Sperm whale

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How to read a taxoboxSperm whale
Scarred Giant (detail)—Artist: Chris Harman
Scarred Giant (detail)—Artist: Chris Harman
Size comparison against an average human
Size comparison against an average human
Conservation status
Status iucn3.1 VU.svg
Vulnerable

(IUCN) [1]

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Family: Physeteridae
Genus: Physeter
Species: P. macrocephalus
Binomial name
Physeter macrocephalus
Linnaeus, 1758
Sperm whale range (in blue)
Sperm whale range (in blue)

Sperm whale or cachalot is the common name for a large toothed whale, Physeter macrocephalus (or Physeter catodon), characterized by a enormous squarish head, blunt snout, underslung lower jaw, small and rounded flippers, and low, rounded humps on the back near the rear of the body. The sperm whale is the largest of all toothed whales (suborder Odontoceti) and perhaps the largest toothed mammal ever.

The sperm whale was named after the milky-white waxy substance, spermaceti, found in a cavity in its head and originally mistaken for sperm. The sperm whale's enormous head and distinctive shape, as well as its central role in Herman Melville's novel Moby-Dick, have led many to describe it as the archetypal whale. Partly because of Melville, the sperm whale is commonly associated with the Leviathan of the Bible.

The sperm whale is among the most cosmopolitan species in the world, and is found in all the oceans and the Mediterranean Sea. The species is relatively abundant from Arctic waters to the equator. Populations are more dense close to continental shelves and canyons, probably because of easier feeding. Sperm whales are usually found in deep off-shore waters, but may be seen closer to shore in areas where the continental shelf is small.

With its large size, the sperm whale adds to the wonder of nature for humans, while it also has been important as an historical source of the spermaceti that was much sought after by eighteenth-, nineteenth- and twentieth century whalers. This substance was used for such purposes as watch oil, automatic transmission fluid, cosmetics, additives in motor oils, glycerine, vitamins, and numerous other products. Sperm whales also yield ambergris (from the intestines) that is used in perfumery, as well as for medicinal and flavoring purposes. Ecologically, the sperm whale has been an important predator of squid and fish from the ocean deaths, including giant squid, while young whales and females are a source of food for orcas.

Historically, the sperm whale has also been known as the common cachalot. The word cachalot is originally Portuguese (cachalote), probably coming from cachola, a colloquial term for "head." Sperm whales were hunted until recently in the Portuguese Atlantic archipelago of the Azores.

Contents

Description

Sperm whales are members of the order Cetacea, which also includes dolphins and porpoises. Like all mammals, members of Cetacea breathe air into lungs, are warm-blooded, breast-feed their young, and have hair (although very little). Whales breathe air through blowholes that lead into their lungs. Whales have a unique respiratory system that lets them stay underwater for long periods of time without taking in oxygen. Some whales, such as the sperm whale, can stay underwater for up to two hours holding a single breath.

Cetaceans are divided into two suborders, Mysticeti (baleen whales) and Odontoceti (toothed whales). Sperm whales are members of Odontoceti. As toothed whales, they have teeth and only one blowhole.

The sperm whale is the largest toothed animal alive, with some males reaching 20 meters (66 feet) or more in length. Sperm whales are among the most sexually dimorphic (that is, males and females differ greatly) of all cetaceans. Males are typically 30 to 50 percent longer (16-18 meters or 52–59 feet) than females (12-14 meters or 39–46 feet) and are twice as massive (50,000 kilograms versus 25,000 kilograms, or 55 short tons vs 27.5 short tons). At birth, both males and females are about 4 meters (13 feet) in length and mass of 1,000 kilograms (1 metric ton).

Sperm whales are uniformly dark gray or dark blue-black in color, some with white undersides, but with a bright, white lining to the mouth. The gray color may appear brown in sunlight; white albino whales have also been reported. In contrast to the smooth skin of most other large whales, the skin on the back of the sperm whale is usually knobbly and has been likened to a prune by whale-watching enthusiasts (Carwardine 1994).

The sperm whale is exceptional for its very large head, particularly in males, which is typically one-third of the animal's length. Indeed, the species name macrocephalus is derived from the Greek for "big head." The brain of the sperm whale is the largest and heaviest known of any modern or extinct animal, weighing on average 7 kilograms (15 pounds) in a grown male. However, the brain is not large relative to body size. The blowhole is situated very close to the front of the head and shifted to the whale's left. This gives rise to a distinctive bushy blow angled forward.

