Tale of Natsihlane
Long ago, in what is now south-eastern Alaska, a land rich in fish and fowl and furred creatures, Natsihlane, a skilled Tlingit Indian woodsman, went hunting with his brothers-in-law. All but the youngest were jealous of Natsihlane. They abandoned Natsihlane on a distant island, while the youngest despaired.
Natsihlane felt very sad and wondered if he would ever see his wife again. That night, a seagull came to him and flew with him to the home of the sea lions. Their chief put Natsihlane inside an inflated sea-lion stomach, laid it in the water, and instructed him to think hard about the beach near his village. He soon found himself there and began to plan revenge on his brothers-in-law. He got different pieces of wood and began to whittle blackfish. He tried spruce, then red cedar, then hemlock, painting each in stripes of different colours. But no amount of singing or shouting would bring them alive.
Finally, he carefully carved fine yellow cedar into eight large and small blackfish. He painted each with a white band across the head and a white circle on the dorsal fin. He sang his most powerful songs for them, commanding them to go. They swam about, and soon the bay was full of spray from their spouting and playing.
After many days, Natsihlane saw his brothers-in-laws' canoe far out at sea. He commanded the blackf'sh to destroy all but the youngest. They swam out and around and around the canoe. The men and the craft disappeared, but two blackfish saved the youngest brother-in-law and carried him towards the shore. Natsihlane called the blackflsh to him and said: 'When I made you I did not intend that you should kill human beings. I made you to get revenge on my brothers-in-law. Hereafter you shall not harm human beings but help them when they are in trouble. Now go.' And they swam out to sea, the first killer whales in the world.
Adapted by Heimlich-Boran J. & Heimlich-Boran S. from a Tlingit Indian folktale.
The Whale & the Eagle (from http://members.aol.com/stejacorca/whaleagl.htm)
Back in the time when Great Raven made things, animals roamed Earth in search for their place on it. High above soared Eagle with his black and white plumage. He was sad and lonely thinking he would never find a place amidst the world.
One day he was gliding along the waves of the ocean. Day after day he would play with his shadow atop the waters. Whale noticed the dark spot on the water and went to see what it was, for she had searched for someone to share her journey. She raised her head above the waves and called to Eagle. She spoke of how she had wandered the relative emptiness of the sea. Eagle and Whale spent every day at the ocean talking and sharing things each would bring from their worlds. They soon fell deeply in love, but grew more sad than ever before. For they were living in separate worlds.
One day when Eagle came at sunrise, Whale swam deep down, then she turned upwards and rushed to the surface until she broke through. While she was in mid-air they mated. Their children can still be seen and heard in the oceans today. They are the Orcas, the same colors as their father and breaching the water as their mother had that day when two worlds united in a love so strong that nothing could keep them apart.
Class: Mammalia (mammalians)
Order: Cetacea (cetaceans)
Sub-order: Odontoceti (toothed whales)
Familly: Delphinidae (dolphins and porpoises)
Sub-familly: Orcininae or Globicephalinae, along authors
Genus: Orcinus (FITZINGER, 1860)
Species: orca (LINNAEUS, 1758)
Common names: killer whale, swordfish, blackfish, Feegee fish, grampus, orca, orc, wolf of the sea mers), tiger of the sea, hyena of the sea, tyrant of the sea, orque (in French, feminine gender name), épaulard (in French), etc. The name "killer whale" arised from the predatory habits of the species, feeding on baleen whales and other dolphins. Early Spanish whalers referred to this animal as the "whale killer". Through the years, this was transposed to killer whale.
The Orcininae sub-familly would include:
The Globicephalinae sub-familly would include:
In the past, the killer whale has been classified as Orca gladiator (Bonnaterre, 1789), Orca rectipinna, Orca ater, Orca pacifica, Orca africana, Orca magellanicus, and many others (Heyning & Dahlheim, 1988).
More recently, scientists described two geographically separated killer whale species: Orcinus orca in the Atlantic Ocean and Orcinus rectipinna in the Pacific Ocean (Cope, 1869; Scammon, 1874; Scheffer, 1942).
Nowadays, the Orcinus orca classification (cf. above) is the most commonly admitted, killer whale being considered as the single highly variable and cosmoplitan representative of the Orcinus genus. However, with the accumulation of scientific data (morphology, behavior, genetic, ...) about orcas around the world, scientists suspect the existence of several species in the Orcinus genus. Indeed it appears that genetically disctinct populations exist (Hoelzel, 1989).
In 1981, Mikhalev et al. proposed to consider a species the inshore population of Antarctic Ocean, which individuals are smaller than the orcas of the northern hemisphere, and name it Orcinus nanus, or dwarf killer whale (project been refused by IWC by lack of informations).
Later, in 1982, Berzin and Vladimirov described a second dwarf Antarctic endemic species (Indian Ocean area), Orcinus glacialis. Orcinus nanus and Orcinus glacialis could be one single species described using two different classifications.
Today, it is accepted that at least 2 forms of orcas live in sympatry in the eastern North Pacific: the transients and the residents, this latter being composed of 3 communities (northern, southern and offshore communities) (Baird, 1999). Those two forms are assumed to be on the evolutionary path towards becoming distinct species (Ford, Ellis, & Balcomb, 1994). In 1992, Baird, Abrams and Dill brought the genetic evidence that transient and resident populations of eastern North Pacific did reproduce independantly from each other. Further studies will certainly give rise to new orcas species, subspecies or varieties, resulting from evolutive processes.
