Orcas: History and Hotspots
By hunting in packs, these marine mammals have earned the title of ‘whale killers’
Wolves of the Sea
Orca (Orcinus orca) is the largest member of the oceanic dolphin family. They have been known by many names. Ancient mariners saw them preying on large whales and called them ‘whale killers’. In modern times, this title has been modified to ‘killer whales’ in reference to their bulk and size. Their habit of hunting in coordinated packs has earned them the fearsome title ‘wolves of the sea’.
Marine Pandas
The Latin ‘orca’ literally means shaped like a barrel or cask. This is an apt description of the animal’s body, which is cylindrical and tapers at each end to form a hydrodynamic shape. The snout is blunt and they have powerful jaws, with teeth up to 10cm long that mesh when the mouth is closed. Adult males typically range between 6-8m in length and weigh in excess of 6 tonnes; the largest orca ever recorded was 9.8m long and weighed 10 tonnes. Females are smaller, generally ranging from 5 to 7m and 3-4 tonnes in weight.
Orcas have a highly distinctive black-and-white patterned body, with shiny black backs, white chests and patches of white above and behind their eyes. As a species, they are among the world’s most easily recognized marine mammals. Individuals can often be identified by subtle variations in their saddle patch and dorsal fin. The paddle-shaped pectoral fins are large and rounded. The dorsal fins of males are a tall (up to 2m), elongated triangle, while those of female's are shorter and more curved.
Their shape, size and strength make Orcas extremely powerful swimmers. They have been recorded at speeds of up to 30 knots (54kph) and a wild orca pod can cover over 160km a day. One study tracked a group of orcas from the waters off Alaska to those near central California, a distance of more than 1,900km.
Range and distribution
Orcas live in every ocean and sea, except the Baltic and Black Seas, making them the most widely distributed mammal on the planet, other than humans. They frequent the open ocean but mainly inhabit coastal and continental shelf waters less than 1200m deep. Although orcas roam temperate and tropical areas, they clearly prefer higher latitudes and are more densely concentrated in the cold waters of the Arctic and Antarctic where their large prey species are more abundant.
Around Australia, orcas have been sporadically sighted in all state and Northern Territory waters, with regular concentrations occurring off Western Australia. A ‘hot spot’ off Bremer Bay is believed to be the largest aggregation in the Southern Hemisphere, with an estimated population of between 50-100 inhabiting the continental shelf just 20nm (37km) offshore. Little is known about orcas on Australia's east coast. Amateur whale watchers have reported sightings from Hervey Bay to Hobart and along the Victorian coast as far west as Portland. While they have catalogued about 60 individuals, researchers believe the numbers are in the low hundreds.
Orca society
Orcas are extremely social animals and live in tightly bonded families that form part of complex societies. The family unit is a matrilineal group led by the eldest female with her sons, daughters and the daughters’ offspring. Multiple families may form loose aggregations called ‘pods’, comprising between 30-50 individuals. All members of a pod work cooperatively raising young, taking care of the sick or injured members and hunting. DNA testing indicates that males nearly always mate with females from other pods to avoid inbreeding.
Females are smaller than males with shorter dorsal fins
Male orcas have tall triangular dorsal fins
Intelligence, behaviour and language
Orcas are highly intelligent animals and exhibit curiosity, playfulness and an ability to solve problems in their daily activities. Adult orcas teach skills and pass on knowledge to younger individuals, such as what to eat, where to find it and how to catch it. For their part, the youngsters show a remarkable aptitude for learning and imitation. They frequently engage in surface behaviour such as breaching, spy-hopping and tail-slapping.
Orcas have good eyesight above and below the water, excellent hearing and exceptionally sophisticated echolocation abilities which are fundamental to orientation, feeding, and communication. They produce three main kinds of sound (vocalisations): clicks, whistles, and pulsed calls. By emitting clicks and listening for echoes, orcas are able to determine the size, distance, shape and direction of prey and other objects in the water. Whistles are continuous and used for social interactions and play an important role in close-range acoustic communications. Pulsed calls are used to communicate with one another. All members of a pod use a complex repertoire of calls, known collectively as a dialect, which is unique to the pod and passed on from one generation to the next.
The apex predator
Orcas are apex predators, with no natural competitors except possibly other killer whales and humans. Wild orcas are not considered a threat to humans, but captive orcas have made nearly two dozen attacks on their handlers, some of which have been fatal.
An adult orca consumes an average of 220kg of food each day, while fully weaned calves can eat up to 10% of their body weight during growth periods. Their diet may include fish, squid, turtles, penguins, polar bears and other marine mammals such as seals, sea lions and whales. They are the only animal known to predate on great white sharks. The orcas of Bremer Bay feed predominantly on squid, beaked whales and tuna, but also target large baleen species such as Blue Whales, Humpbacks and Antarctic Minke Whales.
Orcas forage cooperatively in pods and have developed sophisticated hunting methods to catch their preferred prey. They will use their numbers to herd schools of fish into a concentrated ball before attacking. Antarctic species swim closely in line abreast to create a strong bow wave that can wash a seal from an ice floe. Other seal eaters have perfected the technique of beaching themselves to grab their prey before wriggling back into the water.
Whale killers
Marine biologists conducting research in the Bremer Bay area since 2014 have documented several instances of orca packs successfully attacking and killing large whales, including three blue whales in the past three years. On each occasion, the attacks have involved up to 50 orcas operating in coordinated groups of 6 to 8 individuals led by an adult female. Their tactics have varied depending on the size of the whale and whether it was accompanied by a calf. When hunting a large adult whale, orca pods have attacked from several angles, taking turns to harass it by biting fins and flinging themselves over the blowhole to suffocate it. Female whales with calves have been chased for hours to the point of exhaustion, when the pair was separated and the calf drowned by preventing it from surfacing.
Old Tom
Shore-based whalers operating out of Eden (NSW) in the early 20th century were often assisted in their hunting by a legendary orca named ‘Old Tom’.
Tom and his pack would ambush migrating whales off the coast and drive them into Twofold Bay and the harpoons of the waiting whalers. On other occasions, Tom would swim to the whaling station at Kiah Inlet and splash about to attract the whalers’ attention, then lead the boats to where a whale had been rounded up by the pack. Tom often seized a boat’s harpoon line to slow a whale down for the kill, and over the years his teeth on the left side became worn down to the gums. When the killing was over, the carcass would be anchored and buoyed, then temporarily left to the killer whales which would feast only on the lips and tongue. After their ‘reward’, the orcas would cruise out to sea in search of more victims for their whalemen ‘partners’.
In September 1930, Tom’s body was found floating in the southern part of the bay. His skeleton was preserved and is now on display at the Eden Killer Whale Museum. Post-mortem analysis puts Old Tom’s age at about 35 years. After Tom’s death, the orcas moved away and Eden whaling, already in decline through scarcity of whales, came to an end.