Diet: The array of species on which orcas prey is extremely diverse. Specific populations tend to specialize on particular prey species, even at the expense of ignoring other potential prey. For example, some populations in the Norwegian and Greenland sea specialise on herring and follow that fish's migratory path to the Norwegian coast each autumn. Other populations in the area prey on seals. Orcas are the only mammals with this diversification of feeding among overlapping species.
The orca is the only cetacean species to regularly prey on other cetaceans. Twenty-two species have been recorded as preyed on, either through an examination of stomach contents, examining scarring on the other cetacean's body, or by simply observing the feeding activity. Pods of orcas will even prey upon larger whales such as Fin Whales, Minke Whales, Grey Whales, or even young Blue Whales. A group of orcas take a young Blue Whale by chasing it and its mother through the sea, wearing them out. Eventually the orcas manage to separate the pair and then surround the younger whale, thereby preventing it from returning to the sea's surface in order to breathe. Once the whale has drowned, the orcas are free to feed on it.
There has also been one recorded case of probable orca cannibalism. A study carried out by V. I. Shevenko in the temperate areas of the South Pacific in 1975 recorded two male orca whose stomachs contained the remains of other orcas. Of the 30 orcas captured and examined in this survey, 11 had empty stomachs — an unusually high percentage that indicates the orca were forced to cannibalism through a lack of food.
More commonly, orcas prey on 30 species of fish, particularly salmon, herring, tuna, chinook and coho. Basking sharks, oceanic whitetip sharks, and very occasionally even great white sharks are taken for their nutrient-rich livers. There is also believed to be an element of competition elimination in taking these sharks. Other marine mammals, including most species of seal and sea lion, are also taken by polar populations. Walrus and sea otters are taken less frequently. Seven species of bird are also taken, including all penguin species as well as sea birds such as cormorants. Cephalopods, such as octopi and a wide range of squid, are also targets.
Orcas are very inventive and playful in their killing. They sometimes will throw seals to one another through the air in order to stun and kill the animal. While salmon are usually hunted by a single orca or a small group of individuals, herring are often caught using carousel feeding: the orcas force the herring into a tight ball by releasing bursts of bubbles or flashing their white underside. The orcas then slap the ball with their tail flukes, either stunning or killing up to 10-15 herring with a successful slap. The herring are then eaten one at a time. Carousel feeding has only been documented in the Norwegian killer whale population and with some oceanic dolphin species. Sea lions are killed by head-butting or by being slapped and stunned by a tail fluke.
More specialized feeding techniques are used by various populations around the world. In Patagonia, orcas feed on southern sea lion and elephant seal pups by forcing them on to beaches, even to the extent of stranding themselves, albeit temporarily. Orcas will spy-hop to locate seals resting on ice floes, and then create a wave to wash over the floe, causing the seal to be thrown into the water where a second orca waits to kill it.
On average, the orca eats 60 kg of food each day. With this huge variety of prey, and no predators other than man, the orca is very much at the top of the food chain.
Orcas in history: Although only scientifically identified as species in 1758, the orca has been known to man since prehistoric times. The desert culture of Nazca created a Nazca line representing an orca sometime between 200 BC and AD 600.
The first description of an orca is given in Pliny the Elder's Natural History (written circa 50 BC). The aura of invincibility around the all-consuming orca was well-established by this time. Having watched the public slaughtering of a whale stranded at a harbor near Rome, Pliny writes, "Orcas, (the appearance of which no depiction can express, other than an enormous mass of savage flesh with teeth), are the enemy of [other whales]... charge and pierce them like warships ramming."
Aboriginal tribes of the American Pacific Northwest such as the Tlingit, Haida, and Tsimshian featured the orca prominently in their religion and artwork.
Orcas and modern man:
Orcas were targeted in commercial whaling for the middle part of the twentieth century once stocks of larger species had been depleted. Commercial hunting of orcas came to an abrupt halt in 1981 with the introduction of the moratorium on all whaling. (Although from a taxonomic point of view an orca is a dolphin rather than a whale, it is sufficiently large to come under the purview of the International Whaling Commission.)
The greatest hunter of orcas was Norway which took an average of 56 animals per year from 1938 to 1981. Japan took an average of 43 animals from 1946 to 1981. (War year figures are not available but are likely to be far fewer). The Soviet Union took a few animals each year in the Antarctic, with the extraordinary exception of the 1980 season when it took 916.
Today, no country carries out a substantial hunt. Japan usually takes a few individuals each year as part of its controversial program of "scientific research." A similarly small level of subsistence whaling is carried out by Indonesia and Greenland. As well as hunting for their meat, orcas have also been killed because of their competition with fishermen. In the 1950s the U.S. Air Force, at the request of the Icelandic government, used bombers and riflemen to slaughter orcas in Icelandic waters because they competed with humans for fish. The operation was considered a great success at the time by fishermen and the Icelandic government. However, many were unconvinced that orcas were responsible for the drop in fish stocks, blaming overfishing by humans instead. This debate has led to repeated studies of North Atlantic fish stocks, with neither side in the whaling debate giving ground since that time.