The fossil history of cetaceans stretches back tens of millions of years, and as with all other living species, the overall evolutionary picture is far from complete. Fossils unearthed at paleontological digs suggest that cetaceans evolved from a land-dwelling animal, the mesonyx (see drawing), belonging to the family Mesonychidae. Although wolf-like in appearance, this animal, which once roamed the primeval continents now known as Europe, Asia, and North America, is believed to have been related to other hoofed animals of that period. Recent molecular studies strongly suggest cetaceans may be directly descended from the hoofed relations of the modern-day sheep and cow. However, some scientists believe the horse may be the closest living relative of cetaceans. Whatever the animal that gave rise to modern cetaceans, whales, dolphins, and porpoises all descended from land mammals. (Adapted from Webster's Whales and Dolphins, 1998)
Numerous large delphinoid teeth, primarily from the Pliocene (-5.5 to -2 million years ago), have been attributed to species within the genus Orcinus. Such teeth have been reported from the Pliocene of Italy (Sarra, 1933) and Japan (Matsumoto, 1937). One of the few fossils represented by a good skull is O. citoniensis (Capellini, 1883) from the Pliocene of Italy. It appears to be a smaller species than O. orca with an estimated total length of less than 4 m. O. citoniensis has a slightly higher tooth count (14/14) and proportionately smaller teeth than the extant species. In these characters, O. citoniensis seems to be intermediate between the more typical delphinids and O. orca (Pilleri and Pilleri, 1982).
Orcas skull can be distinguished from the one of another species by its large size (condylbasal length to 100 cm), the dental formula (10 to 14 / 10 to 14, so 40-56 teeth in all) and large teeth, except from a large false killer whale skull (dental formula 8 to 11 / 8 to 11) (Leatherwood et al., 1982). Skulls of killer whales can be distinguished from those of false killer whales by the width across the premaxillaries being less than 50% of rostral width just anterior of antorbital notches and the lateral border of the premaxillaries being slightly more sigmoid in dorsal view and wider distally (Heyning and Dahlheim, 1988). Pterygoids widely separated and teeth compressed anteroposteriorly at the roots are two characteristics often cited as diagnostic for orcas (Glass, 1974), but do not always separate orcas and false killer whales.
The tympano-periotic bone complex of
killer whales is characterized by a lack of a ventral keel, closure of the elliptical
foramen, and massive anterior and posterior processes of the periotic (Kasuya,
Female killer whales generally attain a body length of 7.0 m and males
8.2 m (Mitchell, 1975). Perrin and Reilly (1984) reported maximum lengths
of 8.5 m for females and 9.8 m for males.
For the few weighted killer whales maximum recorded mass was 3,100 kg for a 6.35 m female and 4,000 kg for a 6.04 m male (Hoyt, 1981).
The blunt head has virtually no distinguishable beak. The relatively and absolutely large ovate flippers are positioned about one-fourth the distance from the snout to flukes and contrast with the sickle-shaped flippers of most delphinids. Males flippers may measure 2 m long (Harmer, 1927) and attain 20% of the body length; females flippers reach 11 to 13% of the body length (Eschricht, 1866). The dorsal fin of adult males is triangular reaching 1.8 m high, whereas in adult females and young males it is smaller reaching 0.9 m and is distinctly falcate. Adult males can be easily distinguished in a pod thanks to their tall dorsal fin, but sexes of free-living adult females and subadult males are difficult to distinguish except urogenital region is seen.
Killer whales pigmentation make them easily identifiable on the field. They are dark, usually jet black, dorsally with a well-demarked white venter. The white region typically extends from the entire lower jaw posteriorly, constricting medially between the flippers, then widening slightly and ending just beyond the urogenital region. Continuous with the ventral white area is a lateral flank patch (Mitchell, 1970) that expands dorsoposteriorly above the urogenital region. The ventral side of the flukes are white or light gray. There is a postocular white patch. Light-colored areas often are yellowish, especially in animals from the Antarctic (Berzin and Vladimirov, 1982, 1983; Evans et al., 1982), but yellowish coloration also has been reported from the North Pacific (Scammon, 1874; Scheffer and Slipp, 1948); juveniles are more yellowish than adults. A gray or white saddle highly variable in its shape is usually present posterior to the dorsal fin.
Melanistic individuals (Scammon, 1874; Scheffer and Slipp, 1948) and
partially albinistic animals (Carl, 1960; Scheffer
and Slipp, 1948, Cousteau, date?) have been seen in the North Pacific. Individual
and geographical variation in the pigmentation pattern exists (Carl, 1946; Evans
et al., 1982).
Killer whales have been observed in all
oceans and seas of the world (Leatherwood and Dahlheim, 1978). Although
reported from tropical waters and the open ocean, they seem to be most abundant
in colder waters of both hemispheres, with the greatest abundance within
800 km of major continents (Dahlheim, 1981; Mitchell, 1975). Killer whales
inhabiting coastal areas often enter shallow bays, estuaries, and river mouths
(Leatherwood et al., 1976). In some areas they occur seasonally, but in
other areas they are apparently year-round residents (e.g. northeastern Pacific).
