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Killer Whales - Orcinus orca

Orcas, Sea wolves
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Orcas / Killer Whales Statistics

Maximum length: 9.8m (32.2ft) males / 8.5m (27.9ft) females
Adult weight: males: 11.1 tonnes max. / females 8.3 tonnes max.
Life span:
35-50 years
Sexual maturity: 12-16 years males / 6-10 years females
Gestation: 12-16 months
Birth length: 2 - 2.5m (6-9ft)
Birth weight: 180kg (300lbs)
Dive duration: 20 mins
Distribution: common in all oceans
Current world population:
up to 100,000, the majority (70,000) in Antarctica. Orcas weren't targeted by whalers, threats are interactions with fisheries and from pollution.




Orcas in Antarctica
photo Jean Cato / National Science Foundation
Killer whales or Orcas are probably the best known of the whales, as large carnivores they have a keen intelligence that enables them to be trained in captivity to do various tricks for rewards and so have been kept in marine aquariums and "Sea-World" type exhibits for many years. They are easily identified with their distinctive black and white patterning.

Killer whales are stocky in appearance compared to most whales which are quite long and slim relative to their length. Males are significantly larger than females (a trait known as "sexual dimorphism") and have a large and prominent dorsal fin (the one in the middle of their back) that can reach 6ft (1.8m) in height, the females dorsal fin is usually less than half this height.

They are Odontocetes or toothed whales and while they are quite small compared to the great baleen whales (Mysticetes) they are at the very top of the Antarctic food chain due partly to their formidable array of teeth, but most of all due to the fact that they often hunt in packs or "pods". Their tastes are wide ranging from krill, squid, fish and sharks to penguins, seals and even the much larger baleen whales.

Orcas are the largest of all carnivores on earth that feeds on a variety of foods, they are found in almost all oceans, from the tropics to the Arctic and Antarctic where they will go deep into the pack-ice to hunt seals and penguins. They are commonest in coastal waters and in cool temperate and sub polar seas.

They have very sharp stout conical shaped teeth, from 40-48 with equal numbers in each side of the upper and lower jaws. The teeth can be up to 5cm (2") long. When a pod of killer whales is feeding, they will co-ordinate their movements by a continual stream of clicks and calls. Ever ready to spot an opportunity, killer whales will even follow ice-breakers at the start of the season as they cut paths through the ice to reach deeper into the ice and perhaps get to seals and penguins that were beyond their reach.

So adventurous and opportunistic are killer whales in this respect, that groups of killer whales are thought to have spent an entire winter living in and around a polynia, an area of open water kept clear by currents and winds while surrounded by miles of closed ice. These killers were unable to return to the open ocean as they would have had to have held their breath under the continuous pack ice for longer than they were able.

In the days of commercial whaling, while Orcas weren't very much hunted themselves (they were much too small a catch to waste a harpoon on), they would often follow the whaling boats and rush at the dead baleen whales that were being flensed or towed alongside the boat ready for flensing and feed on the carcass. As such, they were much disliked by the whalers as they competed for the prey that they had just captured. Not for nothing are these whales called the "wolves of the sea".

Ecology and Behaviour


Killer whales swimming in McMurdo Sound Antarctica - Photo Donald LeRoi, NOAA Southwest Fisheries Science Center, National Science Foundation

An interesting aspect of the ecology of Orcas discovered from studies of populations off Washington state in the USA and up to Alaska is there are three distinct types that are very similar but differ somewhat in coloration in morphology (the way they look / proportions etc.) but most of all in their behaviour. These three types are known as "Residents", "Transients" and "Offshore", they are discrete populations and little or no mixing between them appears to take place.

Residents - These stay in one location all through their lives and form very stable communities. They tend to be mainly fish eaters which they are thought to catch with the help of echolocation. Their dorsal fins are more rounded at the top compared to the transients that have more pointed dorsal fins.

Transients - Move around more, they tend to feed on marine mammals, mainly seals. They form pods with less members than residents and are not so loyal to a particular pod.

Offshore - The least of all is known about these (as they live mainly offshore) but they form large pods and move following the edge of the continental shelves.

Though these groups have only been studied to any depth in the North Western United States, indications are that the behavioural types exist elsewhere too.

Orcas feed on a huge range of prey. More or less, if they find it and catch it, they'll at least have a go at eating it. Different pods of Orcas seem to have different specialties  of diet and will specialize in a particular type of prey developing and becoming skilled in the ways to capture that prey. For instance they have been seen:

  • Co-operatively herding fish such as herring together into tight groups and then slapping them with their tails to stun them. Otherwise a herring would be a lot of effort and a small mouth-full for such a large animal.

  • Surprising young and unwary sea lions off the coast of Patagonia by chasing after them right into the shallows and then lunging with a great snap of their powerful jaws. Returning to sea after a near stranding in these cases takes quite an effort for the whale.

  • Attacking the great baleen whales such as blue whale by tearing at and eating the great tongue. A pod of 40 or so Orcas have been seen engaging in this behaviour attacking a solitary huge adult blue off the coast of California.

  • Breaking through sea ice from below to surprise seals and penguins, or seeing them on ice-floes and then pushing upwards on the floe to tip the prey into the water. Alternatively two whales may rush at an ice floe which is then washed over by a large wave which dislodge the seal or penguin.

 

Killer whales are often approachable by boats and are generally inquisitive. They are frequently active at the surface showing such behaviours as lobtailing, flipper-slapping, spyhopping, wave riding and breaching.

Rubbing against a hard surface such as rocks or even other whales is often seen. It is thought to serve as a comfort movement and helps to remove dead skin. Certain rock rubbing areas may be socially important.

Like all whales, sound is very important to killer whales. Researchers have even identified unique sounds and discrete calls that are distinctive to certain pods and family groups, to the extent that killer whale dialects can be identified.


Orcas or killer whales in Alaska - picture courtesy Christopher Michael - Creative Commons Attribution 2.0 Generic licence

Killer Whales
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Killer Whale Swimming Past a Tabular Iceberg
Killer Whale Swimming Past a Tabular Iceberg
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