The hunting methods of the orca



by LORENZO CIOTTI

The hunting methods of the orca

The orca normally lives in groups consisting of the female. This is a matrilineal base family also called a pod. All members of this family communicate with each other through sounds of various kinds and each pod has its own language.

The orca has a specific organ on its forehead that it can use as sonar. All objects hit by sound waves send back an echo that orcas perceive as an animal or rock to be avoided. Killer whales are highly social animals and hunting involves the whole group.

The type of prey depends on the habits of the group: populations called residents are sedentary and essentially feed on fish. Transients, on the other hand, mainly hunt marine mammals such as seals, sea lions and even whales.

Penguins and other seabirds are also part of their diet. In 1988, a new type of population called offshore was discovered in the open sea, which travels in groups of about 60 specimens but which can reach 200, genetically distinct from transients and residents.

It is little known, although the Offshore females are recognized because they have stripes surrounding the fins. Some populations have developed peculiar hunting techniques. For example, the Argentine killer whales gather in February in front of the beaches where sea lions reproduce to hunt the still inexperienced pups.

The technique is simple: an individual swims in front of the beach with the dorsal fin clearly visible above the surface of the sea thus making itself noticed, another individual, keeping underwater, crosses from the opposite direction.

If there are careless pups resting on the shoreline, the hidden killer whale swims towards the beach with impressive speed trying to capture its prey. In this enterprise the animal runs ashore, but with decisive movements of the body it slides back regaining the sea and carrying any prey with it.

Antarctic killer whales, on the other hand, use waves to make seals slide off the ice: the matriarch goes to the opposite side of the iceberg to spot the seal and then warns the others with a signal. Then the rest of the pod swims at high speed to the iceberg causing a big wave and causing the seal to slip.

New Zealand killer whales instead use a peculiar technique to capture stingrays, they lie belly up catching the stingray and then roll over causing the stingray to fall into a state of tonic immobility. During their sea voyages, orcas often come into contact with other large predators of the sea.

Encounters with mako, tiger and white sharks have been documented. On October 8, 1997, near the Farallon Islands, the clash between an orca of about 6 meters and a white shark just over half as long was filmed. In late 2009, marine biologist Ingrid Visser and her team documented the predatory behavior of orca pods off the coast of New Zealand with several photos of large mako and great white sharks.

A couple of killer whales in South Africa was also observed while they hunted numerous white sharks and their hunting system was seen: with strokes of their tail they stun the shark which first tries to escape, then one of the killer whales, dividing the tasks, passes under the belly of the shark by biting it and tearing off the part that corresponds to the liver, an organ that killer whales are greedy of as it is rich in nutrients, especially squalene.

The orca also attacks and kills the walrus. The only animal capable of overpowering her is an adult sperm whale which, thanks to its diving ability, manages to escape her. Specimens not yet mature can instead be included in the diet of the killer whale itself.