In the northeastern Pacific Ocean, killer whales occur in the eastern Bering Sea (Braham and Dahlheim, 1982) and have been documented as far north as the Chukchi and Beaufort seas. Animals seem to be abundant off the coast of Alaska with a population estimate of 286 for the Prince William Sound and southeast waters (Leatherwood et al., 1984). Year-round occurrence has been documented for the intracoastal waterways of British Columbia and Washington State where an estimated 260 whales comprising 30 pods have been reported (Bigg, 1982). In the western North Pacific, killer whales occur frequently along the Soviet coast in the Bering Sea, Sea of Okhotsk (Tomilin, 1957), and off Japan (Kasuya, 1971). Sightings near Hawaii are uncommon (Richards, 1952). Population estimates are not available for the remainder of the North Pacific.
In the North Atlantic Ocean, killer whales have been observed off Greenland, Iceland, in the Barents and White seas, and off Novaya Zemlya (Tomilin, 1957). Regular occurrence also is documented off Norway (Jonsgård and Lyshoel, 1970), Great Britain, and Ireland (Fraser, 1974; Harmer, 1927). Reports from the Mediterranean are sporadic (Casinos and Vericad, 1976). In the western North Atlantic, sightings have been noted in the Labrador Sea, and off Nova Scotia, Newfoundland, Canada (Sergeant and Fisher, 1957). Sightings decrease southward along the continental United States (True, 1904). Several sightings of killer whales have been reported from Caribbean waters (Caldwell et al., 1971). There are no population estimates for the North Atlantic.
In the southern oceans, killer whales occur to the tip of Tierra
del Fuego, South America (Goodall, 1978) and off South Africa
(Ross, 1984), but reports decrease northward along the coasts of both continents.
They occur at wide intervals in the Indian Ocean. In the South Pacific
Ocean, killer whales are recorded from Australia (Bryden, 1978),
New Zealand (Baker, 1983) and off the Galapagos Islands (Robinson
et al., 1983). In Antarctic waters, they have been recorded as
far south as the Ross Sea (Brown et al., 1974, Tomilin, 1957).
Their presence has been observed along the edge of the pack ice throughout Antarctic
waters (Brown et al., 1974). Despite numerous reports of killer whales
in the Southern Hemisphere, details of their distribution, movements, and abundance
are not known (Dahlheim, 1981).
The stratum granulosum and stratum lucidum layers and true keratinization lack in the structure of the epidermis of killer whales, as in several other delphinids (Harrison and Thurley, 1974). Because the epidermis is sloughed rapidly during swimming, the mitotic division rate is rapid and is 290 times that of epidermis from the human forearm (Harrison and Thurley, 1974). On average (n = 7) adult orcas hold 3.6 vestigial facial vibrissae on the right side and 3.7 on the left (Ling, 1977).
Skeletal system of cetaceans in general (Adapted from Green, 1972)
Even to the untrained eye, the cetacean skull appears quite modified in comparison to other mammals. The external nares have migrated posteriorly to lie above the internal nares. The proximal ethmoid is exposed from above, and the palatine forms a part of the narial wall. The rostrum is most often developed into a slender beak.
The maxillae form the major part of the beak and are divided into superior facial and inferior palatine parts by the tooth row. The frontal process of the maxilla is a thin layer of bone spread over the anterior frontal bone and covering most of the lacrimal, reaching the nasal bones and external nares on its medial edge.
The premaxillae are elongated bones fitting between the maxillae and extending posteriorly along the length of the snout to bound the external nares laterally. Ventrally, the premaxillae appear as strips of bone on either side of the midline of the snout, extending posteriorly about one-half the length of the snout. The nasal septum, which is attached posteriorly to the mesethmoid crest and the superior edge of the vomer, extends forward between the median faces of the premaxillae.
The parietal bones fit between the frontal, the supraoccipital, the squamosal, and the lateral margin of the alisphenoid. They are curved ventrally, helping to form the cranial floor lateral to the alisphenoid. The interparietal is an irregular-shaped bone situated between the frontals, the parietals, and the exoccipital.
The frontal bone forms the greater part of the roof and anterior wall of the cranial vault. Except for the stout supraoccipital process, which forms most of the roof of the orbital fossa, this bone is generally thin. The anterior edges of the bone extend under the frontal process of the maxillae. Posteriorly, the bone makes contact with the parietals and interparietals. lnferiorly, it sutures with the outer margin of the alisphenoid.
The malar (zygomatic) bones can best be visualized in the ventral view where they are situated beneath the anterior lateral edge of the frontal process of the maxillae in front of the frontal bones. Each forms part of the pterygopalatine fossa and the anterior part of the orbital fossa.
The vomer is a flat plate of bone attached posteriorly to the ventral. surface of the basisphenoid and anteriorly to the interpalatine suture. The palatines are situated along the midline just anterior to the pterygoids.
The tympanoperiotic (ear capsule) bones vary considerably in their attachment to the cranium. In the Delphinidae, the periotic part of the mastoid is neither wedged into, nor integrated with, the squamosal, and the periotic is separated from the bones of the cranium by an appreciable gap (Purves, 1966).
The hyoid is well developed, appearing as a pair of U-shaped arcs of bone and cartilage passing below and slightly anterior to the larynx. The most posterior are is formed of basihyal and thyrohyal segmeints. The anterior are is formed of cartilaginous ceratohyals which connect the basihyals to well ossified rod-like stylohyals. The stylohyals attach to the cranium by cranium by cartilaginous ceratohyals which connect the basihyals to well ossified rod-like stylohyals. The stylohyals attach to the cranium by cartilaginous tips. These tips may be separate elements and are sometimes called tympanohyals (Lawrence and Schevill, 1965).
