Orca  (Orcinus orca)

The orca, once also known as the killer whale, is in fact the largest of the dolphins (1). They are easily identified by the black and white colouration; the underside is white and there are white patches behind the eyes, and a greyish white area called a 'saddle-patch' behind the dorsal fin (1). The shape of the saddle is unique in each animal, and can help to identify individuals (4). The dorsal fin is also used to recognise individuals (4). Male orcas have the tallest dorsal fin known in the animal kingdom (4), measuring up to 6 feet high in mature males (1), it can be as tall as a man (4). Females have shorter, more curved dorsal fins (4).

Found in every ocean, the orca is one of the most widely distributed animals known (1). In the UK, it occurs most often around northern and western Scotland, and closer to shore between May and October (3).

Inhabits both coastal and offshore waters (5). They have also been known to venture into estuaries (5).

Orcas are the top predator in the sea and have an extremely broad diet, including fish, gulls, penguins, turtles, squid and marine mammals, even including large whales such as grey and blue whales (1). They spend their life in stable groups, called pods (1), which hunt co-operatively (6). Long-term studies off Canada have shown that orcas occur as 'transient', 'resident' or 'offshore' populations, which have different hunting styles and social organisation (4). Orcas are extremely active and acrobatic; they are one of the fastest animals in the sea and often breach (clear the water), lobtail (slap the tail flukes on the surface of the water), and spy-hop (bring the head out of the water) (4). Females become sexually mature in their teens and produce a single calf every three years until they reach around 40 years of age (6). After the gestation period of up to 17 months, calves are suckled for about a year (6). Killer whales live to between 50 and 100 years of age (6).

The orca is threatened by hunting, prey depletion, and exposure to human activities such as disturbance from boats including whale-watching crafts, particularly when they venture closer to shore (3). As it is the top predator it is particularly vulnerable to contaminants, which build up in the tissues of prey species and subsequently affect the predator (6). Furthermore, the captivity industry has posed a threat, taking live individuals for the aquarium trade (1).

The orca is a UK Biodiversity Action Plan priority species (3). It is protected in UK waters by the Wildlife and Countryside Act 1981 and the Wildlife (Northern Ireland) Orders 1985; it is illegal to intentionally kill, injure, or harass any cetacean (whale or dolphin) species in UK waters (3). The Agreement on the Conservation of Small Cetaceans in the Baltic and North Seas (ASCOBANS), has been signed by 7 European Countries, this includes the UK. Provision is made under this agreement to set up protected areas, promote research and monitoring, pollution control and increase public awareness (3).

For more on this species see the WDCS species guide, available on-line at:
http://www.wdcs.org/dan/publishing.nsf/allweb/5A29EEE0457F51E9802568F8004F3829 For more on whales and dolphins and their conservation see the WDCS homepage:
http://www.wdcs.org/

Information authenticated by WDCS, the Whale and Dolphin Conservation Society:
http://www.wdcs.org