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Scientific Name: Orcinus orca
Suborder: Odontoceti
Family: Delphinidae
Size: 6 - 9,8 m
Weight: 6000 - 8000 Kg
Group Size: 3 - 25 individuals
Habitat: Inshore, Offshore
Hemisphere: Both
Orca (Orcinus orca)
Often misleadingly called Killer Whale, the Orca is one of the most fascinating, intelligent and socially developed creature inhabiting our planet. There are two good reasons not to use the name "Killer Whale":
  • Orcas are not killers (at least not as much as we are), in particular they do not kill or harm humans
  • Since Orca belongs to the "Delphinidae" family, scientifically speaking it is a dolphin, not a whale.
Orcinus orca is by far the largest member of the "Delphinidae" family.
It is a very powerful predator, and wherever it is found, it sits on the top of the food chain. This makes the Orca very vulnerable to human-made contaminants, because of the bioaccumulation of fat-soluble organic pollutants (such as PCB and DDT) in its blubber and organs.
Its distribution is so wide that Orcas can be seen (at least sporadically) in almost all waters of the globe. Even more interestingly, they have successfully adapted to any conditions, varying their diet based on local food sources.

Some of its characteristic features are:
  • Huge, powerful black body, with white eye patch, undersides and lower jaw
  • Tall, triangular dorsal fin (up to 180 cm in adult males), falcate in females (male juveniles can be mistaken for females)
  • Large paddle-like flippers (pectoral fins)
The Orca is a very playful and inquisitive Cetacean, that often spyhops and breaches.

It is a highly social mammal, that can live in larger or smaller groups depending mainly on its feeding habits in that particular area.
Indeed, despite of the existence of only one species (Orcinus orca), at least 3 different kinds of Orcas are known:
  • Resident
  • Transient
  • Offshore

- Resident Orcas

They are strictly fish eaters, and have been extensively studied in the waters off British Columbia, Alaska and Washington State. Their basic social unit is called matriline, which includes a female (the matriarch) and her offspring of both sexes.
A variable number of matrilines aggregate to form the next social structure, called pod.
All members of a pod share the same "dialect", which means they use a common set of vocalisations (in variable numbers, between 7 and 17).

Whilst matrilines remain the basic social structures for resident Orcas, and interactions between members of the same matriline are very strong, interactions between matrilines within the same pod are also known, and they definitely develop to a higher degree compared to those among members of different pods.
Talking about these interactions, one important exception has to be mentioned: mating occurs exclusively between members of different pods, and individuals belonging to the same pod never interbreed.
The different dialects may play a crucial role in allowing a particular Orca to choose its partners among those individuals who speak a different language.

Being fish eaters, Resident Orcas form large groups to maximise the efficiency of their catch. In British Columbia, where they mostly feed on salmon, they are very likely to be seen by Whale Watchers and Kayakers during the summer months (between June and October).
While hunting, Residents are highly coordinated and freely use echolocation (a natural sonar system) to both locate and stun their prey.

The Orcas of British Columbia were the first to be studied and indentified, by means of Photo ID techniques. The pioneer of this fundamental research was Dr Michael Bigg, whose work allowed to assess the real conservation state of the Orcas along with their feeding habits and social structure.
Mike Bigg found out that individual Orcas can be identified due to the different shapes of their dorsal fin, along with the presence of characteristic nicks and scars. Also, the shape of the saddle (the gray area right behind the dorsal fin) allow to tell individuals apart.
This technique has since become a standard around the world to identify Orcas.

The average day of an Orca was also shown to include 4 main activites:
  • Foraging
  • Resting
  • Socialising
  • Travelling
In British Columbia, where salmon is abundant during the summerly months and it is therefore a relatively easy prey to catch, Residents can spend a great deal of time socialising.
In Johnstone Strait (a place not to be missed by Whale Watchers!), Residents are known to spend some time every day at the Robson Bight (Michael Bigg's) Echological Reserve, in the world-famous waters of their Rubbing Beaches, where they rub themselves on pebble stones and display a wide variety of social interactions (perhaps including mating).

While the term "resident" was first intended for fish-feeding Orcas along the West Coast of North America, it is now broadly utilised to refer to any fish-eating populations, such as the one, for example, that inhabits the waters of Norwegian fjords in winter, which feeds on herring.

- Transient Orcas

Unlike Resident Orcas, Transients are strictly marine mammal eaters (though they sometimes feed on land mammals too).
First studied in British Columbia, Alaska and Washington, they have been found to prey predominantly on Harbour Seals, Sea lions, Harbour Porpoises, Dall's Porpoises. They are also known to attack and kill Minke and Gray whales (most attacks on Gray Whales are though recorded in Monterey Bay, California).

Transients have a different social structure to Residents. Groups are smaller, rarely exceeding 3 or 4 individuals, with a rather fluid structure, where some members often leave the group while new individuals join.
As an important consequence, all Transients in a particular area share the same language.

The specialised diet of Transients have striking implications on their behaviour: since they prey on "sound-aware" marine mammals (mainly Cetaceans and Pinnipeds), Transients stay almost silent while hunting, not to disclose their presence.
Communication among them is resumed only once they make a kill.

Also, they never spend too much time in a single area, and strongly prefer to move to the next feeding ground to gain surprise.

Because of the large amount of time spent travelling and hunting (up to 90% of day), very little is left for socialising and resting. It has been proved that Transient and Resident Orcas have been genetically separated for thousands of years. As a result, it is likely they will become eventually two different species.
In general, they ignore (if not avoid) each other.

- Offshore Orcas

More similar to Residents than Transients from a genetic point of view, little is known about Offshore Orcas.
They are believed to be fish eaters, based on the large number of individuals observed in offshore waters, which fits more a fish-hunting style of life.

Orcas around the world

As previously mentioned, Orcas appear to be a very versatile predator, and successfully specialised on one or more particular prey depending on local conditions.
For example, New Zealand Orcas feed primarily on Sting Rays, while in Crozet Islands they go mainly for Penguins, and Orcas off Gibraltar hunt Tuna in the summer months.


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