A mother sperm whale and her calf
The sperm whale (Physeter macrocephalus), or cachalot, is the largest of the toothed whales and the largest toothed predator. It is the only living member of genus Physeter, and one of three extant species in the sperm whale family, along with the pygmy sperm whale and dwarf sperm whale of the genus Kogia.
Mature males average 16 metres (52 ft) in length but some may reach 20.5 metres (67 ft), with the head representing up to one-third of the animal's length. Plunging to 2,250 metres (7,382 ft), it is the second deepest diving mammal, following only the Cuvier's beaked whale. The sperm whale's clicking vocalization, a form of echolocation and communication, may be as loud as 230 decibels (re 1 µPa at 1 m) underwater. It has the largest brain of any animal on Earth, more than five times heavier than a human's. Sperm whales can live for more than 60 years.
The sperm whale can be found anywhere in the open ocean. Females and young males live together in groups while mature males live solitary lives outside of the mating season. The females cooperate to protect and nurse their young. Females give birth every four to twenty years, and care for the calves for more than a decade. A mature sperm whale has few natural predators. Calves and weakened adults are taken by pods of orcas.
From the early eighteenth century through the late 20th, the species was a prime target of whalers. The head of the whale contains a liquid wax called spermaceti, from which the whale derives its name. Spermaceti was used in lubricants, oil lamps, and candles. Ambergris, a waste product from its digestive system, is still used as a fixative in perfumes. Occasionally the sperm whale's great size allowed it to defend itself effectively against whalers. The species is now protected by a whaling moratorium, and is currently listed as vulnerable by the International Union for the Conservation of Nature and Natural Resources (IUCN).
Taxonomy and naming
Etymology
The name sperm whale is a clip of spermaceti whale. Spermaceti, originally mistakenly identified as the whales' semen, is the semi-liquid, waxy substance found within the whale's head (see below). The sperm whale is also known as the "cachalot", which is thought to derive from the archaic French for "tooth" or "big teeth", as preserved for example in cachau in the Gascon dialect (a word of either Romance or Basque origin). The etymological dictionary of Corominas says the origin is uncertain, but it suggests that it comes from the Vulgar Latin cappula, plural of cappulum, "sword hilt". The word cachalot came to English via French from Spanish or Portuguese cachalote, perhaps from Galician/Portuguese cachola, "big head". The term is retained in the Russian word for the animal, кашалот (kashalot), as well as in many other languages.
The scientific genus name Physeter comes from Greek physētēr (φυσητήρ), meaning "blowpipe, blowhole (of a whale)", or – as a pars pro toto – "whale". The specific name macrocephalus is Latinized from the Greek makrokephalos (μακροκέφαλος, meaning "big-headed"), from makros (μακρός, "large") + kefalos (κέφαλος, "head").
Its synonymous specific name catodon means "down-tooth", from the Greek elements cat(a)- ("below") and odṓn ("tooth"); so named because it has visible teeth only in its lower jaw. (See: Teeth) Another synonym australasianus ("Australasian") was applied to sperm whales in the southern hemisphere.
Taxonomy
The sperm whale belongs to the order Cetartiodactyla, the order containing all cetaceans and even-toed ungulates. It is a member of the unranked clade Cetacea, with all the whales, dolphins, and porpoises, and further classified into Odontoceti, containing all the toothed whales and dolphins. It is the sole extant species of its genus, Physeter, 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 placed either in this family or in the family Kogiidae. In some taxonomic schemes the families Kogiidae and Physeteridae are combined as the superfamily Physeteroidea (see the separate entry on the sperm whale family).
The sperm whale is one of the species originally described by Linnaeus in 1758 in his eighteenth century work, Systema Naturae. He recognised four species in the genus Physeter. Experts soon realised that just one such species exists, although there has been debate about whether this should be named P. catodon or P. macrocephalus, two of the names used by Linnaeus. Both names are still used, although most recent authors now accept macrocephalus as the valid name, limiting catodon's status to a lesser synonym.[b]
Biology
External appearance
The sperm whale is the largest toothed whale, with adult males measuring up to 20.5 metres (67 ft) long and weighing up to 57,000 kilograms (56 long tons; 63 short tons). By contrast, the second largest toothed whale, Baird's Beaked Whalemeasures 12.8 metres (42 ft) and weighs up to 15 short tons (14,000 kg). The Nantucket Whaling Museum has a 5.5 metres (18 ft)-long jawbone. The museum claims that this individual was 24 metres (80 ft) long; the whale that sank the Essex (one of the incidents behind Moby-Dick) was claimed to be 26 metres (85 ft). A similar size is reported from a jawbone from the British Natural History Museum. A 67-foot specimen is reported from a Soviet whaling fleet near the Kurile Islands in 1950. There is disagreement on the claims of adult males approaching or exceeding 24 metres (80 ft) in length.