The flukes of a sperm whale as it dives into the Gulf of Mexico (courtesy NMFS)

The sperm whale has no true dorsal fin, instead a series of ridges are present on the caudal third of the back. The largest was called the "hump" by whalers and is commonly mistaken for a dorsal fin because of its shape. The fluke is also triangular and very thick. Flukes are lifted very high out of the water before a whale begins a deep dive.

Sperm whales have 20–26 pairs of cone-shaped teeth in their lower jaw, each 8–20 centimeters (3–8 inches) long (ACS 2004). Each tooth can weigh as much as one kilogram. The reason for the existence of the teeth is not known with certainty. It is believed that they are not necessary for feeding on squid and indeed healthy well-fed sperm whales have been found in the wild without teeth. There is speculation that the teeth may be used for aggression between males of the same species, a hypothesis that is consistent with the conic shape and wide spacing of the teeth. Furthermore, bull sperm whales often show scars that seem to be caused by the teeth of other bulls. Rudimentary teeth are also present in the upper jaw, but these rarely open into the mouth.

Owing to extensive whaling, sperm whale size has decreased dramatically, mostly because the largest males were killed first and most intensively, for they had more spermaceti. (Spermaceti oil was of great value in the 18th and 19th century. See below.) In a Nantucket museum, there is a jawbone of a sperm whale that is 5.5 meters (18 feet) long. The jawbone typically makes up to 20 - 25 percent of the sperm whale's overall body length. Thus, this whale might have been 28 meters (90 feet) long, with a mass of around 133 metric tons (150 short tons). Another evidence of large bulls of the past resides in New Bedford museum, a 5.2 meter (17 foot) jaw of a bull that could have been about 25.6 meters (84 feet) long, with a mass of about 120 tons. In addition, log books found in the Nantucket and Bedford museums are filled with references to bulls that were, considering the amount of oil they yielded, about the same size as these two examples. Today, sperm whale males do not usually exceed 18 meters (60 feet) in length and 52 metric tons (57 short tons). The largest sperm whales observed are comparable in size to the fin whale (and smaller than blue whales), making the sperm whale either the second or third largest animal species alive (after these baleen whales).

Sperm whales are a prime example of a species that has been K-selected, a reproductive strategy associated with very stable environmental conditions that is characterized by a low birth rate, significant parental aid to offspring, slow maturation, and high longevity. Females give birth once every four to six years, and the gestation period is at least 12 months and possibly as long as 18 months. Nursing takes place for two to three years. In males, puberty lasts for about ten years between the ages of about 10 and 20. Males continue to grow into their 30s and 40s and only reach their full size when about 50 years old. Sperm whales live for up to 80 years.

The sperm whale holds some natural world records:

  1. Largest known toothed mammal ever. A bull sperm whale was recorded in 1950 as measuring 20.7 meters (67 feet, 11 inches) (4to40.com 2007).
  2. Largest brain of any living creature on Earth. The brain of a mature sperm whale weighs 7 kilograms (15 pounds), though there have been specimens with 9 kilogram (20 pound) brains (GA 2001).
  3. Largest living carnivore on Earth (Martin 2001).
  4. Deepest diving mammal. Sperm whales have been found at depths of 2,200 meters (7,200 feet) and can hold its breath for up to two hours.
  5. Loudest animal in the world. Sperm whale clicks have a source level exceeding 230 dB re 1 micropascal referenced to a distance of 1 meter (Møhl et al. 2003). Trivedi (2003) notes that clicks measuring about 230 decibels underwater are equivalent to 170 decibels on land.

In 1820, a sperm whale estimated to be about 25.9 meters (85 feet) long attacked a Nantucket whaling ship Essex. Only 8 out of the 20 sailors managed to survive and be rescued by other ships.

Spermaceti

Scarred Giant—Artist: Chris Harman

Spermaceti is the semiliquid, waxy substance found in the head of the sperm whale. The name derives from the late Latin sperma ceti (both words actually loaned from Greek) meaning "sperm of the whale" (strictly, "sperm of the sea monster"). The common name for the species is actually an apocopation of Spermaceti Whale. The substance is not, of course, the whale's semen, but it was mistaken for such by early whalers. Spermaceti is found in the spermaceti organ or case in front of and above the skull of the whale and also in the so-called junk, which is right at the front of the whale's head just above the upper jaw. The case consists of a soft white, waxy substance saturated with spermaceti. The junk is a more solid substance.

