Sperm Whales (Physeteridae)
Small to large whales, with distinctive, barrel-shaped heads, blowholes left of center, narrow, underslung lower jaws with uniform teeth, and paddle-shaped flippers
Number of genera, species
2 genera; 3 species
Vulnerable: 1 species
Worldwide in tropical and temperate waters reaching latitudes of about 40°; mature male sperm whales up to edges of pack ice
Evolution and systematics
The family Physeteridae is about 30 million years old and among the oldest of living families of whales and dolphins. They are thought to have separated quite early from the main odontocete (toothed whale) line, and retain many of the characteristics that are considered primitive in odontocetes. Some of their features are highly derived, however. There is little similarity to the primitive Eocene cetaceans from which they descended.
The earliest physeterid (Ferecetotherium), appearing in the late Oligocene, was small with a reduced head size. It represents the earliest record of a living odontocete family. By the middle of the Miocene, the physeterids were fairly diverse, and the family is moderately well documented in the fossil record. The sperm whale (Physeter macrocephalus) is the only surviving species of the genus (Physeter) and is the most phylogenetically distinct of all the species of living odontocete. The pygmy and dwarf sperm whales (Kogia species) are often placed in a separate family, Kogiidae, as they emerged much later, about 7 million years ago in the late Miocene.
All three species are characterized by a highly asymmetrical rostrum, but Kogia has a lesser developed melon (fat-filled forehead), which makes up a much smaller proportion of their body length than in the sperm whale. The blowhole is also more posterior, the head more conical, and the rostrum is shorter in Kogia (indeed, this genus has the shortest rostrum of all the living cetaceans). At least two structures contained within the forehead are unique to the Physeteridae: the spermaceti organ and the museau de singe. The spermaceti organ is an elongated structure made up of spongy tissue containing a liquid or semi-liquid waxy oil, and the museau de singe is a valve-like clapper system that lies at the end of the right nasal passage. Both are believed to be involved in sound production. The right nasal passage is much smaller than the left; the former is thought to be used for sound production, and the latter, for respiration.
Members of this family are dark gray in color, with a lighter-colored belly. None of the three species has teeth in their upper jaw, though small, unerupted teeth (around 10 on each side of the sperm whale jaw) remain in the upper jaw during their lifetime. The teeth of the lower jaw all erupt around the time of sexual maturity. The sperm whale has 17–29 teeth on each side of its lower jaw; the pygmy sperm whale, 12–16; and the dwarf sperm whale, eight to 11. Physeter teeth are large and conical. In contrast, the teeth of Kogia are thin, very sharp and curved, and lack enamel.
The sperm whale is the largest odontocete and the most sexually dimorphic one. Adult females are about 36 ft (11 m) in length and weigh 33,000 lb (15,000 kg), but can reach 41 ft (12.5 m) and 53,000 lb (24,000 kg). Physically mature males are roughly 52.5 ft (16 m) long and 100,000 lb (45,000 kg), though maximum sizes are 60 ft (18.3 m) and 125,000 lb (57,000 kg). In the Kogia spp., the sexes are roughly the same size.
The distributions of the Physeteridae family members are cosmopolitan. Few animals in the world have such wide distributions as the sperm whale, occurring in all oceans, from the pack ice to the Equator. The ranges of the pygmy and dwarf sperm whales are perhaps somewhat smaller than that of the sperm whale, but they are found worldwide in warm-temperate and tropical waters of the Atlantic, Pacific, and Indian Oceans. The dwarf sperm whale seems to prefer warmer waters than the pygmy sperm whale. Knowledge of Kogia distributions is sketchy, however, as most records are based on stranded animals.
The Physeteridae occupy mainly deep, oceanic waters over 3,300 ft (1,000 m) in depth, (off the edge of the continental shelf. However, the Kogia spp., particularly the dwarf sperm whale, live in shallower water over the continental shelves and shelf edges.
All three species are known to strand, but the pygmy sperm whale is one of the most commonly stranded cetacean species. Much of what is known of Kogia is based solely on information from strandings. When surfacing for air, all of the Physeteridae produce a low, relatively inconspicuous blow.
