Aquarium of the Pacific - Online Learning Center - Species Print Sheet
Killer whales, or orcas, are the largest of the dolphins. Like other odontocetes or toothed whales, they have one blowhole and are able to use echolocation, which is similar to SONAR, to navigate and locate prey. There are three specialized sub-populations of these whales that differ genetically, physically, in foraging behaviors, diet, and in social organization—residents in the North Pacific divided into northern and southern, transients, and offshore. A great deal is known about residents which have been studied for 35 years. Little is known about the offshore animals that roam the open ocean, and extensive research is being done to learn more about and to identify transients.
At the Aquarium
Due to the space requirements for these intelligent and dynamic animals, we do not exhibit live whales or dolphins. Orcas (killer whales) are featured in Whales: a Journey with Giants (a large-scale multimedia presentation), signage and in the Passport, a visitor’s guide.
Mostly sporadic in all regions of the world ocean, from tropical to temperate zones to the edge of polar ice packs. Small concentrations off Antarctica, northern Japan, Iceland, Norway, Alaska, Washington, and British Columbia.
Although found in tropical and offshore waters, orcas prefer cooler coastal waters no more than 800 km (497 mi) from major continents. Resident pods have established territories with fairly predictable patterns of movements within their territories as they follow prey. They are known to spend time in brackish water and even rivers. Transients do not establish territories nor do they move predictably. Offshore orcas are seldom in protected inshore waters, spending most of their time in the open ocean on the continental shelf.
Orcas have a stout body that is tapered at both ends (fusiform). They have a round blunt head and lack the distinctive beak that dolphins usually have. The mouth line is straight. They have large broad, rounded, and paddle-shaped pectoral fins (flippers) that can be 1.8 m (6 ft) long and 0.9 m (3 ft) wide. Their flukes have a distinct notch in the center, slightly concave trailing edges, and may have pointed tips.
These whales differ in the shape of their dorsal fin and saddlepatch. The tip of the dorsal fin of resident females and immature males is rounded ending in a sharp corner. The leading edge tends to be slightly curved back. That of mature males is straight and more triangular in shape. The saddlepatch of residents is either uniform in color, or may be open containing varying amounts of black pigment. Typically, transients have a fin that has a more pointed tip (closely resembling that of a shark). There is often a bulge at the midpoint of the trailing edge. Their uniformly gray saddlepatch is quite large and never open. Offshore orcas have a dorsal fin that is continually rounded over the entire tip and a saddlepatch that is often open.
The black and white coloration of orcas is both striking and distinctive. Their jet-black body has sharply defined white areas on the belly, flanks, chin, and throat. They have oval white eyepatches behind and above each eye. Their flippers and fins are usually all black while the underside of their tail flukes is white. There is a prominent usually grayish saddlepatch behind the dorsal fin.
Male orcas are 5.8-6.7 m (19 to 22 ft) in length and weigh 3628 to 5442 kg (8000 to 12,000 lb). The smaller females are 4.9-5.8 m (16 to 19 ft) long and weigh 1360 to 3628 kg (3000 to 8000 lb). The dorsal fin of males, especially older ones, can be as high as 1.8 m (6 ft) whereas that of females are much shorter, 0.9-1.2 m (3-4 ft). The pectoral fins and flukes of males are also larger than those of females.
Diet and Feeding
These dolphins have 40 to 56 conical-shaped teeth that curve slightly backward and inward. Each tooth is about 7.6 cm (3 in) long. They swallow smaller prey whole and use their interlocking upper and lower teeth to grip larger items in order to tear them into pieces small enough to swallow. Unlike the baseball-sized throat of baleen whales, this toothed whale’s throat is large enough to swallow small seals whole. They use their excellent above and below water eyesight to find prey. In addition, residents and offshore orcas use echolocation to search for a meal.
Like other toothed whales, orcas have a fat-filled organ called a melon which acts like a lens to focus sounds in front of the whale. The whale sends out high-pitched rapid clicks (as many as several hundred per second) that are produced in nasal sacs behind its blowhole and listens for echoes to come back as they bounce off of objects such as prey. The stealthy transients do not echolocate when hunting. They use passive listening to locate prey, staying mostly silent to avoid being heard by their intended meal. However, they vocalize with whistles, squeals, and squeaks during the attack and directly after the kill.
Cooperative hunting is common among all populations, but food preferences are not. Resident orcas are fish-eaters with a strong preference for salmon, timing their movements within their territories with salmon runs. Transients hunt a wide range of prey. They have a preference for harbor seals, but also eat California and Steller sea lions, Dall’s porpoise, dolphins, small whales (narwhal, beluga, gray whale calves), squid, sharks including the great white, seabirds, and even moose and deer encountered swimming across narrow channels. In recent years because of the decline in seals and sea lions in parts of Alaska, they have begun to prey on sea otters. Offshore orcas are believed to be primarily fish and squid eaters but details about their diet are sketchy. Researchers believe that they may also prey on sharks because of the much greater number of scars and nicks on their bodies than on other populations.
