Orcinus orca

Orcinus orca

The orca or killer whale (Orcinus orca Linnaeus, 1758) is a marine mammal belonging to the Delphinidae family.

Systematics –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Superphylum Deuterostomia,
Phylum Chordata,
Subphylum Vertebrata,
Infraphylum Gnathostomata,
Superclass Tetrapoda,
Mammalia class,
Subclass Theria,
Infraclass Eutheria,
Superorder Laurasiatheria,
Order Cetartiodactyla,
Suborder Odontoceti,
family Delphinidae,
Subfamily Orcininae,
Genus Orcinus,
Species O. orca.
The term is basionym:
– Delphinus orca Linnaeus, 1758.
The terms are synonyms:
– Delphinus duhameli Lacépède, 1804;
– Delphinus gladiator Bonnaterre, 1789;
– Delphinus grampus Blainville, 1817;
– Delphinus grampus Desmarest, 1817;
– Delphinus orca subsp. ensidoratus Kerr, 1792;
– Delphinus serra Borowski, 1780;
– Delphinus victorini Grill, 1858;
– Grampus orca Iredale & Troughton, 1933;
– Grampus rectipinna Scheffer, 1942;
– Grampus vectipinna Branson, 1971;
– Ophysia pacifica Gray, 1870;
– Orca africana Gray, 1871;
– Orca antarctica Fischer, 1876;
– Orca ater Cope, 1869;
– Orca ater subsp. fusca Dall, 1874;
– Orca atra Gray, 1871;
– Orca capensis Gray, 1846;
– Orca eschrichtii Reinhardt, 1866;
– Orca glacialis Berzin & Vladimirov, 1982;
– Orca gladiator Bonnaterre, 1789;
– Orca gladiator Van Beneden & Gervais, 1869-1880;
– Orca gladiator subsp. arcticus Gervais, 1869-1871;
– Orca gladiator subsp. australis Gervais, 1869-1871;
– Orca gladiator subsp. europaeus Gervais, 1869-1871;
– Orca gladiator subsp. tasmaniensis Cabrera, 1961;
– Orca latirostris Gray, 1870;
– Orca megellanica Burmeister, 1866;
– Orca minor Malm, 1871;
– Orca orca Lahille, 1914;
– Orca orca subsp. megallanicus;
– Orca pacifica Gray, 1870;
– Orca rectipinna Cope, 1869;
– Orca schlegelii Lilljeborg, 1866;
– Orca stenorhyncha Gray, 1870;
– Orca tasmanica Gray, 1871;
– Orcinus glacialis Berzin & Vladimirov, 1983;
– Orcinus morzerbruynsus Heintzelman, 1981;
– Orcinus nanus Mikhalev & Ivashin, 1981;
– Orcinus orca subsp. capensis Trouessart, 1904;
– Orcinus orca subsp. eschrichti Trouessart, 1904;
– Orcinus orca subsp. magellanica (Burmeister, 1866);
– Orcinus orca subsp. megallanicus Trouessart, 1904;
– Orcinus orca subsp. pacifica (Gray, 1870);
– Orcinus rectipinna (Scammon & Cope, 1869);
– Phocaena orca (Linnaeus, 1758);
– Physeter microps Fabricius, 1780.

Geographic Distribution and Habitat –
The Orcinus orca is a mammal that is widespread in all the seas and oceans of the world and lives both in the abyss and in the slums near the coasts, sometimes even reaching the mouths of some rivers.
Due to the enormous extension of the distribution area, number and density, the relative distribution is difficult to estimate. Killer whales, however, clearly prefer higher latitudes and coastal areas over pelagic environments. The areas that serve as important study sites for the species are mainly the coasts of Iceland, Norway, the Valdes peninsula in Argentina, the Crozet Islands, New Zealand and parts of the western coast of North America, from California to Alaska.
Systematic surveys indicate the highest densities of orcas (> 0.40 individuals per 100 km2) in the northeastern Atlantic around the Norwegian coast, in the North Pacific along the Aleutian Islands, the Gulf of Alaska and in the Southern Ocean off of much of the coast of Antarctica. They are considered “common” (0.20-0.40 individuals per 100 km2) in the eastern Pacific along the coasts of British Columbia, Washington and Oregon, in the North Atlantic Ocean around Iceland and the Faroe Islands.