Very little is known about the behavior of pygmy or dwarf sperm whales, as there have been no comprehensive behavioral studies. Group sizes in the Kogia spp. range from single individuals to a maximum of six (pygmy sperm whale) or 10 (dwarf sperm whale) animals of varying age and sex composition. Groups of dwarf sperm whales can be composed of adults of both sexes with calves, females with calves, or immatures only. The Kogia spp. rise slowly and deliberately when they are surfacing and dive without showing their flukes. They spend a considerable amount of time lying motionless at the surface, with their tail hanging limply down and the back of their head exposed. The Kogia spp. are reported to have an interesting adaptation, presumably used in predator defense. When startled or distressed, they discharge a quantity of reddish brown intestinal fluid. This may function like octopus ink to confuse predators, enabling their escape. Neither Kogia is known to be highly vocal, though they do use echolocative, directional clicks.
The sperm whale, in contrast, is much more social and vocal than Kogia. Indeed, female sperm whales are exceptionally colonial. Sperm whale society is complex and built around the long-term unit, which is made up of around 10 females and their young. These units are generally matrilineal, but consist of more than one matriline. Most females probably spend their lives in the same unit, surrounded by close female relatives like aunts, cousins, and grandmothers. Two or more units may join together for several days at a time, forming a group of 20–30 animals.
Female sperm whales regularly gather at the surface to socialize or rest for several hours a day, or 25% of their time. Whales can be tightly aggregated, lying quietly and parallel to one another, a behavior called "logging," or they may vigorously twist and turn about one another, often touching one another. Breaches (leaps from the water), lobtails (hitting the water with tail flukes), and spyhops (raising the head vertically out of the water) can also be observed during these social times.
These are also the circumstances in which sperm whales typically are either silent or emit "codas," which is a patterned series of around three to 20 clicks that are somewhat reminiscent of the Morse code. Codas are less than two seconds long and can often be heard as exchanges between individuals; codas clearly represent communication in Physeter. Groups vary in their usage of different coda types, thus exhibiting dialects, and these dialects are stable over time. Moreover, units can be clustered into "vocal clans" based on the similarity of their dialects. Variation in vocal behavior between clans is likely cultural, passed down from mother and clan to offspring.
The most commonly heard sounds from sperm whales, though, are the usual clicks, which are long trains of regularly-spaced clicks, produced at rates of about two clicks per second. These very loud, highly directional clicks most likely represent echolocation used in food-finding behavior. Slow clicks, or clangs, are distinctively ringing clicks produced by large males, generally on the breeding grounds. They are emitted every six seconds or so, and may advertise a breeding male's presence and/or fitness.
Male sperm whales leave their natal units at an age of about six years. They then form bachelor schools, which are loose aggregations of males of about the same size and age. As males grow, they are found in progressively smaller schools, with the largest males being mostly solitary.
Feeding ecology and diet
All of the Physeteridae feed principally on mid- and deep-water squid, although they also eat some fish and octopus. Their anatomy suggests that they use powerful suction feeding. The sperm whale eats mainly deep-ocean squid, 0.2–15.5 lb (0.1–7 kg) in weight, but occasionally, it will prey on giant and jumbo squid, over 50 ft (15 m) in length. Scars from the squids' sucker marks can be found on sperm whales' heads as proof of these undersea battles. Males are more likely to eat fish, but will also feed on larger species and larger individuals of the same species of squid that females eat.
Kogia have an anterior-ventrally flattened snout, which points to a tendency to bottom-feed at least some of the time. Indeed, bottom-dwelling fish and crabs have been found in their stomachs. The Kogia spp. eat some of the same species as the sperm whale, but because they also inhabit the continental shelf region, they feed on shelf-living squids and octopods.
The Physeteridae are deep divers, with the sperm whale being the champion in this department. It can dive to depths
of 3,300–6,500 ft (1,000–2,000 m), possibly even 10,000 ft (3,000 m). More typical are dives to 1,000–2,600 ft (300–800m). Dives are usually 30–45 minutes in length with seven to 10 minutes at the surface between dives to breathe. Dives can last over an hour, however. Females spend about 75% of their time foraging. The pygmy and dwarf sperm whales are also probably capable of diving to greater than 1,600 ft (500 m), judging by the prey they ingest.
In the sperm whale, the sexes show an unusual pattern of distribution, where females and immatures inhabit warmer waters at latitudes below 40° and males are found at higher latitudes. As males mature, they move to higher and higher latitudes, with the largest males found close to the edge of the pack ice. Mature males in their late twenties and older make the long migrations to the tropics to mate. The sperm whale is polygynous. On the breeding grounds, large males rove between groups of females, most likely searching for receptive females. They spend only minutes to hours with each female group. Rare fights occur between mature males.