The neck is generally shortened with varying degrees of fusion of the cervical vertebrae. In some species (rorquals, narwhals, white whales and river dolphins) all seven bones remain unfused. In other species (right whales and bottlenosed whales) all the bones fuse to form a single osseous unit.
The remainder of the vertebral column is modified by extension, especially in the lumbar area. The total number of vertebrae is quite variable, with the more recent types having the greater number (Slijper, 1962). The caudal vertebrae have well-formed haemal arches (chevron bones), each of which articulates with two vertebral bodies. In addition to forming the haemal arch, the chevron bones also provide a greater surface area for attachment of caudal muscles.
The pectoral girdle is made up of left and right scapular bones and the median sternum. The scapulae are broad, flattened, fan-shaped bones. The structure of the sternum, the number of ribs that attach to it, and the number of double-headed ribs varies among species. In general, the thorax and pectoral girdle are structured with enough flexibility that the thorax can collapse considerably during a deep dive (Ridgway et al. 1969).
The forelimbs or flippers have the same basic structure as the pectoral appendages of other mammals but have developed into flat, fin-shaped paddles. The humerus, radius, and ulna have become so shortened that the elbow is located at the body surface (Felts and Spurrell, 1965, 1966).
The humerus has a large globular head where it attaches to the scapula, while the distal end is flattened where it joins the ulna and radius. The carpals are identifiable as separate bones, while the metacarpals are not identifiable from the proximal phalanges, especially in the three middle digits. While Tursiops has the usual five digits, some of the cetaceans have a reduction from the basic plan.
The pelvic girdle is highly reduced and only the remnants of a pubic bone remain. This short, rod-like bone is embedded in the lateral body musculature, oriented in a longitudinal direction. The bones do not attach to the vertebral column and are generally larger in the male than in the female, serving as an attachment for genital muscles.
Orca skeleton data
The vertebral formula is reportedly:
7 C, 11 to 13 T, 10 to 12 L, and 20 to 24 Ca, total 50 to 54 (Eschricht, 1866; Nishiwaki, 1972).
There are 11 to 13 ribs per side (Eschricht, 1866) with the first six or seven having both capitular and tubercular attachments to the vertebrae and the following attached only by the tuberculum. Ribs 1 through 6 are directly attached to the sternum.
Eschricht (1866) reported the phalangeal formula as:
I 1, II 4 to 6, III 3 to 4, IV 2 to 3, and V 2,
whereas Nishiwaki (1972) reported it as:
I 2, II 7, III 5, IV 4, and V 3.
Nishiwaki's (1972) higher counts may include the morphologically similar metacarpals as the proximal phalanx of each digit. Ends of phalanges and most carpal elements were composed of cartilage in an adult male examined by Eschricht (1866). Harmer (1927) hypothesized that the accelerated secondary growth of the flippers in maturing males was related to the continued growth of these cartilages.
Ness (1967) stated that the degree of skull asymmetry in orcas is low compared with that of other large delphinids. The teeth are relatively large, up to 13 cm in length (Nishiwaki, 1972) and their apices curve inward. Both the mandibular and maxillary aveoli are deep. The teeth are oval in cross-section at the base. Older animals can have extensive wear on the teeth (Caldwell and Brown, 1964). Upper and lower teeth interlock as the jaw is closed.
The entire skeleton is basically built on the typical delphinid plan, but is more robust in all aspects. On the skull, the temporal fossa in noticeably large, indicating a large and powerful temporalis muscle for jaw closure.
A 521-cm (curvilinear) killer whale had 4,500-g brain (Caldwell and Brown, 1964). According to Ridgway and Brownson (1984) the brains mass of 555-cm long killer whales are estimated to weight 5,617 ± 968 g on average. An encephalization quotient of 2.9 has been estimated (Ridgway and Brownson, 1984; Wood and Evans, 1980). This is relatively low for odontocetes, but Wood and Evans (1980) believe this low number may be biased because of the large size of killer whales and their high body weight (caused by blubber).
Digestive system (Adapted from Green, 1972)
The digestive system of killer whales is similar to that of other delphinids.
Most odontocetes have numerous peg-shaped, single-rooted teeth which are generally much alike (homodont). Since these teeth are modified for holding and not for chewing, the jaw musculature is considered weak when compared to that of other mammals. The lower jaw is attached in such a way as to move only in one plane, and the coronoid process is either highly reduced or completely missing.
The odontocete tongue is short and robust with a freely movable tip. Even though whales are usually considered to have little or no gustatory sense, Slijper (1962) reports that taste buds have been described in some species.
The mouth cavity is generally long and narrow anteriorly, widening posteriorly to pass into the highly muscular pharynx. Posteriorly, the pharynx passes into the oesophagus which passes through the thoracic cavity and the diaphragm before entering the first of three main compartments of the stomach.
This compartment, called the forestomach, is non-glandular and is lined with white and yellow non-cornified squamous epithelium. This chamber is formed as a sacculation of the oesophagus.
The second compartment, the main stomach, has a softer velvety lining and is considered homologous to the fundic stomach of other mammals. This is where HCl and pepsinogen are secreted.
The next stomach cavity, the pyloric or connecting stomach, also has a velvety lining but is more tubular than saccular in form in most species. There is some enzyme secretion into this part of the stomach.