As for Antarctica, orcas range right to the edge of the pack ice and are believed to venture into denser pack ice, finding open hollows just like beluga whales in the Arctic. However, orcas are only seasonal visitors to Arctic waters and do not approach the ice floe in the summer. With the rapid decline of Arctic sea ice in the Hudson Strait, their range now extends deep into the northwest Atlantic. Occasionally, killer whales swim in freshwater rivers. They have been documented 160 km up the Columbia River in the United States. They have also been found in the Fraser River in Canada and the Horikawa River in Japan.
On the other hand, sightings in the Mediterranean Sea are rare. Several killer whales were sighted in the Ligurian Sea near Pra’ in December 2019; at first it was thought they came from a pod of orcas that has lived for some time near the Strait of Gibraltar, but then it was understood that it was a group known and filed in Iceland. The researchers of the Orca Guardians Iceland association exchanged their data with Ligurian biologists and it was discovered from the comparison of the fins and other details that these were specimens studied in 2017.
Instead, the migration models are poorly understood.
In general, its marine habitat is that of cold Arctic and Antarctic waters where, in summer, the orca hunts among the ice floes. Only a few populations migrate toward the equator in the summer, much like gray whales that migrate near US shores.

Description –
Orcinus orca is the largest extant member of the dolphin family.
Males range from 6 to 8 meters in length and weigh more than 6 tons. However, the largest recorded specimen measured 9.8 meters and weighed more than 10 tons. Females are smaller, generally ranging from 5 to 7 m and weighing 3 to 4 tons. At birth, the cubs weigh about 180 kg and are about 2.4 m long. The orca’s skeleton is typical of an oceanic dolphin, but more robust.
They have a distinctive pigmentation whereby adult killer whales are rarely confused with any other species.
The orca typically has a starkly contrasting black and white body; being mostly black above and white below. The entire lower jaw is white and from here the coloration extends across the underside to the genital area; narrowing between fins, then widening somewhat and extending in lateral patches on flanks near tip. The tail fin is also white underneath, while the eyes have white oval-shaped patches behind and above them, and a gray or white “saddle patch” exists behind the dorsal fin and on the back.
Males and females also have different black and white skin patterns in the genital areas.
In newborns, the white areas are yellow or orange.
Antarctic killer whales can have pale gray to almost white backs. Also some Antarctic killer whales are brown and yellow due to diatoms in the water.
Finally, both albino and melanistic killer whales have been documented.
The orca’s pectoral fins are large and rounded, paddle-like, with those of males significantly larger than those of females. The dorsal fins also show sexual dimorphism, with those of the males about 1.8 m tall, more than double those of the female, with the male’s fin more resembling an elongated isosceles triangle, while that of the female is more curved.
In the skull, adult males have longer lower jaws than females, as well as larger occipital crests.
The snout is blunt and lacks the beak of other species.
The orca’s teeth are very strong and its jaws exert a powerful grip; the upper teeth fall into the spaces between the lower teeth when the mouth is closed. The solid central and rear teeth hold the prey in place, while the front teeth are angled slightly forward and out to protect them from powerful jerking movements.
In addition, orcas have good eyesight both above and below water, excellent hearing and a good sense of touch.
They possess an exceptionally sophisticated echolocation ability, sensing the location and characteristics of prey and other objects in the water by making clicks and listening for echoes, as do other members of the dolphin family.
The average body temperature of the orca ranges from 36 to 38 °C.
Like most marine mammals, orcas have an insulating blubber layer that is 3 to 4 inches thick under their skin.
The pulse is around 60 beats per minute when the orca is on the surface, dropping to 30 beats per minute when submerged.
Different types of killer whales have also been recognized based on their morphology and behavior, whereby, based on their mitochondrial DNA, some have proposed that they are different species or, failing that, that they are at least different races.
In the 1970s and 1980s, research conducted off the west coast of Canada and the United States identified three types of killer whales, namely:
– resident, transient and maritime.
Although these populations share some areas of their range, they show considerable genetic difference, which shows that they do not interbreed with each other. The three types differ substantially in their ecology, behavior and morphology.