Extensive whaling may have decreased their size, as males were highly sought, primarily after World War II. Today, males do not usually exceed 18.3 metres (60 ft) in length or 51,000 kilograms (50 long tons; 56 short tons) in weight. Another view holds that exploitation by overwhaling had virtually no effect on the size of the bull sperm whales, and their size may have actually increased in current times on the basis of density dependent effects. Old males taken at Solander Islands were recorded to be extremely large and unusually rich in blubbers. It is among the most sexually dimorphic of all cetaceans. At birth both sexes are about the same size, but mature males are typically 30% to 50% longer and three times as massive as females. Unusual among cetaceans, the sperm whale's blowhole is highly skewed to the left of the head
The sperm whale's unique body is unlikely to be confused with any other species. The sperm whale's distinctive shape comes from its very large, block-shaped head, which can be one-quarter to one-third of the animal's length. The S-shaped blowhole is located very close to the front of the head and shifted to the whale's left. This gives rise to a distinctive bushy, forward-angled spray.
The sperm whale's flukes (tail lobes) are triangular and very thick. Proportionally, they are larger than that of any other cetacean, and are very flexible. The whale lifts its flukes high out of the water as it begins a feeding dive. It has a series of ridges on the back's caudal third instead of a dorsal fin. The largest ridge was called the 'hump' by whalers, and can be mistaken for a dorsal fin because of its shape and size. In contrast to the smooth skin of most large whales, its back skin is usually wrinkly and has been likened to a prune by whale-watching enthusiasts. Albinos have been reported.
Ecology
Distribution
Sperm whales are among the most cosmopolitan species. They prefer ice-free waters over 1,000 metres (3,300 ft) deep. Although both sexes range through temperate and tropical oceans and seas, only adult males populate higher latitudes. They are relatively abundant from the poles to the equator and are found in all the oceans. They inhabit the Mediterranean Sea, but not the Black Sea, while their presence in the Red Sea is uncertain. The shallow entrances to both the Black Sea and the Red Sea may account for their absence. The Black Sea's lower layers are also anoxic and contain high concentrations of sulphur compounds such as hydrogen sulphide.
Populations are denser close to continental shelves and canyons. 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 to 920 metres (1,020 to 3,020 ft). Coastal areas with significant sperm whale populations include the Azores and Dominica. In Asian waters, whales are also observed regularly in coastal waters in places such as Commander and Kuril Islands, Shiretoko Peninsula, off Kinkasan, vicinity to Tokyo Bay and Boso Peninsula to Izu and Izu Islands, Volcano Islands, Yakushima and Tokara Islands to Ryukyu Islands, Taiwan, Northern Mariana Islands, and so forth. Historical catch records suggest there could have been smaller aggression grounds in the Sea of Japan as well.
Grown males are known to enter surprisingly shallow bays to rest (whales will be in state of rest during these occasions). There are unique, coastal groups reported from various areas among the globe such as Scotland, Shiretoko Peninsula, off Kaikoura, in Davao Gulf. Such costal groups were more abundant in pre-whaling days.
Diet
Sperm whales usually dive between 300 to 800 metres (980 to 2,620 ft), and sometimes 1 to 2 kilometres (3,300 to 6,600 ft), in search of food. Such dives can last more than an hour. They feed on several species, notably the giant squid, but also the colossal squid, octopuses, and fish like demersalrays, but their diet is mainly medium-sized squid. Some prey may be taken accidentally while eating other items. Most of what is known about deep sea squid has been learned from specimens in captured sperm whale stomachs, although more recent studies analysed feces. One study, carried out around the Galápagos, found that squid from the genera Histioteuthis (62%), Ancistrocheirus (16%), and Octopoteuthis (7%) weighing between 12 and 650 grams (0.026 and 1.433 lb) were the most commonly taken. Battles between sperm whales and giant squid or colossal squid have never been observed by humans; however, white scars are believed to be caused by the large squid. One study published in 2010 collected evidence that suggests that female sperm whales may collaborate when hunting Humboldt squid. Tagging studies have shown that sperm whales hunt upside down at the bottom of their deep dives. It is suggested that the whales can see the squid silhouetted above them against the dim surface light.
