Size: Males = 6 - 10 m (20 - 33 ft.) and Females = 5 - 8.5 m (16 - 28 ft.). Size varies geographically with larger animals in the Southern Hemisphere
Weight: Males = up to 10 tonnes and Females = up to 7.5 tonnes
Diet: Extremely diverse and can range from small schooling fish such as capelin up to large baleen whales
Killer whales (Orcinus orca), or orcas, are toothed whales belonging to the dolphin family. They are the largest dolphin species, reaching lengths of up to 10 m (33 ft.) and weights of up to 10 tonnes. The black and white colouring, robust body and tall dorsal fin give the whales a somewhat chilling yet majestic and beautiful appearance. They are often called the “wolfs of the sea” due to their often cruel hunting methods. They are most definitely at the top of the food chain. Killer whales hunt in packs and are highly organised. Younger animals in the group are taught specialised hunting tactics by the older animals. During training, the young animals are allowed to practice with the half-unconscious prey, which makes it seem as though the whales are playing with the prey for no reason. The real reason involves training. Killer whales are unbelievably willing to learn, have developed quite complex communication system and also form lifelong, deep ties within the group.
Killer whales usually stay in smaller family groups of 2–9 individuals of both sexes and all age groups. The groups are usually related along matrilineal lines, in which case the oldest female is the ultimate ancestor of the others in the group. There is considerable unity within the group, and the ties usually last throughout their life. Their strength, however, does vary according to stock and variant as well as group composition. There are 9 different variants of killer whales that have been defined in the world. Sexually mature males seek out unrelated females from other groups to mate with and then return to their own family and usually take no part in raising their offspring. The family groups often remain in close proximity to other closely related family groups, or the extended family, as maintaining good relations with close relatives increases successful hunting and care of calves. Thus, good relations and trust are extremely important and are only possible due to developed social communications.
The average swimming speed of killer whales is around 5–6 kph (3-4 mph), and they generally do not swim faster than 10 kph (6 mph). The can, however, swim up to 40 kph (25 mph) in short bursts of speed. Killer whales usually feed near the surface but can dive to a depth of around 100 m (328 ft.).
Mating usually occurs where large family groups congregate in large herds. There is a lot of excitement at such times, and a great deal of sexual behaviour goes on. Mating can occur at any time of the year. The females become sexually mature at 10–15 years and are fertile to the age of 40. They live for a long time after their fertile period ends, as the group benefits from their experience and knowledge of the sea’s mysteries. The males become sexually mature at aged 16. The females calve approximately every 3–8 years, although this can vary tremendously depending on the condition of the stocks. The calves suckle for around 15–18 months.
Killer whales use a range of whistles and calls for communication and, as other toothed whales, they use echolocation pulses to find their way around and to find prey where visibility is poor or lighting is low. Numerous dialects have been found within the killer whale sound system, and different dialects can also be found between ocean areas and even within extended families. Family groups often have their own distinctive sound calls which are characteristic to the group. This makes it easier for the whales to identify each other and find their way back to the family after having separated for a while. Such highly developed sound communications are considered unique in the animal kingdom.
Habitat and distribution
Killer whales can be found in any ocean, right from equatorial areas to the edge of the icepack in both polar regions. They have the most extensive distribution among all mammals. They can be found in coastal areas as well as out on the ocean. Migration patterns have not been established among killer whales, although there is some difference in the location of each stock according to season. Their concentration is much greater in colder seas, which is believed to be the main reason many baleen whales prefer to calve in warmer seas where the concentration of killer whales is less. Killer whales have been observed in the waters off the Icelandic coast in most months of the year and are extremely common on herring fishing grounds.
Life expectancy and population size
The maximum age of the females is considerably higher than that of males given that highly experienced matriarchs are of great importance to the group. They know the best feeding grounds and know the best hunting techniques. Females can live 80–90 years, while males reach a maximum of 50–60 years. The average life span of males, however, is only around 30 years. The population around Iceland is believed to be around 5,500 animals, while population between Norway, Iceland and the Faeroe Island is believed to be 13,000 animals.
As killer whales are at the top of the food chain, they have no natural enemies. However, since they are apex predators there is more bioaccumulation of various persistent toxins in their tissues than in other marine mammals. The effects of these toxins on killer whales are not well known, although it is has been shown that these materials have a negative impact on the immune system and fertility of mammals. Killer whales inhabiting Arctic and sub-Arctic waters have higher levels of accumulated persistent pollutants in their tissues than polar bears, but the effects of these substances are beginning to have a considerably negative impact on polar bear fertility.