As regards the differentiation of these three types, the following is reported:
– Residents: they are the most frequently observed killer whales in the coastal areas east of the North Pacific in the waters of Canada and the United States; they inhabit this area year-round and migrate shorter distances than transients. Four such communities are known in the area: Southern, Northern, Southern, and Western Alaska. They feed mainly on fish, especially salmon, and occasionally on squid. They live in complex family groups (called in English pods) consisting of six to sixty individuals. They differ from the other types, the transient and maritime ones, in the shape of the dorsal fin which describes a curve and is rounded in tip, tip, and vocalization patterns. The communities that are part of this type of orca are highly inbred, i.e. mating occurs only between individuals within their community.
– Transient: this type of killer whale associates in smaller pods than the sedentary ones, moving more frequently in groups of less than ten specimens. They have a less rigid social organization than the sedentary ones and they don’t feed on fish; their diet is mainly based on marine mammals. It has a wider distribution area than the residents and migrates over greater distances than the latter. They have less varied vocalizations, less complex dialects, and make sounds only 5% of the time. They also have morphological differences compared to sedentary and maritime ones, since unlike these they have a triangular dorsal fin ending in a point.
– Maritimes: this group was first described in 1988, when they were observed in the open ocean. They are usually found more than 15 km from the coast, although they sometimes approach it. They are grouped in herds of twenty to seventy-five individuals. Until recently their diet was thought to consist mainly of fish and it was thought that, due to the presence of scars and incisions on their dorsal fins similar to those seen in transients, they also fed on marine mammals and possibly sharks. However, according to a study published in 2011, their diet appears to be based primarily on sharks and they frequently do so from species in the genus Somniosus. This type of killer whale is slightly smaller than the other two types and the tips of its dorsal fin, as in the residents, are rounded.
Resident and passing orcas share some areas, but are generally avoided. Based on DNA analysis of the skin samples, it was concluded that the two groups had separated by at least 10,000 years.
Additionally, four types of killer whales have been described in Antarctica:
– Type A: The size of an average killer whale with a black and white color pattern and a medium-sized eye patch. It lives in open waters and feeds almost exclusively on fin whales (Balaenoptera bonaerensis).
– Type B: it is smaller than type A; the white spot of the ocular region is large, the white parts have a yellowish tint and the dark areas instead of being black have a grayish tint. It has a large light gray patch extending from the head to the dorsal fin. Their diet consists mainly of seals.
– Type C: The killer whale of this type is the smallest and the one that lives in larger groups. The white patch in the eye region is oriented obliquely and forward, rather than parallel to the axis of the body. Like those of type B, it has a large gray patch on its back and the white areas have a yellowish tinge. They have been observed feeding on Antarctic cod (Dissostichus mawsoni).
– Type D: Described based on photographic analysis of a 1955 mass stranding in New Zealand and observations made since 2004. It is the most diverse type of killer whale in its appearance and can be instantly recognized by its very small patch on the eye. Its range appears to be circumpolar over Antarctic waters between 40° and 60°
south latitude. Aggregations appear to be large with an average of 17.6 members and a range of 9-35 animals. Its diet is unknown, but fish is suspected, as they have been observed in the vicinity of longliners and predation on southern cod (Dissostichus eleginoides) has been documented.
Types B and C live near ice caps and the yellowish coloration of their white parts is due to the presence of diatom algae in Antarctic waters.
Mitochondrial DNA studies appear to support the hypothesis that the types of killer whales described in Antarctica are different species that have recently diverged; however, the results are not conclusive. Other studies of complete mitochondrial sequences suggest that Antarctic types B and C could be recognized as different species, as well as transients from the North Pacific. Under that assumption, the other orca types would remain as subspecies pending further data.
However, orca populations in other parts of the world have not been studied in sufficient detail to distinguish other types. Be that as it may, there seem to be similarities with the typologies described by comparing their eating habits and the characteristics of the social relationship they possess. For example, the fish-eating population inhabiting Norwegian waters has a family structure similar to that of resident orcas in North America, and the mammal and bird-eating orcas in Argentina and the Crozet Islands are more similar.