The pyloric stomach passes to the duodenum which also has a large dilation just beyond the pyloric sphincter. This chamber, called the duodenal ampulla, is often mistaken for a compartment of the stomach.
The large common bile duct and pancreatic duct drain into the duodenal ampulla.
The intestines are quite long. The measured intestines of one killer whale were 54.2 m long (Eschricht, 1866). The tongue of killer whales is protrusible in contrast to that of bottlenose dolphins (Donaldson, 1977).
In Odontoceti there is no caecum and no gross delineation into small and large intestines.
The liver is generally bilobed and may weigh as much as one ton in larger species of baleen whales. There is no gall bladder, and the hepatic ducts are well developed. The pancreas is generally mammal-like, having from one to several ducts leading from it.
Cave (1977) found that the reniculi of the kidney in orcas are arranged in contiguous groups of four. The venous return from the kidney differs from that of Hyperoodon as the renicular vein receives directly the intrarenicular and centripetal tributaries and no peripheral venous plexus is formed.
Mead (1975) found that, in general, killer whales facial anatomy differed little from the typical delphinid plan of asymmetrical nasal sacs except that several structures were proportionately smaller in comparison to 14 other species.
The amino acid sequence of the myoglobin of killer whales is more similar to that of Globicephala sp. (i.e. pilot whales) than to the myoglobin of other small delphinids and phocoenids examined (Meuth et al., 1981).
Reproductive organs and mammary glands (Adapted from Webster's Whales and Dolphins, 1998.)
Over the course of evolution, the cetacean's body has become streamlined to allow efficient movement in water. As a result, most of their external anatomies have reduced in size, internalized, or been lost altogether. Not surprisingly, the cetacean's genitals and mammary glands have also physically modified over time, almost entirely recessing into the internal body tissues.
The male's penis, when not erect, hides folded in a "S" shape in the abdomen with its tip within a prepucial slit, while the female's mammary glands, one either side of the genital slit, are also internalized when she is not suckling.
The hidden nature of the cetacean's genitalia makes it difficult to distinguish the difference between males and females. The only way to determine the sex of most cetacean is by observing the distance between the genital and anal slits. In females they are close together, often appearing as a single slit. In males, they clearly appear as two separate openings.
Some cetacean species exhibit sexual dimorphism in adulthood. In killer whales, males has a taller, straighter, and more conspicuous dorsal fin than the female. Generally, however, there is no difference in color pattern, or overall difference in body shape, between the sexes.
One captive animal presented an electrocardiogram with no P wave, an inverted T wave, and a simple R wave, the breathing heart rate was 60 beats/min at the surface and declined to 30 beats/min when submerged (Spencer et al., 1967).
The O2 capacity of the blood is reported to be moderate for cetaceans in comparison with the much greater O2 capacity of Kogia blood (Lenfant, 1969).
Human and bovine antibodies cross-react with similar pituitary hormones of killer whales indicating the presence of both lactotrophs and somatotrophs (Schneyer and Odell, 1984).
There is a heat gradient throughout the blubber to the skin. Cetaceans circulatory system adjusts to conserve or dissipate body heat and maintain body temperature. Arteries in the flippers, flukes, and dorsal fin are surrounded by veins. Thus, some heat from the blood traveling through the arteries is transferred to the venous blood rather than the environment.
This countercurrent heat exchange aids whales in conserving body heat. When they dive, blood is shunted away from the surface. This decrease in circulation conserves body heat. During prolonged exercise or in warm water whales may need to dissipate body heat. In this case, circulation increases to veins near the surface of the flippers, flukes, and dorsal fin, and decreases to veins returning blood to the body core. Excess heat is shed to the external environment.
The cetaceans' fusiform body shape and reduced limb size decreases the amount of surface area exposed to the external environment. This helps them conserve body heat. (Sea World Inc., 1993)
Echolocation (Adapted from Webster's Whales and Dolphins, 1998.)
Echolocation, or sonar (SOund NAvigation and Ranging), is the production of sound in the form of short, broad spectrum burst pulses, or clicks, and the reflection of those sounds off surrounding objects.
Sounds are produced by the nasal sacs, focused with the melon. Sounds reflected by the environment (bottom, rocks, congeners or preys) are mainly received with the lawer jaw, and conducted to the inner ear. Then they are coded to be sent to the brain throught the auditory nerve.
Toothed whales (dolphins, porpoises, sperm whales, etc.) including killer whales use echolocation to create with reflected sounds analysed by the brain a three dimensional "sonic picture" of their environment. The ability of dolphins to use echolocation to detect shape and size differences of objects is remarkable.
Dolphins use this amazingly accurate sound system to detect food sources. Their ability to detect minute size differences enables them to estimate the size of fish they are chasing. They also learn to recognize particular species of fish by their behavior, and by the characteristic echoes rebounding off the fish swimbladders. Coupled with sensitive directional hearing, echolocation has given toothed whales a highly sophisticated sensory mechanism for survival in the water.
Ontogeny and reproduction
Breeding cycles seem not to be fixed worldwide with mating and calving seasons often spanning several months. In the northeast Atlantic, mating occurs from late autumn to midwinter (Jonsgård and Lyshoel, 1970). Polygamy undoubtedly exists in killer whales, and there may be some social control of reproduction.
