Killer whales (Orcinus orca) are the largest and oldest species of the dolphin family, which consists of almost thirty-five species. As this family is closely related to that of whales, some of the species of dolphins, including killer whales, are referred to as whales. Killer whales are found in the oceans across the globe, including the polar regions. Five types have been recognized till date, with more research in the offing.
Killer whales are characterized by black backs, white chests, and white-colored patches above and behind the eyes. In case of the Antarctic killer whales, their backs are light gray to white in color. A killer whale has a large dorsal fin, with a dark gray saddle patch on its rear. The pectoral fin of a male killer whale is twice the size of the female's and is more triangular in shape. Compared to other dolphin species, the pectoral fins of killer whales are more rounded and large and are noticeably bigger in size in the males. These aquatic mammals can grow up to eight meters in length and six to ten tons in weight.They are considered as one of the fastest marine mammals, capable of moving at speeds of up to 56 km/h. All the features can be more prominently seen in males, as compared to females and the young.
Killer Whale Types
The main factors which are taken into account while classifying the killer whales are its geographical distribution, physical appearance, and the type of prey they feed on. As per these factors, there are around five types. Earlier, three types were recognized during the 1970s, but later three more from the Antarctic were added to the list. According to the earlier classification, killer whales are of three types - resident, transient and offshore. The first category, resident ones are the most commonly seen among the three types in the coastal waters of the northeast Pacific. They are seen in groups, mainly matrilineal ones. The second category, known as transient killer whales, are usually seen in small groups with two to six members, and are more attached to each other. Unlike the residents, the female transients have more triangular and pointed dorsal fins. They are commonly seen along the coasts, as they travel extensively. The third category is called offshore killer whales and are found in open waters. They move around in large groups, comprising almost 60 members. This type is differentiated from others by their short stature. The females have a more rounder dorsal fin.
Those found in the Antarctic are categorized as type A, type B and type C. Type A consists of killer whales with a large black and white body and an average-sized eye patch. Type B killer whales are comparatively smaller and possess a gray-colored patch on their back apart from a large white eye patch. Type C comprises the smallest members, with their eye patches slanting downwards.
What do Killer Whales Eat?
As the food they eat is also considered a factor in classifying killer whales, let us look at the eating habits of these aquatic mammals according to their various types. Resident types feed mainly on fish and squids, whereas the transients' diet consists of marine mammals and not fish. The offshore killer whales feed on schooling fish. Type A of the Antarctic variety eat minke whales, while type B feeds on seals.
They adopt a technique called herding to catch their prey. The members of the group surround a group of fish or other prey and restrain their movement by confining them to a small area. Then individual members of the killer whale group feed on the prey. In case of larger preys, killer whales use their tail fluke to kill the prey and then with the help of their sharp teeth, they tear apart the prey before swallowing it. It is also been observed that these killer whales drink sea water and their kidneys can remove the salt form the water. They can adapt easily to any place, as they move from one place to another more often. They are also known at times to change their eating habits.
Types of Prey
Even though research is ongoing regarding the feeding ecology of killer whales, they are known as the 'wolves of the sea' for their hunting habits. An average killer whale needs around 230 kilograms of food every day. Their food includes fish, aquatic mammals and birds. Around 30 species of fish are consumed by the killer whales who feed on fish. This includes salmon, chinook, coho, herring, tuna, whale sharks, smooth hammerheads and basking sharks. There are instances of these marine mammals feeding on great white sharks, stingrays, and octopuses. They also eat squids, sea turtles, and some reptiles.
It has also been observed that the diet of killer whales includes 22 species of dolphins, whales and porpoises. Usually weak and juvenile whales are attacked by killer whales, who avoid sperm whales, which are bigger in size. They also feed on marine mammals like sea lions, seals, fur seals, walruses and sea otters. They are also found to attack terrestrial mammals swimming between islands. Another food item of killer whales are birds, which include penguins and sea gulls. While there are cases of captive killer whales attacking humans, there are no such reported cases regarding the wild ones.
Even though the diet of killer whale consists of a wide range of prey, different types feed on different prey. As stated earlier, residents eat only fish and transients feed on marine mammals. It is implied that those in the polar regions have the chance to feed on penguins. Thus, the diet of killer whales depends on the region and type of this aquatic mammal, which is at the top level of the food chain.