size and stability varies among the populations. The most common social organisation among killer whales consists of matrilineal, stable family groups. In practice this means that killer whales of both sexes stay in the group they were born into throughout their lives! So the large adult males in a group are not the fathers of the calves, but rather their uncles or big brothers. Another remarkable aspect of these stable matriarchal groups is that each family has its own vocal dialect. Long term photo-identification studies of killer whales in Norway have shown that here the killer whales also live in stable family groups.

Mating most commonly occurs between groups, but within a population. Killer whale gestation period is estimated to be 16 months. The Norwegian killer whales have a peak in calving in late fall (November-December) and therefore mating season should be in late summer. Killer whale females get sexually mature at about 13-15 years old and they get one calf every 3-5 years. The females stop breeding when they are about 40 years old but continue to live several years, even decades after their last calf has been born. The old matriarchs may have an important function in the groups where much of the behaviour is learned.