The average size of males at sexual maturity ranges from 5.2 to 6.2 m. An adolescent growth spurt is reported in males from 5.5 to 6.1 m, the time of sexual maturity (Christensen, 1984). Before this, the growth curves from males and females are identical. Harrison et al. (1972) determined from histological examination that a 656-cm individual with testes masses of 3,632 g (right testis) and 2,270 g (left testis) was not mature, and a 724-cm animal with 11,400 g (right testis) and 12,200 g (left testis) testes was sexually mature. An examination of 57 mature males from the Antarctic indicated an average testis length of 55 cm and a width of 22 cm. The average testis mass was calculated at 10,000 g with a maximum mass of 23,100 g (Mikhalev et al., 1981).
Females become sexually mature between a length of 4.6 to 5.4 m (Perrin and Reilly, 1984). Some of this variation is geographic with northeastern Atlantic animals representing the low end and Antarctic animals the high end (Perrin and Reilly, 1984). The size of ovaries from mature killer whales are about 10 to 12 cm by 5 to 7 cm (Mikhaley et al., 1981). A female with a 91-cm fetus had a corpus luteum measuring 7.6 by 5.1 cm (Turner, 1872). A progesterone level of 0.2 to 0.4 ng/mL has been recorded for one female (Kirby and Ridgway, 1984).
Courtship and mating (Adapted from Webster's Whales and Dolphins, 1998.)
Courtship displays and mating in cetaceans are not always directed towards reproduction. Instead, they may simply be a way for animals to greet and bond with one another, or educate. Chasing, nuzzling, rubbing ... even erection and intromission, have been seen in sexually immature males.
The sense of smell is used extensively in sexual encounters in other mammalian species. Cetaceans, however, are thought to lack this sense, so instead use behavioral means to determine the sexual status of potential mates. Some sexual activities in killer whales may also be used by males to ward off competitors.
While mating a male generally turns belly up under a willing female with its penis erect. A short intromission occur when the male has found the female's genital groove with its very mobile and sensitive penis.
Calving intervals and pregnation
Estimates of annual pregnancy rates range from 13.7 to 39.2% with the lower estimates probably more reliable; estimates of annual birth rate range from 4 to 5% (Dahlheim, 1981). Estimates of calving intervals range from 3 to 8 years with observational data indicating that the higher estimates are more typical. However, some evidence suggests that the birth rate may be density dependent (Fowler, 1984; Kasuya and Marsh, 1984). The only killer whales to breed in captivity produced calves 19 months apart (Hoyt, 1981). Estimates of the gestation period in the wild differ from the period observed in captivity with 15 months the best current estimate (Perrin and Reilly, 1984).
Sex ratios at birth appear to be 1:1, but overall ratio of males to females has been reported at 0.48:1 and 0.83:1 for the northeast Pacific (Balcomb et al., 1982; Bigg, 1982), and 1.34:1 for the Marion Islands (Condy et al., 1978).
Detailed embryology and placenta morphology of killer whales has been described for several fetuses (Guldberg and Nansen, 1894; Turner, 1872). The maximum size of fetuses differs regionally and has been documented as 255 cm for the North Atlantic (Perrin and Reilly, 1984), 274 cm for the North Pacific (Nishiwaki and Handa, 1958), and 250 cm for the Antarctic (Mikhalev et al., 1981). The smallest neonates recorded are 183 cm for the North Atlantic, 228 cm for the North Pacific (Perrin and Reilly, 1984), and 227 cm for the Southern Hemisphere (Ross, 1984).
Suckling and weaning
Like other mammals, young cetaceans rely on their mother's milk for the first few months of life. Unlike other mammals, however, the cetacean calf might suck milk from its mother. In any case the mother squirts the milk into her baby's mouth, which is wrapped closely around the nipple with the tongue rolled in a tube around the slightly protruded nipple. This prevents milk from escaping into the water, and being wasted. (Adapted from Webster's Whales and Dolphins, 1998; McBain, pers. comm., 1999)
Lactation is thought to last 12 months (Bryden, 1972). However, calves may suckle for at least 2 years beside eating fish.
Swimming and diving
Norris and Prescott (1961) stated that, in general, killer whales took 3 to 5 short dives of 10-35 sec duration followed by a longer dive lasting 1-4 min. Erickson (1978), summarizing data collected from two radio-tagged transient killer whales, reported a mean dive cycle of 5.77 min. The cycle consisted of a long dive followed by three or four surface blows of 3-4 sec spaced a mean 21 sec apart. The longest recorded dive was 17 min.
Baird and Goodyear (1993), using recoverable time-depth recorders and VHF radio tags, obtained records of 737 consecutive dive profiles for killer whales off Vancouver Island, British Columbia. The maximum depth of dive was 173 m (bottom depth). Velocity during descents and ascents reached 6 m/sec. The maximum recorded depth of dive of a trained killer whale was 260 m (Bowers and Henderson, 1972).
Swimming speeds usually are 6-10 km/hr with a maximum of 40 km/hr (Lang, 1966).
Aerial and other behaviour
Behaviour such as breaching, spyhopping, flipper slapping, and lobtailing is common (Jacobsen, 1986). The significance of such behaviour is not known, and occurrence is within various behavioural contexts. Play behaviour is well documented in killer whales (Osborne et al., 1988). In British Columbia (Hoyt, 1990) and Prince William Sound, Alaska (National Marine Mammal Laboratory, unpublished data), killer whales have been documented to rub along the gravel beds of shallow-water beaches.
Killer whales have an extensive repertoire of sounds covering a wide range of frequencies (Dahlheim and Awbrey, 1982). A series of sacs off the nasal passageway is believed to be involved in sound production (Mead, 975; Heyning, 1989).