An older study, examining whales captured by the New Zealand whaling fleet in the Cook Strait region, found a 1.69:1 ratio of squid to fish by weight. Sperm whales sometimes take sablefish and toothfish from long lines. Long-line fishing operations in the Gulf of Alaska complain that sperm whales take advantage of their fishing operations to eat desirable species straight off the line, sparing the whales the need to hunt. However, the amount of fish taken is very little compared to what the sperm whale needs per day. Video footage has been captured of a large male sperm whale "bouncing" a long line, to gain the fish. Sperm whales are believed to prey on the megamouth shark, a rare and large deep-sea species discovered in the 1970s. In one case, three sperm whales were observed attacking or playing with a megamouth.
The sharp beak of a consumed squid lodged in the whale's intestine may lead to the production of ambergris, analogous to the production of pearls. The irritation of the intestines caused by squid beaks stimulates the secretion of this lubricant-like substance. Sperm whales are prodigious feeders and eat around 3% of their body weight per day. The total annual consumption of prey by sperm whales worldwide is estimated to be about 91 million tonnes (100 million short tons). In comparison, human consumption of seafood is estimated to be 115 million tonnes (127 million short tons).
Sperm whales hunt through echolocation. Their clicks are among the most powerful sounds in the animal kingdom (see above). It has been hypothesised that it can stun prey with its clicks. Experimental studies attempting to duplicate this effect have been unable to replicate the supposed injuries, casting doubt on this idea.
It has been stated that sperm whales, as well as other large cetaceans, help fertilise the surface of the ocean by consuming nutrients in the depths and transporting those nutrients to the oceans' surface when they defecate, an effect known as the whale pump. This fertilises phytoplankton and other plants on the surface of the ocean and contributes to ocean productivity and the drawdown of atmospheric carbon.
Social Behavior
Relations within the species
Adult males who are not breeding live solitary lives, whereas females and juvenile males live together in groups. The main driving force for the sexual segregation of adult sperm whales is scramble competition for mesopelagic squid. Females and their young remain in groups, while mature males leave their "natal unit" somewhere between 4 and 21 years of age. Mature males sometimes form loose bachelor groups with other males of similar age and size. As males grow older, they typically live solitary lives. Mature males have beached themselves together, suggesting a degree of cooperation which is not yet fully understood. The whales rarely, if ever, leave their group.
A social unit is a group of sperm whales who live and travel together over a period of years. Individuals rarely, if ever, join or leave a social unit. There is a huge variance in the size of social units. They are most commonly between six and nine individuals in size but can have more than twenty. Unlike orcas, sperm whales within a social unit show no significant tendency to associate with their genetic relatives. Females and calves spend about three quarters of their time foraging and a quarter of their time socializing. Socializing usually takes place in the afternoon.
When sperm whales socialize, they emit complex patterns of clicks called codas. They will spend much of the time rubbing against each other. Tracking of diving whales suggests that groups engage in herding of prey, similar to bait balls created by other species, though the research needs to be confirmed by tracking the prey.
Relations with other species
The most common natural predator of sperm whales is the orca, but pilot whales and false killer whales sometimes harass them. Orcas prey on target groups of females with young, usually making an effort to extract and kill a calf. The adults will protect their calves or an injured adult by encircling them. They may face inwards with their tails out (the 'marguerite formation', named after the flower). The heavy and powerful tail of an adult whale can deliver lethal blorcaows. Alternatively, they may face outwards (the 'heads-out formation'). Early whalers exploited this behaviour, attracting a whole unit by injuring one of its members. If the orca pod is extremely large, its members may sometimes be able to kill adult female sperm whales. Solitary mature males are known to interfere and come to the aid of vulnerable groups nearby. Individual large mature male sperm whales have no non-human predators, and are believed to be too large, powerful and aggressive to be threatened by orcas. In addition, male sperm whales have been observed to attack and intimidate orca pods. An incident was filmed from a long-line trawler: an orca pod was systematically taking fish caught on the trawler's long lines (as the lines were being pulled into the ship) when a male sperm whale appeared to repeatedly charge the orca pod in an attempt to drive them away; it was speculated by the film crew that the sperm whale was attempting to access the same fish. The orcas employed a tail outward and tail slapping defensive position against the bull sperm whale similar to that used by female sperm whales against attacking orcas.
Sperm whales are not known for forging bonds with other species, but it was observed that a Bottlenose Dolphin with spinal deformity had been accepted into a pod of sperm whales. They are known to swim alongside other cetaceans such as humpback, fin, minke, pilot, and orca whales on occasion.
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