Killer whales (Orcinus orca) – General information
Killer whales, also referred to as Orca’s, from a shortened version of their scientific name Orcinus orca, are one of the world’s most well recognised cetaceans. This is largely due to the exposure they received from the ‘Free Willy’ films and the demand for them in captivity for performances. Unfortunately, none of these situations portray the world’s largest dolphin as the impressive top predator that it is. Throughout their worldwide distribution, several communities of killer whales occur, separated by their prey preferences, with some eating only marine mammals, others only fish and some a combination of both.
In general, killer whales are black dorsally (on top) and white ventrally (underside). They have distinctive white eye patches and a grey saddle behind the dorsal fin. . Males reach average lengths of approximately 9m and can weigh over 9 tons (9000 kg). Female are smaller averaging 7 m in length and up to 4 tons (4000kg). Adult male killer whales are easy to recognize by their extraordinarily large dorsal fins, some reaching nearly 2 m high. Juvenile males and females have much smaller dorsal fins that are about 90cm high.
Males reach sexual maturity at around 15 years of age and females around 9 years of age. The breed every 3-8 years and have a 15-18 month gestation period. They generally give birth in autumn to spring but can calve all year round and the calf is nursed for 1-2 years. Females have a longer average lifespan of 80 -90 years, whereas males average 50 -60 years. The older Orca known is “granny” that is estimated to be 103 years and still lives with her pod.
Killer whales exhibit a wide range of feeding behaviours and have a large list of prey species ranging from large whales and porpoises, seals, dugongs and sea otters to numerous fish species and even birds, turtles and cephalopods. As one of the fastest swimming dolphins (50km/hour) making them capable of unpredictable turns and cooperative hunting, very little can escape these impressive predators.
Orcas have developed different hunting techniques depending on where they live and what they eat. In Norway, the Orcas herd fish into tight balls and then slap their tails into the ball to stun the fish making them easier to catch and feed on. In Argentina, Orca’s appear to strand themselves in an attempt to catch seals on the beach. They then wiggle themselves back into the ocean. One of the most amazing hunting stories’ for Orcas comes from Eden in Australia when a pod of orcas worked alongside whalers for 90 years (1840-1930) to catch Humpback whales. The orcas would chase the whales into Eden Bay and call on the whalers (by slapping their tails) to come and help them with the kill. Then whalers would come and harpoon the whale and leave it overnight for the orcas to eat the tongue and jaw.
Orca’s have also been reported to be curious towards boats and kayaks, often spy-hopping nearby. As exciting as this is for the human spectators, this behaviour is reflective of that used to search for prey on ice floes and rocky outcrops. Some impressive footage of orcas searching for seals on ice floes has recently been captured. The orcas spyhop next to the floe and then co-operatively swim towards it and under it at high speed, creating a bow wave that knocks the seal off into the water from where it is consumed.
Orcas are arguably the world’s most widely distributed cetacean species and occur in coastal and oceanic waters migrate according to their food. They seem to prefer colder coastal waters where food abundance is high. At least 4 ‘Types’ of killer whale have been described and scientists are working on the genetic and ecological differences between these types. Current thinking is that each type represents a completely isolated genetic stock. Globally, killer whales are classified as ‘data deficient’ by the IUCN, pending further studies on their abundance, distribution and threats. Read up on South African Killer whales in the next article.
– Culik B.M and Wurtz M.2010 Review of Small Cetaceans. Distribution, Behaviour, Migration and Threats. 2004 Marine Mammal Action Plan / Regional Seas Reports and Studies no. 177 2002–2010 Conservation Action Plan for the World’s Cetaceans
– Pitman RL. Ensor P. 2003 Three forms of killer whales (Orcinus orca) in Antarctic waters J. CETACEAN RES. MANAGE. 5(2):131–139, 2003
– Reeves RR. Smith BD. 2003 Dolphins, Whales and Porpoises IUCN/SSC Cetacean Specialist Group IUCN – The World Conservation Union
Best, PB. 2007. Whales and Dolphins of the Southern African Subregion. Cambridge University Press.