Ford and Fisher (1982), working with free-ranging killer whales, documented dialectal variations in the signals among killer whale pods off British Columbia. The extent of vocal differences may reflect the degree of associations among pods (Ford and Fisher, 1983) and the differences have been used to help determine genealogics.
Regional differences in frequency, structure, timing, and call patterns of killer whale sounds have been noted in the Antarctic (Thomas et al., 1981), North Atlantic (Jehl et al., 1980), and the North Pacific (Awbrey et al., 1982). Ford (1989) analysed vocalizations for each of five activity states, including foraging, travelling, group-resting, socializing, and beach-rubbing. High rates of vocal activity occurred during all behavioural categories except group-resting.
Killer whale auditive sensitivity ranges from 500 Hz to 120 kHz, with greatest sensitivity at 15-20 kHz (Hall and Johnson, 1972; Bain et al., in prep.).
Ford and Hubbard-Morton (1990) noted that transient whales typically forage in silence, probably to avoid detection by their marine mammal prey, but calls are usually given during or following a kill.
Northeastern Pacific killer whales
Two forms of killer whales, the "resident" form and "transient" form, have been distinguished British Columbia and Washington State (Bigg, 1982; Bigg et al., 1990). While many researchers currently recognize that the terms resident and transient whales are somewhat misleading in their descriptions, the terms are still so entrenched in the popular and scientific literature that they continue to be used.
The two sympatric (living in the same area) forms are believed to differ in several aspects of morphology, ecology, and behaviour. However, much of what we know about the resident and transient form and/or behaviour of killer whales is derived from research conducted in the northeastern Pacific and then extrapolated to other areas.
It is possible that killer whales occupying other geographical regions or habitats (e.g., offshore environments) may behave and/or segregate differently. Bigg et al. (1987), based on observational data only, noted that the dorsal fin of resident whales tended to be more rounded than those of transient whales. Baird and Stacey (1988) documented differences in saddle patch pigmentation. Bigg et al. (1987) stated that resident pods range in size from 5 to 50 individuals and transient pods range from 1 to 7.
Resident pods are believed to have smaller home ranges than transient whales; however, little is known regarding killer whale winter range and distribution.
Differences have been also noted in the vocalization patterns between the two forms (Ford, 1989; Ford and Hubbard-Morton, 1990).
Northeastern Pacific resident killer whales are mainly piscivorous and rarely prey on marine mammals.
Transient whales frequently are seen pursuing marine mammal prey, but there are cases of transient whales eating both fish and marine mammals in southeastern Alaska (M. Dahlheim, personal observations) and Prince William Sound, Alaska (Matkin and Saulitis, 1994).
Studies on mDNA restriction patterns provide evidence that the resident and transient pods are genetically distinct (Stevens et al., 1989; Hoelzel, 1991a; Hoelzel and Dover, 1991).
Killer whales usually occur in small pods, with typically fewer than 40 individuals. Large groups may reflect the temporary merging of a number of pods, possibly related to seasonal peaks in prey availability or reproductive activities. Single whales, usually adult males, occur infrequently (Norris and Prescott, 1961).
Bigg et al. (1990) examined the social organization and genealogy of resident killer whales in the coastal waters of British Columbia and Washington State. The authors classified the social organization into communities, pods, subpods, and matrilineal groups. They defined these terms as follows:
Matrilineal groups are the basic unit of social organization, and consist of whales from 2-3 generations.
Occasionally, when resident pods encounter each other after being separated for some time, the pods will form two tight lines and approach each other head on. When the groups are within 10-20 m of each other, they stop motionless at the surface and hover, facing each other for 10-30 sec (Osborne, 1986). Intermingling typically follows this greeting ceremony. Intermingling is characterized by slow moving and tight milling concentrations of whales. Many of the whales are in physical contact, rolling and brushing against each other at or near the surface.
Parallel scars caused by the tooth marks of other killer whales indicate that some intraspecific aggression occurs (Greenwood et al., 1974). However, parallel scars could be obtained during other social activities. Many scratches or rake marks may also be the result of interactions with pinnipeds during predation events (M. Dahlheim, personal observations).
Care-giving is well documented (Caldwell and Caldwell, 1966). Waite (1988) describes alloparental care in killer whales. Adolescent females performed most of the alloparenting, although non-reproductive females and males were also observed to alloparent. Adult bulls have been observed to "baby-sit" groups of calves and juveniles (Osborne et al., 1988).
Although regular sightings and recurrence of the same pods have been documented within specific areas, territoriality among pods has not been documented.
Transient whales appear to cover a more extensive range than residents. A distance of over 2600 km (California to Alaska) has been reported for a transient group (Goley and Straley, 1994).
Killer whales are marine carnivores at the end of the food chain. Their diets differ seasonally and regionally. Killer whales are known to have a variety of prey, including fish, other cetaceans, pinnipeds, mustelids, birds, reptiles, and cephalopods.
Main components of the diet of killer whales around the world:
|Norwegian waters||mainly herring||Jonsgård and Lyshoel, 1970|
|Japanese waters||mainly cod, flatfish, and cephalopods||Nishiwaki and Handa, 1958|
mainly fish in resident killer whales;
|Bigg et al., 1987; Ellis et al., 1987|
|Puget Sound||mainly salmon in resident killer whales||Balcomb et al., 1979|
mainly marine mammals in "white" killer whales;
|Berzin and Vladimirov, 1983|
|Argentina||mainly elephant seals and sea lions||Lopez and Lopez, 1985|
Most food items are swallowed whole. However, when whales attack larger prey, they rip away smaller pieces of flesh and then consume them. The tongues, lips, and genital regions of baleen whales seem to be the favoured parts.