One function of the spermaceti organs is a buoyancy or diving organ. Before diving, cold water is brought through the organ and the wax is solidified. The increase in specific density generates a down force (approx 40 kilogram equivalent) and allows the whale effortless sinking. During the chase in deep levels (max 3,000m) the stored oxygen is consumed and excess heat melts the spermaceti. Now only hydrodynamic forces (by swimming) keep the whale down before effortlessly surfacing.

Hypotheses on further functions exist. One function incidentally discussed in Moby-Dick by Melville, is that the case evolved as a kind of battering ram for use in fights between males (Carrier et al. 2002). This hypothesis is consistent with the well-documented sinking of the ships Essex and Ann Alexander due to attacks by sperm whales estimated to weigh only one-fifth as much as the ships.

Another possibility is that the case is used as an aid to echolocation. The shape of the organ at any given time is likely to focus or widen the beam of emitted sound (Cranford 2007). The sperm whale actually has two nostrils, one external nostril, forming the blow hole, and one internal nostril pressing against the bag-like spermaceti container. A hypothesis pertaining to the echolocation abilities of these animals holds that the combination of the shape of the whale's skull, the highly variable geometry (in three dimensions) of the muscle-sheathed spermaceti container, and the presence of this "internal nostril" may endow the sperm whale with astounding powers of sound production—not only being able to echolocate with high fidelity, but to produce other effects with sound waves/mechanical energy as well. For example, it is postulated that sperm whales, ungainly and ponderous swimmers, may need "something extra" to capture the agile-swimming squid they eat, and the ability to stun or even kill such prey with a burst of sound would "fit the bill." However, so far, this hypothesis remains only intriguing speculation.

Spermaceti was much sought after by eighteenth-, nineteenth- and twentieth century whalers. The substance found a variety of commercial applications, such as watch oil, automatic transmission fluid, lubricant for photographic lenses and delicate high-altitude instruments, cosmetics, additives in motor oils, glycerine, rust-proofing compounds, detergent, chemical fibers, vitamins, and 70 or more pharmaceutical compounds.

Behavior

A piece of sperm whale skin with giant squid sucker scars

Diving

Odontoceti (toothed whales) breathe air at the surface of the water through a single, s-shaped blowhole. The blowhole is located on the left side of the front of the head. They spout (breathe) 3–5 times per minute at rest, but the rate increases to 6–7 times per minute after a dive. The blow is a noisy, single stream that rises up to 15 meters (50 feet) above the surface of the water and points forward and to the left of the whale at a 45° angle.

Sperm whales, along with bottlenose whales and elephant seals, are the deepest-diving mammals in the world.

Sperm whales are believed to be able to dive up to 3 kilometers (1.9 miles) in depth and 90 minutes in duration to the ocean floor. More typical dives are around 400 meters (437 yards) in depth and 30–45 minutes' duration and generally move in a northerly direction. They can dive two miles deep with one gulp of air for two hours. They carry three ton of blood, which holds enough oxygen to help it achieve its diving depth.

The physiology of the sperm whale has several adaptations to cope with drastic changes in pressure when diving. The ribcage is flexible to allow lung collapse, and the heart rate can decrease to preserve oxygen supplies. Myoglobin stores oxygen in muscle tissue. Blood can be directed towards the brain and other essential organs only, when oxygen levels deplete. The spermaceti organ may also play a role (see above).

Sperm whale jumping at the Azores

While sperm whales are well adapted to diving, repeated dives to great depths do have long term effects on the whales. Skeletons of sperm whales show pitting of the bones that is often a sign of decompression sickness in humans. Skeletons of the oldest whales showed the most extensive pitting, whereas skeletons of sperm whale calves showed no damage. This damage may indicate that sperm whales are susceptible to decompression sickness, and sudden surfacing could be lethal to them (Moore and Early 2004).

Between dives, the sperm whale will come up to the surface for breath and remain more or less still for eight to ten minutes before diving again.

Because of the great depths to which they dive, sperm whales sometimes drown when entangled in transoceanic telephone cables (Southwestern 1986).

