Sperm whale range (in blue)
The sperm whale (Physeter macrocephalus or Physeter catodon) is the largest of all toothed whales and largest living toothed animal. The whale was named after the milky-white waxy substance, spermaceti, found in its head and originally mistaken for sperm or semen. Historically, the sperm whale has also been known as the common cachalot; "cachalot" is derived from an archaic French word for "tooth".
Over most of the period from the early 18th century until the late 20th century, the sperm whale was subjected to significant hunting pressure in order to obtain the spermaceti and other products, such as sperm oil and ambergris. Spermaceti found many important uses, such as candles, soap, cosmetics and machine oil. Due to its size, the sperm whale could sometimes defend itself effectively against whalers, a famous example being the Essex. As a result of whaling pressure, the sperm whale is currently listed as vulnerable by the IUCN. The sperm whale has few natural enemies, as few predators are strong enough to successfully attack a healthy sperm whale, however orcas have been observed attacking pods and killing adult sperm whales. The sperm whale can live for more than 70 years.
"Sperm whale" is an apocopation of Spermaceti Whale. Spermaceti is the semi-liquid, waxy substance found in the animal's head. Spermaceti is found in the spermaceti organ or case in front of and above the skull of the whale and also in the junk, the area below the spermaceti organ and just above the upper jaw.[3] The case consists of a soft white, waxy substance saturated with spermaceti oil. The junk is composed of cavities filled with the same wax and spermaceti oil and intervening connective tissue.[4][5][3]
The sperm whale is also known as the "cachalot", which is thought to be derived from an archaic French word for "tooth", for example cachau in the Gascon dialect.[6]. The etymological dictionary of Corominas says the origin of the word is uncertain, but it suggests that it comes from the vulgar Latin cappula, plural of cappulum, hilt of a sword.[7] According to Encarta Dictionary, the word cachalot came to English "via French from Spanish or Portuguese cachalote, perhaps from [Portuguese] cachola, 'big head'".
[edit]Description
[edit]Size
Average sizes[8] Length Weight
Bull 16 metres (52 ft) 41,000 kilograms (40 LT; 45 ST)
Cow 11 metres (36 ft) 14,000 kilograms (14 LT; 15 ST)
Newborn 4 metres (13 ft) 1,000 kilograms (0.98 LT; 1.1 ST)
It is among the most sexually dimorphic of all cetaceans, meaning males and females differ greatly. Mature males are typically 30% to 50% longer than mature females and three times as massive.[4] However at birth both sexes are about the same size.[8]
[edit]External appearance
The sperm whale's distinctive shape comes from its very large head, which is typically one-third of the animal's length. The blowhole is located very close to the front of the head and shifted to the whale's left.[4] This gives rise to a distinctive bushy blow angled forward.
The sperm whale's flukes are also triangular and very thick. Flukes are lifted very high out of the water before a whale begins a deep dive.[4] The sperm whale has no true dorsal fin. Instead, a series of ridges are present on the caudal third of the back. The largest ridge was called the 'hump' by whalers, and can be mistaken for a dorsal fin because of its shape.[8]
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.[13] It is normally a uniform grey in colour, though it may appear brown in sunlight. White albino whales have also been reported.[14][15][16]
[edit]Jaws and teeth
The sperm whale has 20 to 26 teeth on each side of its lower jaw.[4] The teeth are cone-shaped and weigh up to 1 kilogram (2.2 lb).[17] The purpose of the teeth is unknown. Teeth do not appear to be necessary for capturing or eating squid, and well-fed sperm whales have been found in the wild without teeth. One hypothesis is that the teeth are used in aggression between males. [18] Bull sperm whales often show scars which seem to be caused by the teeth of other bulls. Rudimentary teeth are also present in the upper jaw, but these rarely emerge into the mouth.[19]
[edit]Respiration and diving
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 kilometres (1.9 mi) in depth and 90 minutes in duration to the ocean floor. More typical dives are around 400 metres (1,300 ft) in depth and 35 minutes in duration.[4] Because of the great depths to which they dive, sperm whales sometimes drown when entangled in transoceanic telephone cables.[20]
[edit]Brain and senses
BlowholePhonic lipsDorsal bursaeCraniumMelonBony naresUpper mandibleAuditory bullaeLower mandibleOutgoing soundIncoming sound
Echolocation system of a toothed whale[30][31]
The brain of the sperm whale is the largest known of any modern or extinct animal, weighing on average about 8 kilograms (18 lb).[32][33] However, it is not particularly large in proportion to its body size. For example, the sperm whale has a lower encephalization quotient than many other whale and dolphin species, lower than that of non-human anthropoid apes and much lower than humans'.[33][34]
Like other toothed whales (suborder odontoceti), sperm whales use echolocation as one means to find food because they live in an underwater habitat that has favourable acoustic characteristics and where visual range is limited due to absorption by water and often by suspended material. The whale emits a focused beam of high-frequency clicks covering a wide angle ahead of it. Sounds are generated by passing air from the bony nares through the phonic lips (also known as "monkey lips"), a structure within the head.[30] The skull, melon and various air sacs in the whale's head all play important roles in forming and focusing the beam of sound. Echoes are received using the lower jaw as the primary reception path, from where they are transmitted to the inner ear via a continuous fat-filled canal.[31]
[edit]Functions of spermaceti
Main article: Spermaceti