The orca is also occasionally killed out of fear of its reputation. No human has ever been attacked by an orca in the wild, but sailors in Alaska shoot the animal occasionally with concern for their own lives. This fear has generally dissipated in recent years due to better education about the species, including the appearance of orcas in aquariums and other aquatic attractions.
The orca's intelligence, trainability, striking appearance, playfulness in captivity, and its sheer size have made it a popular exhibit at aquariums and other aquatic attractions such as aquatic theme parks. The first orca capture and display took place in Vancouver in 1964. Over the next 15 years around sixty or seventy orcas were taken from Pacific waters for this purpose. In the late 1970s and the first half of the 1980s, orcas were generally taken from Icelandic waters (fifty in the five years to 1985). Since that time, orcas have been successfully bred in captivity and wild specimens are considerably rarer. Orcas in captivity may develop pathologies such as dorsal fin collapse, seen in 60-90% of captive males.
There have been incidents with orcas in captivity attacking humans. In 1991, a group of orcas killed a trainer named Keltie Byrne at Sealand in Victoria, British Columbia (where employees were not allowed in the water with orcas), apparently not knowing she could not survive underwater. In 1999, at the SeaWorld park in Orlando, Florida, one of the same orcas allegedly killed a tourist who had sneaked into the orca's pool at night (http://www.cnn.com/US/9907/06/killer.whale/). (The tourist was also thought to be a victim of hypothermia.) In late July 2004, during a show at the SeaWorld park in San Antonio, Texas, an orca pushed its trainer of ten years underwater and barred the way to the rim of the pool; the trainer could only be rescued from the raging animal after several minutes.
One of the more infamous incidents involving orca aggression took place in August 1989, when, during a live show, one female whale, Kandu V (who had established herself as the dominant female) struck another whale, Corky II, imported from Marineworld California just months prior to the incident. According to reports, a loud smack was heard across the stadium. Although trainers tried to keep the show rolling, the blow severed an artery near Kandu V's jaw, and she began spouting blood. The crowd was quickly ushered out, and after a 45-minute hemorrhage, Kandu V died. Opponents of these shows see these incidents as supporting their criticism.
SeaWorld continued to be implicated in unfair practices by keeping orcas taken from the wild, and came under criticism from the Born Free Foundation over its continued captivity of the orca Corky, who they want to be returned to its family in the A5 Pod—a large pod of orcas in British Columbia, Canada.
As late as the 1970s, orcas were depicted negatively in fiction as ravenous predators whose behavior caused heroes to interfere to help a prey animal escape. The most extreme example is the poorly received film Orca which featured the story of an orca going on a vengeful rampage after its mate is killed by humans (in an obvious attempt to copy the success of Jaws).
However, the increased research of the animal and its popularity in public venues brought about a dramatic rehabilitation of the animal's public image. The sentiment about the animal grew to more as a respected predator that poses little actual threat to humans, much as the North American wolf's image has been changed.
The movie Free Willy (1993) focused on the quest for freedom for a captive orca. The whale starring in the movie, Keiko, was originally caught in Icelandic waters. After rehabilitation at the Oregon Coast Aquarium in Newport, Oregon, he was later returned to the waters of the Nordic countries, his native habitat, but continued to be dependent on humans until his death in December 2003.
The Exxon Valdez oil spill had a particularly adverse effect on the Alaskan orca population. One pod was caught in the spill; though the pod successfully swam to clear water, eleven members of the pod (about half) died in the following days and weeks. The spill had a longer-term effect in reducing the amount of available prey, such as salmon, and has thus been responsible for a local population decline. In December 2004, scientists at the North Gulf Oceanic Society said that the pod (called the AT1 pod) now only came to seven in number, having failed to reproduce at all since the spill. The population is expected to become completely extinct. Press Telegram report on the pod
Like other animals at the highest trophic levels of the food chain, the orca is particularly susceptible to poisoning via accumulation of Polychlorinated biphenyls (PCBs) in the body. A survey of animals off the Washington coast found that PCB levels in orcas were higher than those in harbour seals in Europe (what have been sickened by the chemical). However, no direct evidence of sickness in orcas has been found. The most likely effect, if any, would be a reduced rate of reproduction.
Other environmental pressures facing orcas include extensive whale-watching which some research indicates changes whale behavior. Heavy ship noise has caused some groups of orca to change the frequencies of their songs and calls.
References: Orca: The Whale Called Killer, Erich Hoyt, Camden House Publishing.
Killer Whale, John K.B. Ford, pp669–675 in the Encyclopedia of Marine Mammals, Academic Press.
National Audubon Society Guide to Marine Mammals of the World, Reeves, Stewart, Clapham and Powell. Alfred A. Knopf.
Kharakter vzaimootnoshenii kasatok i drugikh kitoobraznykh in Morskie mlekopitayushchie
(in Russian, transliterations vary). The nature of interrelationships between
Killer Whales and Other Cetaceans I.V.Shevchenko, 1975 pp173–175. (The
author describes his discovery of orca cannibalism).