Feeding and predators

Sperm whales feed on several species, in particular giant squid, octopus, and diverse fish like demersal rays. However, the main part of their diet consists of medium sized squid. Almost all that is known about deep sea squid has been learned from specimens found in captured sperm whale stomachs.

Giant squid are considered to be part of the sperm whale's main diet, as large deep sea fish stocks are becoming depleted by humans. Titanic battles between sperm whales and colossal squid, which can reach up to 14 meters (46 feet), have never been observed by humans. However, white scars on the bodies of sperm whales are believed to be caused by squid.

It is hypothesized that the sharp beak of a consumed squid lodged in the whale's intestine leads to the production of ambergris, analogous to the production of pearls. The irritation of the intestines caused by the beaks stimulates the secretion of this lubricant-like substance.

Sperm whales are prodigious feeders and eat around 3 percent of their body weight per day. The total annual consumption of prey by sperm whales worldwide is estimated to be about 100 million tons—a figure greater than the total consumption of marine animals by humans each year (Ellis 1994).

Stealing of sablefish and toothfish from long lines has been documented and well known also. It is believed that this trait is learned and passed on to other whales within the pod or offspring. Long-line fishing operations in the Gulf of Alaska have complained that numerous sperm whales have taken advantage of their fishing operations to eat desirable species straight off the line, sparing the whales the need to hunt them themselves. However, the amount of fish taken is very little compared to what the sperm whale needs per day.

The only predator that attacks sperm whales, besides human beings, is the orca (killer whale). Large, roving pods of orcas frequently target groups of females with young, usually trying to separate the sperm whale calf and kill it. Often, the female sperm whales can repel these attacks by forming a circle with their calves in the center and then violently thrashing their tail flukes, so that no orca can penetrate the formation. If the orca pod is extremely large, they may sometimes also kill adult females. Large bull sperm whales have no predators, as even orcas could be killed by these aggressive, powerful creatures.

With such a large head in comparison to the lower jaw, it is difficult to see how the sperm whale could be such a successful hunter. A theory of its success is the inordinate size of the sperm whale's head and its ability to echolocate through it. Within the head, it contains a structure called monkey lips, with which it blows air through. This can create massive sounds, which when directed at a prey can stun them giving the sperm whale an easier meal.

Social structure

The social structure of the sperm whales species divides on sexual lines. Females are extremely social animals. Females stay in groups of about a dozen individuals and their young. Males leave these "nursery schools" at somewhere between 4 and 21 years of age and join a "bachelor school" with other males of a similar age and size. As males grow older, they tend to disperse into smaller groups, and the oldest males typically live solitary lives. Yet mature males have been stranded on beaches together, suggesting a degree of cooperation not yet fully understood.

Taxonomy and naming

The sperm whale is one of the many species originally described by Linnaeus in 1758 in his eighteenth century work, Systema Naturae. Linnaeus recognized four species in the Physeter genus (Linnaeus 1758). Experts soon realized that just one such species exists.

In most modern publications the sperm whale is classified as the sole species, Physeter macrocephalus, in the family Physeteridae (and thus the only species in its genus). The sperm whale family is sometimes treated as a superfamily, Physeteroidea (Mann et al. 2000). This superfamily contains only two other species—the pygmy sperm whale and the dwarf sperm whale. These two whales are placed in the family Kogiidae.

Mead and Brownell (1993), however, list all three species (sperm whale, pygmy sperm whale, and dwarf sperm whale) in the family Kogiidae, giving the sperm whale the binomial name Physeter catodon and dispensing with the superfamily.

The following is an extract from Melville's Moby-Dick, in which he expatiates about the naming and common lore surrounding the sperm whale:

This whale, among the English of old vaguely known as Trumpa whale, and the Physeter whale, and the Anvil Headed whale, is the present Cachalot of the French, the Pottfisch of the Germans, and the Macrocephalus of the Long Words. […] It is chiefly with his name that I now have to do. Philologically considered, it is absurd. Some centuries ago, when the sperm whale was almost wholly unknown in his proper individuality, and when his oil was only accidentally obtained from the stranded fish; in those days spermaceti, it would seem, was popularly supposed to be derived from a creature identical with the one then known in England as the Greenland or Right Whale. It was the idea also, that this same spermaceti was that quickening humor of the Greenland Whale which the first syllable of the word literally expresses. In those times, also, spermaceti was exceedingly scarce, not being used for light, but only as an ointment and medicament. It was only to be had from the druggists as you nowadays buy an ounce of rhubarb. When, as I opine, in the course of time, the true nature of spermaceti became known, its original name was still retained by the dealers; no doubt to enhance its value by a notion so strangely significant of its scarcity. And so the appellation must at last have come to be bestowed upon the whale from which this spermaceti was really derived.
 