In most geographical regions, killer whale movements may be related to movements of their prey (Sergeant and Fisher, 1957; Jonsgård and Lyshoel, 1970). Whales may travel 125-200 km per day while foraging.
The daily food intake is unknown, though Mitchell (1975) estimated that killer whales consume 4% of their body weight per day.
Killer whales consume fish of commercial importance. Troll catches of salmon show a decline when killer whales are in the area (Pike and MacAskie, 1969) and damage to fishing gear has also been reported (Scheffer and Slipp, 1948; Nishiwaki and Handa, 1958).
When hunting pinnipeds, killer whales use a variety of strategies, probably dependent upon the prey species being targeted. The particular hunting or feeding strategy, or target prey, probably dictates the concentration and dispersal of killer whales (Dahlheim and Heyning, 1999).
An updated review of hunting techniques described in killer whales (Orcinus orca) around the world.
Diagram of the level of cooperation within and between groups, in accordance with prey size and in relation to acoustic behavior.
Although there are no documented instances of killer whales eating man, a few unsuccessful attacks have been reported (di Sciara, 1978).
The following life history parameters are based on the changes observed in the northern and southern resident communities in the coastal waters of British Comlumbia and Washington State. Females mean life expectancy is 50.2 years. They give birth to thier first viable calf at 14.9 years, and produce an average of 5.35 viable calves over a 25.2 year reproductive lifespan. Their maximum longevity is about 80-90 years. Neonate mortality is approximately 43%. Males have a mean life expectancy of 29.2 years. They typically attain sexual maturity at 15 years and physical maturity at 21 years of age. Their maximum longevity is about 50-60 years. (Olesiuk, Bigg and Ellis, 1990) The natural mortality rate of killer whales is not known, but may be approximately 5% per year for the total population based on information concerning life spans.
The age of most odontocetes is determined by sectioning teeth and counting the dentine or cementum layers. Distinct layering of dentine is present in tooth sections from killer whales, but numerous accessory layers make them difficult to interpret (Perrin and Myrick, 1980). The relationship of dentine layers to absolute time for orcas is unknown at present.
The following endoparasites are known from the species : Trematoda, Fasciola skriabini; Cestoda, Trigonocotyle spasskyi, Phyllobothrium sp.; and Nematoda, Anasakis simplex (Dailey and Brownell, 1972).
Killer whales are relatively free of external parasites but barnacles (Xenobalanus and unidentified) have been observed on the rostrum and trailing edge of the flukes (Los Angeles City Museum No. 72550). There are photographs of a remora (Echeneididae) attached to a killer whale (Lockyer, 1979). Diatoms were reported on the skin of Antarctic animals (Hart, 1935). The ectoparasite Cyamus orcini has been described from killer whales (Leung, 1970).
The most common disease reported for killer whales is caused by the wearing of teeth resulting in exposure of the pulp cavity. Infection may penetrate through the pulp cavity causing a jaw abscess. Simpson and Gardner (1972) reported frequent abscessed follicles of the vestigial hair on the rostrum of captive animals that eventually spread over the entire skin surface. The cause of death for captive killer whales (n = 32) was reported by Greenwood and Taylor (1985) as pneumonia (25%), systemic mycosis (22%), other bacterial infections (15.6%), mediastinal abscess (9.4%), and undiagnosed (28%). Atherosclerosis was found in one stranded animal (Roberts et al., 1965). The rare genetic Chidiak-Higashi syndrome has been documented in a captive killer whale (Haley, 1973).
Effects of environmental pollutants are not known for cetaceans, however, Calambokidis et al. (1984) found high levels of PCBs and DDT in the tissues of killer whales from Washington State waters.
Killer whales have no significant predators other than man. In various parts of the world, killer whales have been hunted for oil and meat, or killed as a potential competitor by fishermen (Dahlheim, 1981). Tomilin (1957) listed the oil yield for killer whales as between 750 and 950 kg per animal and Eschricht (1866) noted that 205 L was yielded from a 6.4-m animal. Killer whale oil in Japan is equal in price to sperm whale (Physeter catodon) oil. Killer whale oil has an acid value of 0.63, saponification value of 211.9, and an iodine value of 86.4 (Nishiwaki and Handa, 1958). The fresh meat of killer whales is used for human consumption in Japan, but old meat and viscera are used as fertilizer or bait (Nishiwaki and Handa, 1958). In Norway, orcas meat is used only for animal consumption (Jonsgård and Lyshoel, 1970).
From 1962 to 1976, a live-capture fishery was active in Washington State and British Columbia. By 1976, 302 animals were captured, of which 10 died, 55 were kept for public display in oceanaria, and 237 were released (Asper and Cornell, 1977). Bigg and Wolman (1975) provided data on the live-capture fishery in this area from 1962 to 1973 with slightly different numbers. Since 1976, only one live killer whale was captured in this region. Beginning in 1976, Iceland became active in the live-capture fishery (Greenwood and Taylor, 1985).
Please, cf. Under construction bibliography.
© 1997-2000 Eric
PONCELET & original authors,
Killer whale (Orcinus orca) biology.