Biology –
While orcas are widespread animals, there are no field studies available on all aspects of the species’ reproductive behavior and much of the available information comes from captive animals.
However, it is known that females become sexually mature when they reach a length of between 4.6 and 4.9 m and an age between six and ten years. Males mature when they reach a size between 5.5 and 6.1 m in length and between 10 and 13 years of age. The greater growth of the dorsal fin in males compared to females probably constitutes a secondary sexual characteristic, since the higher growth rate coincides with the arrival of sexual maturity.
It has been noted, in the observation of captive females, that they have periods of several heat cycles interspersed with periods of ovulatory inactivity. These heat periods average four cycles at a time, are variable and unpredictable, and are different for each female. There is no noticeable menstrual blood loss during these cycles.
Even in captivity it has been documented that males can court a female in heat for five to ten days. They have been seen to mate with pregnant females and also with females that are not in heat. Males are polygamous and always reproduce outside their herd reducing the risk of inbreeding. The difference in dialects will most likely help them determine the degree of family relationship of a potential mate.
The gestation period varies between fifteen and eighteen months. In captivity the average recorded is seventeen months (517 ± 20 days) with a range of 468-539 days.
For each birth the female gives birth to a pup, with a period between each birth of 5.3 years on average, with a range of two to fourteen years in the animals of the Northeastern Pacific and 3 and 8.3 years respectively in the North Atlantic and Antarctica. In captivity they reproduce at intervals of 2.7 to 4.8 years. However, one female has been documented to have had a calf nineteen months after the death of her previous newborn.
Births occur at any time of the year, more frequently during the winter. Mortality is high during the first six months of life, with a mortality rate of 37 to 50%. In its natural environment, nursing lasts about five minutes and takes place on the surface or under water. Captive hatchlings have been observed feeding thirty-two to thirty-four times a day, with a total time invested of 3.2 to 3.6 hours a day; the average duration of feeding sessions is 6.8-7.2 minutes. Weaning begins at one year of age and is completed at two years of age. Females who have not reached childbearing age, and sometimes males, participate in caring for the young.
In puppies, tooth eruption begins at eleven weeks of age, at which time they begin consuming solid food provided by their mothers. In young specimens in captivity, there is a consumption of 6.6 kg of fish and squid at five months of age and 22 kg at fifteen months.
Orca calves stay with their mothers even after they reach adulthood. These help them in finding a partner, to make sure they have offspring.

Ecological role –
The Orcinus orca is the only extant species recognized in the genus Orcinus, one of the many animal species described by Linnaeus in the Systema Naturae of 1758. The first scientific description of an orca is found in Piscium & aquatilium animantium natura, a writing by Conrad Gessner from 1558, based on the examination of a specimen that died after being stranded in the Gulf of Greifswald.
This species is one of the 37 of the delphinidae family, whose first appearance dates back to about 11 million years ago; the phylogenetic detachment of the orca occurred about 5 million years ago.
The orca is the marine mammal that can swim the fastest and reach speeds of 55 km/h. Its speed is mainly given by the powerful thrust of its muscular tail. The bite force is very poor for its size, this is because it uses its teeth as blades to cut through fat and flesh rather than applying pressure. The jaws generate a force of 7000 N (700 kg force) per 47 kg/cm2.
The orca is a major predator in all of the world’s oceans. It consumes a wide variety of prey items, mainly fish and marine mammals. The different types and populations have a specialized diet throughout the year. For example, some groups in Norway and Greenland feed almost exclusively on herring (Clupea); while other orca populations in the same area feed only on seals; the resident killer whale population in the North Pacific feeds on 96% salmon, of which 65% is king salmon (Oncorhynchus tshawytscha). Initially, the information on the type of food ingested came from the stomachs of stranded or hunted animals, subsequently direct observation has provided further data on their eating habits.
Captive individuals eat about 3.6 to 4% of their body weight per day (about 160 kg for a 4-ton animal). Consumption gradually increases from birth to twenty years of age. For example, a captive female was recorded eating 22 kg of fish per day at one year of age, 45 kg at ten years of age and 56 kg at eighteen years of age. Due to the animals’ increased activity in the wild, they probably require a greater amount of food than captive individuals. The estimated daily caloric requirement is 85,000 kcal per day for younger youngsters, 100,000 for older ones, 160,000 for females and 200,000 for males. In free range animals, an average requirement of 62 kcal/kg/day has been reported.