The spermaceti organs may help in diving by adjusting the whale's buoyancy. Before diving, cold water is brought through the organ and the wax is solidified.[27][35] The increase in specific density generates a down force of about 40 kilograms (88 lb) and allows the whale to dive with minimal effort. During the chase in deep levels (max. 3,000 m) the stored oxygen is consumed and excess heat melts the spermaceti. Now only hydrodynamic forces generated by swimming keep the whale down, and it can surface without effort.[36]
Herman Melville's Moby Dick suggests that the "case" containing the spermaceti evolved as a kind of battering ram for use in fights between males.[37] 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.[38]
Another possibility is that the case is used as an aid to echolocation (see melon).[5] The shape of the organ at any given time is likely to focus or widen the beam of emitted sound.[39] The sperm whale actually has two nostrils — one external nostril (the left one), forming the blow hole, and one internal nostril (the right one) pressing against the bag-like spermaceti container.[5] The male sperm whale's spermaceti organ is much larger than the female's, and this dimorphism may be a case of sexual selection, enabling males to compete for the favours of females by sound displays.[40]
[edit]Ecology, behaviour and life history
[edit]Distribution
The sperm whale is among the most cosmopolitan species in the world, as it is relatively abundant from polar waters to the equator., and is found in all the oceans and the Mediterranean Sea.[8]Although both sexes range through temperate and tropical oceans and seas, only adult males move through the higher latitudes.[14]
It can be found in most marine waters that are over 1,000 metres (3,300 ft) deep and are not covered with ice, with the exception of the Black Sea.[2] Its presence in the Red Sea is uncertain.[2] Both the Black Sea and Red Sea have shallow entrances, which may account for the absence of sperm whales in these waters.[41] The Black Sea's lower layers are also anoxic and contain high concentrations of sulphur compound such as hydrogen sulphide.[42]
Populations are denser close to continental shelves and canyons.[14] 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 and drops quickly to depths of 310–920 metres (1,000–3,000 ft).[8] Coastal areas with significant sperm whale populations include the Azores and the Caribbean island of Dominica.[43]
[edit]Reproduction
Young sperm whale
Sperm whales can live 70 years or more.[8][14][44] They 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.[4]
Females reach sexual maturity at between 7 and 13 years old, but males do not become sexually mature until at least 18 years old. Upon reaching sexual maturity, males move to higher latitudes, where the water is colder and feeding is more productive. Females remain at lower latitudes upon reaching sexual maturity.[8]
Males only reach their full size when about 50 years old.[4]
[edit]Social behavior
Females stay in groups of about a dozen individuals and their young.[4] 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.[4] As males grow older, they tend to disperse into smaller groups, and the oldest males typically live solitary lives.[4] Yet mature males have been stranded on beaches together, suggesting a degree of co-operation which is not yet fully understood.[4]
[edit]Feeding
It is not well understood why the sperm whale has such a large head in comparison to the lower jaw. One theory explaining this is that the sperm whale's ability to echolocate through its head aids in hunting. However squid, its main prey, may have acoustic properties too similar to those of seawater to reflect sounds.[61] The sperm whale's head contains a structure called monkey lips, through which it blows air. This can create clicks that have a source level exceeding 230 decibels re 1 micropascal referenced to a distance of 1 metre (3.3 ft) – in other words it is by far the loudest sound made by any animal, and 10–14 dB louder than a powerful rifle sounds in air at 1 metre (3.3 ft) away.[62] It has been hypothesised that these were directed at prey in order to stun them, however experimental studies attempting to duplicate this effect have been unable to replicate the supposed injuries, and have cast doubt on this idea.[63]
[edit]Taxonomy and naming
The sperm whale belongs to the order Cetacea, the order containing all whales and dolphins. It is a member of the suborder Odontoceti, the suborder containing all the toothed whales and dolphins. It is the sole extant species of its genus, Physeter, which is placed in the family Physeteridae. Two species of the related extant genus Kogia, the pygmy sperm whale Kogia breviceps and the dwarf sperm whale K. simus, are sometimes also placed in this family, or else are placed in their own family, Kogiidae.[64] In some taxonomic schemes the families Kogiidae and Physeteridae are combined as the superfamily Physeteroidea (refer separate entry sperm whale family).[65]
[edit]Evolutionary History
See also: Sperm whale family
[edit]Fossil record
Although the fossil record of whales is generally poor,[67] several extinct fossil genera have been assigned to the clade Physeteroidea, which includes the last common ancestor of the modern sperm whale, pygmy sperm whale and dwarf sperm whale, plus all of that ancestor's descendants. These fossils include Ferecetotherium, Idiorophus, Diaphorocetus, Aulophyseter, Orycterocetus, Scaldicetus, Placoziphius, Zygophyseter and Acrophyseter.[68][61][65] Ferecetotherium, found in Azerbaijan and dated to the late Oligocene (about 28 to 23 million years ago), is the most primitive fossil that has been found which possesses some of the features specific to the sperm whale lineage, such as an asymmetric rostrum ("beak" or "snout").[69] Most known fossils from the sperm whale lineage date from the Miocene period, 23 to 5 million years ago. Diaphorocetus, from Argentina, has been dated to the early Miocene. Fossil sperm whales from the Middle Miocene include Aulophyseter, Idiorophus and Orycterocetus, all of which have been found on the west coast of the United States, and Scaldicetus, found in Europe and Japan.[69][70] Orycterocetus fossils have also been found in the North Atlantic Ocean and the Mediterranean Sea, in addition to the west coast of the United States.[71] Placoziphius, found in Europe, and Acrophyseter, from Peru, are dated to the late Miocene.
