Marine Biology

Orca Killer Whales

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Even for those with little marine mammal knowledge the killer whale or orca (Orcinus orca) is immediately recognisable due to its distinctive black and white markings. Orca belong to the scientific order of Cetacea, a group which includes whales, dolphins and porpoise. The orca's sub-order is defined as Odontocedi or toothed whales, the family name is Delphinadae and the genus Orcinus.

The carnivorous orca is the largest member of the dolphin family and is found across a wide range of the earth's oceans and seas from polar to equatorial regions.

Populations number both resident and transient types and where the two occur in the same area they will not integrate but stay distinctly and seemingly deliberately apart.

Antarctic populations will range as far as the ice pack and even hunt its prey here while the Arctic populations do not approach the ice pack.

It is thought that among the populations of known orca, some may actually fall into sub-species categories or even distinctly separate species as yet unproven and in certain areas surprisingly little is known about orca particularly regarding migration patterns.

Orca are known to have an incredibly diverse carnivorous diet which often becomes specialised within certain pods. The diet can include fish, squid, sea-birds including penguins, seals, sea lions and more rarely walrus, dolphins, sharks and whales. It is known that orca can produce tonic shock in sharks – an ability which renders the shark immobile and helpless. Whales in certain areas have also been known to develop highly sophisticated and intricate co-operative forms of prey capture which include creating waves which wash over the ice-floes and flush seals into the waters and charging and beaching themselves on coastlines and rocks to capture sea lions. The latter is demonstrated in the now famous footage of the BBC's Trials Of Life series with David Attenborough.

Although the distinctive black and white markings are the most common for orca, variations have been observed, most notably in the Antarctic populations which may be pale grey and on rare occasions footage of pure white orca has been captured on film. The other main distinguishing feature of the orca is the huge dorsal fin which on males is pointedly triangular and may reach a height of two metres. Females have smaller curved dorsal fins which are about half the size of the male fin and their size and bulk in general are of much smaller proportions. Adult males may be up to eight metres in length and can weigh more than six tonnes while the female averages around six metres in length and weighs between three to four tonnes.

Very stable family groups, sometimes including members across four generations, which spend their entire lives within close proximity to each other, join with other groups to form pods which may number up to 40 individuals. These pods may disperse back to their family groups at times and remain apart for weeks and even months.

Orca use a series of sounds to communicate and each pod will have a distinct language to itself, known as a dialect, among marine biologists. These sounds are also believed to play a part in hunting. Orca also have a highly developed echo-location system which uses bounced sound transmission or echo to distinguish the shape, size and distance of other objects or creatures in the vicinity.

Adult female orca will produce one calf every 3 to 10 years after a 17 month gestation period producing on average five calves in a lifetime. All female members of a pod may play a part in the care of the young which have only a 50% survival chance at worst in the first few months of their lives.

Orca are long lived mammals when in their natural environment with females reaching a maximum of 90 years of age although usually around 50 years and males a maximum of 60 years of age.

The story is very different for captive orca which unfortunately, although improving, is still a significant issue for animal rights activists around the globe. Twenty-five years is the maximum life expectancy for a captive orca and the already depressing infant mortality rates are even higher than in the wild. Additionally, captive orcas have commonly displayed signs of stress and at times have been known to deliberately self-harm.

Orca are not widely considered to be a species under significant threat however the issues which affect all marine life such as oil spills, pollution, deep sea drilling, food source depletion and shipping activity may be cause for concern. Additionally, as marine biologists continue to work on the possible identification of distinct separate species among those orca all currently classified together there is the chance that some populations may be under severe threat and numbers dangerously low. This factor has led the IUCN to change the conservation status of orca from 'conservation dependant', a relatively low risk category, to 'data deficient'.

More about this author: Deneice Arthurton

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