Penguins and other seabirds are also part of their diet. In 1988, a new type of population called offshore was discovered in the open sea, which travels in groups of about 60 specimens but which can reach 200, genetically distinct from transients and residents. It is little known, although the Offshore females are recognized because they have stripes surrounding the fins. If the two populations of residents and transients frequent the same marine environment, they avoid reciprocal contacts.
The orca normally lives in groups consisting of the female, her young, older sterile females and an adult male. This is a matrilineal base family also called a pod.
All members of this family communicate with each other through sounds of various kinds and each pod has its own language. The orca has a specific organ on its forehead that it can use as sonar. All objects hit by sound waves send back an echo that orcas perceive as an animal or rock to be avoided.
Killer whales are highly social animals and hunting involves the whole group. The type of prey depends on the habits of the group: populations called residents are sedentary and essentially feed on fish. Transients, on the other hand, mainly hunt marine mammals such as seals, sea lions and even whales. During the hunt the transients become very silent, to take their preys by surprise, but the attack is well coordinated and each individual has a precise role.
In-depth studies have been able to highlight that some populations have developed peculiar hunting techniques. For example, the Argentine killer whales gather in February in front of the beaches where sea lions reproduce to hunt the still inexperienced pups. The technique is simple: an individual swims in front of the beach with the dorsal fin clearly visible above the surface of the sea thus making itself noticed, another individual, keeping underwater, crosses from the opposite direction.
If there are careless pups resting on the shoreline, the hidden killer whale swims towards the beach with impressive speed trying to capture its prey. In this enterprise the animal runs ashore, but with decisive movements of the body it slides back regaining the sea and carrying any prey with it. Antarctic killer whales, on the other hand, use waves to make seals slide off the ice: the matriarch goes to the opposite side of the iceberg to spot the seal and then warns the others with a signal. Then the rest of the pod swims at high speed to the iceberg causing a big wave and causing the seal to slip. New Zealand killer whales instead use a peculiar technique to capture stingrays, they lie belly up catching the stingray and then roll over causing the stingray to fall into a state of tonic immobility.
During their sea voyages, orcas often come into contact with other large predators of the sea. Encounters with mako, tiger and white sharks have been documented.
The orca also attacks and kills the walrus. The only animal capable of overpowering her is an adult sperm whale which, thanks to its diving ability, manages to escape her. Specimens not yet mature can instead be included in the diet of the killer whale itself.
As far as relationships with men are concerned, despite the reputation of ruthless predators they have possessed since the times of Pliny the Elder, attacks on humans are very rare in nature. On the other hand, there are some attacks, even fatal, which took place in captivity, probably under conditions of particular stress.
In recent years there has been an increase in cases of attacks on sailing boats near the Strait of Gibraltar and off the coast of Portugal, by a subgroup of sedentary or semi-sedentary killer whales. The precise causes are still unknown but turning off the electronic equipment, any engines and stopping usually stops the attack.
Estimates of world population are uncertain, but a recent consensus suggests a minimum of 50,000 (2006). Local estimates include about 25,000 in Antarctica, 8,500 in the tropical Pacific, 2,250-2,700 off the cooler northeastern Pacific, and 500-1,500 off Norway. The Japan Fisheries Agency estimated in the 2000s that 2,321 orcas were found in the seas around Japan.
The IUCN has not yet assessed the current conservation status of the orca because data is insufficient due to the likelihood that two or more types of orca are separate species. Some local populations are considered threatened or endangered due to the destruction of their habitat, pollution, their capture for use in marine parks and constant conflicts with fishermen.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Facilidad Global de Información sobre Biodiversidad.
– Gordon Corbet, Denys Ovenden, 2012. Guide to mammals of Europe. Franco Muzzio Publisher.
– John Woodward, Kim Dennis-Bryan, 2018. The Great Encyclopedia of Animals. Gribaudo Publisher.

Photo source:
– https://www.artsobservasjoner.no/MediaLibrary/2022/6/5fd3338b-9945-454f-a7e6-9d4b068859bf_image.jpg