Females become sexually mature at 12 to 16 years of age and males at about 10 to 17. Although the territories of populations overlap, they do not interbreed. Based on DNA evidence, males almost always mate with females outside of their pods reducing the risk of inbreeding. In the wild females calve about every five years and stop reproducing when they are 40 years old. The gestation period is usually about 17 months, the longest of all known cetaceans. Newborn calves are 2.1 to 2.5 m (7-8 ft) in length and weigh 136 to 181 kg (300 to 400 lb). The mortality rate from birth to six months is 37 to 50%. Why it is so high is unknown.
A calf’s upper teeth start erupting at two to three months of age at which time they start taking solid food such as fish from the mother. The lower teeth erupt at four months, however, they continue to nurse until they are one to two years old. Their first sounds are high pitched screams and at two months they begin to vocalize with pulsed calls believed to be learned from the mother. They learn foraging skills and social behaviors from pod members.
Resident orcas indulge in a number of social behaviors very similar in type and number to that of humpbacks: breaching, flipper slapping, tail lobbing, and splashing at the surface. They also chase, head stand, and play with objects such as kelp and sea jellies. While socializing, they are especially vocal emitting a wide range of whistles and calls seldom heard at other times. Transients are not as acrobatic.
These dolphins are believed to be one of the fastest swimming marine mammals. They cruise at 3.2-9.7 kph (2-6 mph) but can accelerate to 48 kph (30 mph) for short bursts.
Preparing to dive, they take 2-5 breaths at 5-10 second intervals and dive for 10 to 15 seconds. After 3-5 short dives, they take a longer dive that lasts for 1-4 minutes.
Orcas have a complex social structure of subpods, pods, clans, communities, and herds. The pods or groups are usually made up of several females, calves, and one to two males. There may or may not be juveniles in the pod. Each pod produces a specific number and type of calls, a dialect. Some of the calls are unique to the pod while others are shared and form the basis for a language group called a clan.
The resident pods, numbering 5 to 50 individuals, are matrilineal, that is, there is a family structure of a mother and her sons and daughters who usually remain with her for life and the several generations travel together. Transients travel in small loose groups of two to six individuals, usually in close proximity. The groups are more fluid and often contain unrelated females with offspring that do not remain with their mothers. Researchers believe the transient groups form as temporary foraging packs. It has been determined that there are 30 to 60 whales in offshore groups but the social structure is still being studied.
The maximum lifespan of female orcas in the wild is believed to be 80 to 90 years with an average of 63 years. Males have a shorter maximum lifespan of 50 to 60 years, averaging 36. Orcas in protected environments do not live as long.
Native peoples of coastal regions regarded orcas, not with hostility, but with awe and respect. They figured prominently (and still do) in their storytelling and art as evidenced by the colorful figures portrayed on totem poles. Some considered them to be the custodians of the sea from which they would give people gifts of strength, food, and health. On the other hand they were regarded by non-natives as blood thirsty, voracious predators extremely dangerous to humans. As late as 1973, the U.S. Navy’s diving manuals described orcas as extremely ferocious warning that they “will attack human beings at every opportunity.” Now we know that the only attacks on humans have been those made on trainers in theme parks where the animals perform. In British Columbia and Norway, orcas were shot on sight because they were believed to compete with humans for herring and salmon. Since the yield of oil from an orca was only 4.4-5.6 barrels in contrast to the 30 to 45 barrels from a sperm whale, orcas were not a target of whalers.
As top predators in their ecosytems, orcas have no natural predators. They are, however, faced with man-made threats. A major one is toxic pollution from organochlorides such as PCBs, DDT, and dioxins. The level of PCBs in both the southern and northern resident populations measures 100 parts per million, far greater than the danger level estimate of 17 parts per million for negative impacts on the immune and reproductive systems of harbor seals. Other threats include declining prey availability, especially of salmon, caused by overfishing and habitat loss, perception by members of the fishing industry that orcas are the reason for the declines of fish, impacts of noise pollution from increasing shipping and sonar testing by the military, entanglement in fishing gear, and effects of growing recreational and commercial whale watching boats, a concern not shared by all researchers but being studied.
The IWC classifies orcas as small cetaceans and does not manage them except for prohibiting commercial whaling. Under Canada’s Species at Risk Act, the southern residents are listed as endangered, northern residents and transients as threatened, and the offshore as species of special concern. In the United States orcas are protected under the MMPA and the southern resident population has recently been listed as threatened under the ESA.
Who’s on top? Orcas use acrobatic and other behaviors to communicate dominance and position in their social groups. They slap their tail against the water, butt heads, snap jaws, bite, tooth-scratch, and engage in other vigorous postures and gestures. Tooth scratches may be deep enough to leave permanent scars. Mothers discipline their calves by corralling them and by tooth-scratching.
No need for hearing aids: Orcas have exceptional hearing ability. Humans perceive sound in a range of 0.02-17 kHz whereas orcas can hear in a range of 0.5 to 125 kHz. Their sound perception is believed to be through their fat-filled lower jaw and also the soft tissue and bone surrounded the ear. The jawbone conducts sound waves through the jaw to the middle ear, inner ear, and then to hearing centers in the brain via auditory nerves.
Rubbing beaches: Northern resident orcas exhibit a behavior not shown by the southern residents. They have identified a number of pebble-strewn shallow waters and beaches where they swim into the very shallow waters, even beaching themselves, to rub their body against the pebbles, often for a long period. The reason for this unique to the northern residents behavior is unknown.