Evolutionary family tree of sperm whales[72],
including simplified summary of extinct groups (†)[61]
Fossil sperm whales differed from modern sperm whales in the number of teeth and the shape of the face and jaws.[69] For example Scaldicetus had a tapered rostrum.[70] Genera from the Oligocene and early and middle Miocene, with the possible exception of Aulophyseter, had teeth in their upper jaws.[69] Acrophyseter, from the late Miocene, also had teeth in both the upper and lower jaws as well as a short rostrum and an upward curving mandible (lower jaw).[65] These anatomical differences suggest that fossil species may not have necessarily been deep-sea squid eaters like the modern sperm whale, but that at least some genera mainly ate fish.[69] Zygophyseter, dated from the middle to late Miocene and found in southern Italy, had teeth in both jaws and appears to have been adapted to feed on large prey, rather like the modern Orca (Killer Whale).[61]
[edit]Phylogeny
[edit]Relationship with humans
Nantucket, in red, is an island off the state of Massachusetts where much sperm whaling originated
Sperm whaling in the 18th century began with small sloops carrying only a pair of whaleboats (sometimes only one). The scope and size of the fleet increased over time, and eventually larger ships were introduced. In the late 18th and early 19th century sperm whaling ships were sent to the Pacific, the Indian Ocean, Japan, the coast of Arabia, Australia and New Zealand.[84][87][88] Hunting for sperm whales could be dangerous to the crew. For example, on November 20, 1820, a sperm whale claimed to be about 25.9 m (85 ft) long attacked the Nantucket whaleship Essex. Only 8 out of the 21 sailors managed to survive and be rescued by other ships.[89]
Remaining sperm whale populations are large enough that the species' conservation status is rated as vulnerable rather than endangered.[2] 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.[92]
[edit]Current conservation status
The number of sperm whales throughout the world is unknown, but is thought to be in the hundreds of thousands.[2] Although the sperm whale was hunted for several centuries for its meat, oil, ambergis, and spermaceti, the conservational outlook for sperm whales is brighter than for many other whales. Historically, Japan has taken ten sperm whales a year, and until 2006 tens of these whales were hunted off Indonesia. They are protected practically worldwide, and commercial whaling has ceased.[2] Fishermen do not catch the deep-sea creatures that sperm whales eat.[2] However, long-line fishing operations in the Gulf of Alaska have complained about sperm whales stealing fish off their lines.[54]
Entanglement in fishing nets and collisions with ships represent the greatest threats to the sperm whale population currently.[14] Other current threats include ingestion of marine debris, ocean noise, and chemical pollution.[93] The IUCN regards the sperm whale as being "vulnerable" from a conservation standpoint.[2]
[edit]Cultural importance
The teeth of sperm whales, when mounted on rope, are important cultural objects in throughout the Pacific. In New Zealand to the Māori they are known as "rei puta" and were rare as sperm whales were not actively hunted in traditional Māori society.[94] Whale ivory and bone were sourced from beached whales. In Fiji the teeth are known as tabua and they were traditionally given as gifts for atonement or esteem (called sevusevu), and were important in negotiations between rival chiefs.[95] Today the tabua remains an important item in Fijian life. The teeth were originally rare in Fiji and Tonga, which exported the teeth, but with the arrival of Europeans the market was flooded with teeth and this "currency" collapsed. The oversupply led in turn to the development of the European art of scrimshaw.[96]
The title character of Herman Melville's novel Moby-Dick (which has been described as "the pinnacle of American Romanticism") is a sperm whale.[97][98] Melville associated the sperm whale with the Leviathan of the Bible.[98][99] The fearsome reputation perpetuated by Melville was based on bull whales' ability to fiercely defend themselves from attacks by early whalers, occasionally resulting in the destruction of the whaling ships.
In Jules Verne's Twenty Thousand Leagues Under the Sea, cachalots are mentioned (perhaps incorrectly) as preying on fellow whales.