Killer whales are instantly recognisable, their black and white colouring setting them apart from other cetaceans. The killer whale, or Orca, is in fact the largest species of dolphin, and like other dolphins is both intelligent and trainable. They are, however, ferocious predators, as the recent incident at the SeaWorld park in Orlando, Florida, sadly demonstrated. Highly sociable, the killer whale hunts in groups known as pods, and are the top predators in the sea. Although young calves, or elderly and sick whales may be attacked by sharks, a healthy, adult killer whale has no natural predator.
A fully grown killer whale can reach up to 32ft in length, and weight in at 6 tons. They will eat virtually anything, including fish, squid, seals, sea lions and even other species of dolphins and whales. They have been known to pluck seals off the ice, and to grab birds in flight, with the help of their 4 inch long teeth. They have also been seen to play with their prey, tossing the still live bodies of seals around, before finally eating them. They have different strategies for hunting particular prey, each member of a pod having a specific role to play in the hunt. For this reason they are often likened to wolf packs.
Killer whales are found in all the oceans of the world, but prefer colder, coastal waters. As to their social structure, three main behaviours have been observed, and the whales that display them have been given the names ‘resident’, ‘transient’ and ‘offshore’. Resident killer whales usually occupy coastal waters, live in family pods, and mainly hunt for fish. The pods can contain up to 40 members, with both female and male whales, young and old living together. They are all related through the female line, and as whales can live between 50 to 80 years, there may be four generations swimming together. Females are sexually mature at the age of 15, and usually produce a single calf every five years or so, after a 17 month gestation period. The sexually immature females in the pod will help with looking after and protecting calves. Killer whales use echo-location to hunt, and also for communication between pod members, and each distinct pod will have its own ‘call-signs’. Social interaction is varied and complex, and the whales are in almost constant communication.
Transient killer whales travel in groups of between 2 and 6, and hunt for marine mammals. The social bonding is not so great and the animals communicate less frequently. Transient killer whales hunt over far greater distances than resident killer whales. Both groups may live in the same waters, but will not interact. The fact that each group is hunting a different prey, means that they will not come into conflict. It seems that resident and transient groups are not genetically related in any way, and that eventually they will diverge into different species.
The third group of killer whales, the offshore, are, as the name suggests, found in the open ocean. Much less studied than the other two groups, they were first observed in the Northeast Pacific. These whales are found in groups that range from 20 to 70 individuals, and they primarily hunt large schools of fish. Occasionally, much greater numbers are observed, hundreds of killer whales congregating together. Research is still ongoing to explain this behaviour, and how the whales are related.
Although the killer whale has never been commercially hunted by man, their populations are under threat, both by climate change and deaths due to pollution. Especially for the resident killer whales, the over-fishing of their prey fish by man is also effecting numbers. It would be a sad day indeed, if these magnificent animals were to vanish from our oceans.
this article was written with reference to the following sources,
http://animals.nationalgeographic.com/animals/mammals/killer-whale.html
http://news.bbc.co.uk/1/hi/8535618.stm
http://www.vanaqua.org/education/aquafacts/killerwhales.html
