Orca (Killer Whale)
Orcas are distinctive in appearance with large black bodies, a white underside, a white patch above and behind the eye, and a grey 'saddle patch' behind the dorsal fin
At up to nearly 10 metres long, males are larger than females and have a tall dorsal fin - up to nearly 2 metres in height. The tall sword-shaped and strikingly visible dorsal fin makes them almost unmistakable at sea. Female length is about 20% less and the curved dorsal fin is less than half the height of the males.
Orcas are the apex predators of the sea and the largest members of the dolphin family. They are highly intelligent, highly adaptable and able to communicate and coordinate hunting tactics. Not typically a migratory species, orca ‘migrations' are principally in response to changes in favoured prey abundance and can sometimes be long, e.g between Alaska and California. Depending on the type of social group and location, orcas will hunt fish, squid, seals, sea lions, seabirds and even whales much larger than themselves. There has never been a documented attack on a human in the wild, and there are some stories of orcas actually protecting humans at sea from sharks. The taxonomy of this genus however is clearly in need of review, and it is likely that Orcinus orca will be split into a number of different species or at least subspecies over the next few years.
Orcas are extremely fast swimmers and have been recorded at speeds of up to 54km/h. Most studies have centred around the Pacific Northwest where three distinct ecotypes exist: coastal fish-eaters (‘residents'); marine mammal eaters (‘transients') and ‘offshores' – whose dietary habits are unknown. One striking feature of the ‘resident' orcas in this area is that no apparent dispersal or immigration of birth group has been recorded in 30 years of study, making them one big family group.
A ten-year study in Kamchatka has identified two separate ecotypes of fish-eaters and transients. In Antarctica three ecotypes are recognised with more pronounced morphological and biological differences. Various specialised hunting techniques have been observed. Off Peninsula Valdes, Argentina, and the Crozet Islands, orcas feed on South American sea lions and Southern elephant seals in shallow water, even beaching themselves temporarily. Adult killer whales have been observed to teach the younger ones the skills of hunting in shallow water. Another technique for capturing seals is known as wave-hunting: killer whales spy-hop to locate seals resting on ice floes and then create waves by swimming together in groups. As the water washes over the floe, it makes the seal slide into the water where an orca waits to kill it.
Orcas are found throughout the world's seas, typically in extended pods, or family groups, that share a common dialect. Relationships with other pods can be deduced by determining the number of calls they share indicating degree of relatedness. Pods that share no calls are in different clans or communities. Though cosmopolitan in distribution they are most abundant in cold, temperate, coastal areas. In general, orca populations have probably been affected by human activities to relatively small degree when compared with other marine mammal species. However, habitat degradation, prey depletion and pollution now threaten certain populations.
Orcas also continue to be an attraction at marine parks; orca populations in the US and Canadian Pacific Northwest, Iceland and Japan were negatively impacted from the 1960s to the 1980s by the live capture industry. The ‘southern resident' orcas of the American Pacific Northwest were particularly affected and this, together with other environmental factors, has resulted in this declining population being classified as ‘Endangered'. Although the IUCN classifies the species as Data Deficient worldwide, a regularly encountered population of only 32 individuals in the Strait of Gibraltar, each one known and identified by researchers, is listed as Critically Endangered (IUCN).