Very little is known of the mating system of the pygmy or dwarf sperm whales. Little or no sexual dimorphism is apparent in either species, so they may have a different reproductive strategy from the highly sexually dimorphic sperm whale.
Sperm whales give birth about once every five years. Calves can ingest solid food by the age of one year, but continue to suckle for two or more years. This species exhibits one of the longest periods of parental care among marine mammals, as calves can be suckled for as long as 13–15 years. The calves are the probable reason behind female sperm whale sociality. Young calves seem unable to make the prolonged dives to the depths their mothers do to feed. Left alone at the surface, they would be vulnerable to attacks by killer whales or sharks. Thus, calves are "babysat" by other members of the group remaining
at the surface. Groups containing calves stagger their dives, leaving some adults available to stand guard at the surface at all times, while groups without calves dive more synchronously. In addition to this communal care for the young, there is strong evidence for females suckling calves that are not their own.
Gestation is 14–16 months for sperm whales; 11 months for pygmy sperm whales; and nine months for dwarf sperm whales.
All three species are reported to ingest ocean debris such as plastic bags, causing death on occasion. This family is also vulnerable to ship strikes. Population sizes for Kogia are unknown, though they are apparently not common. The global population of sperm whales is very roughly 360,000. The sperm whale is listed as Endangered under the U.S. Endangered Species Act and Vulnerable by the IUCN. All three species are listed on CITES Appendix I or II.
Sperm whales were heavily whaled around the world in the eighteenth and nineteenth centuries, but especially by the New Englanders. In the twentieth century, a second wave of whaling took place, using mechanized catcher vessels and explosive harpoons. Up to 30,000 sperm whales were killed
every year, particularly the large males. Commercial whaling more or less ceased in 1988 with the International Whaling Commission's moratorium.
The sperm whale, with a maximal rate of increase of just 1%, is slow to recover from past whaling. Additional threats include chemical pollution, evident in its blubber, and noise pollution, because of its dependence on sound for all aspects of its life.
Significance to humans
The sperm whale is memorialized in Herman Melville's novel, Moby Dick. Japan has restarted sperm whaling in 2000, taking five to eight sperm whales a year. Whale-watching for sperm whales is a profitable business around the world, bringing in substantial revenue from tourists. Pygmy and dwarf sperm whales are occasionally taken in commercial harpoon fisheries in the Indian and Pacific Oceans, and the Caribbean.
List of SpeciesSperm whale
Pygmy sperm whale
Physeter macrocephalus Linnaeus, 1758, "Oceano Europaeo."
other common names
French: Cachalot; German: Pottwal; Spanish: Cachalote.
Square forehead makes up one quarter to one third the body length. Body dark gray, but mouth has bright, white lining. Skin corrugated, except for head and flukes.
Deep water near productive areas; often near steep drop-offs or strong oceanographic features. Males more likely in shallower waters.
Females highly social, males solitary. Very vocal.
feeding ecology and diet
Eats mainly deep-ocean squid. Dives vertically, raising flukes in air. Females forage in rank abreast of each other.
Polygynous. Breeding season in northern hemisphere, January– August; in southern hemisphere, July–March.
Listed as Vulnerable by the IUCN. In 2002, global population size was about 32% of pre-whaling numbers. Large, breeding males scarce, and calving rates below sustainability in southeast Pacific. Still widespread, however.
significance to humans
In the past, whalers used the valuable oil from the spermaceti organ and blubber to fuel the industrial revolution. Minimal sperm whaling since 2002. Sperm whale-watching operations off New Zealand, West Indies, Norway, Madeira, the Azores, etc.
Pygmy sperm whale
other common names
French: Cachalot pygmée; German: Zwergpottwal; Spanish: Cachalote pigmeo.
Bluish steel gray on back. Shark-like appearance. Bracket-shaped mark on side of head, resembling gill slit.
Worldwide in warm-temperate and tropical waters.
Deep, oceanic waters and over the continental shelf.
Difficult to observe at sea. Easily approached, timid and slow-moving.
feeding ecology and diet
Deep-ocean and shelf-dwelling squid and octopus; fish and crabs.
May give birth two years in succession, i.e., can be pregnant and nursing simultaneously. Calves nurse for about one year. Mating believed to occur in summer, births in spring. Mating system unknown.
Population size unknown, though not common. Not listed by the IUCN.
significance to humans
Sometimes taken in commercial harpoon fisheries.
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Lindy Weilgart, PhD