— Melville's Moby Dick, Chapter 32, named "Cetology"

Sperm whales are believed to have diverged from other toothed whales early in the evolution of the suborder—around twenty million years ago (Nikaido et al. 2001).

Conservation

Skeleton of a sperm whale

Population and hunting

The number of sperm whales throughout the world is unknown. Crude estimates, obtained by surveying small areas and extrapolating the result to all the world's oceans, range from 200,000 to 2,000,000 individuals.

Although the sperm whale was hunted for several centuries for its meat, oil, and spermaceti, the conservation outlook for sperm whales is brighter than that for many other whales. Although a small-scale coastal fishery still occurs in Indonesia, they are protected practically worldwide. Fishermen do not catch the deep-sea creatures that sperm whales eat, and the deep sea is likely to be more resistant to pollution than surface layers.

However, the recovery from the whaling years is a slow process, particularly in the South Pacific, where the toll on males of a breeding age was severe.

Watching sperm whales

Female in Dominican Pod, 2005

Sperm whales are not the easiest of whales to watch, due to their long dive times and ability to travel long distances underwater. However, due to the distinctive look and large size of the whale, watching is increasingly popular. Sperm whale watchers often use hydrophones to listen to the clicks of the whales and locate them before they surface.

Popular locations for sperm whale watching include the picturesque Kaikoura on New Zealand's South Island, where the continental shelf is so narrow that whales can be observed from the shore, Andenes and Tromsø in Arctic Norway, and at the Azores where it can be seen throughout the year as opposed to other whales that are only seen during migration. Dominica is believed to be the only Caribbean island with a year-round residential pod of females and calves.

References

  • American Cetacean Society (ACS). 2004. Sperm whale. American Cetacean Society Fact Sheet. Retrieved December 10, 2007.
  • Carwardine, M. 1994. On the Trail of the Whale. Thunder Bay Publishing. ISBN 1899074007.
  • Carwardine, M., and E. Hoyt. 1998. Whales & Dolphins. The Nature Company guides. London: HarperCollins. ISBN 0002201054.
  • Cranford, T. W. 2007. Faculty profile. Spermwhale.org. Retrieved December 10, 2007.
  • Folkens, P. A., and R. R. Reeves. 2002. Guide to Marine Mammals of the World. New York: A.A. Knopf. ISBN 0375411410
  • Gander Academy (GA). 2001. Sperm whales. Gander Academy. Retrieved December 10, 2007.
  • Linnaeus, C. 1758. Systema Naturae per Regna Tria Naturae, Secundum Classes, Ordines, Genera, Species, cum Characteribus, Differentiis, Synonymis, Locis. Tomus I. Editio Decima, Reformata. Holmiae. (Laurentii Salvii).
  • Mann, J. 2000. Cetacean Studies: Field Studies of Dolphins and Whales. Chicago: University of Chicago Press. ISBN 0226503410.
  • Møhl, B., M. Wahlberg, P. T. Madsen, A. Heerfordt, and A. Lund. 2003. The monopulsed nature of sperm whale clicks. J. Acoust. Soc. Am. 114: 1143-1153.
  • Mead and Brownell. 1993. In D. E. Wilson and D. M. Reeder (Eds.), Mammal Species of the World: A Taxonomic and Geographic Reference (Smithsonian Series in Comparative Evolutionary Biology). Washington: Smithsonian Institution Press. ISBN 1560982179.
  • Moore, M. J., and G. A. Early. 2004. Cumulative sperm whale bone damage and the bends. Science 306(5705): 2215. PMID 15618509.
  • Perrin, W. F., B. Würsig, and J. G. M. Thewissen. (Eds.) 2002. Encyclopedia of Marine Mammals. San Diego, CA: Academic Press. ISBN 0125513402.
  • Southwestern Company. 1986. The Volume Library: A Modern, Authoritative Reference for Home and School Use—Clear and complete, Colorfully Illustrated, Totally Indexed, Special Atlas Section. Nashville, Tenn: The Southwestern Co. ISBN 0871972085.

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