Sperm Whale (Physeter macrocephalus)
The sperm whale (Physeter macrocephalus) is a marine
mammal species, order Cetacea, a toothed whale (odontocete) having the largest
brain of any animal. The name comes from the milky-white waxy substance,
spermaceti, found in the animal's head. The sperm whale is the only living
member of genus Physeter. The now outdated synonym Physeter catodon refers to
the same species. It is one of three extant species in the sperm whale
superfamily, along with the pygmy sperm whale and dwarf sperm whale.
A mature male can grow to 20.5 metres (67 ft) long. It is the largest living toothed animal. For large males, the head can represent up to one-third of the animal's length. It has a cosmopolitan distribution across the oceans. The species feeds primarily on squid but to some extent on fish, diving as deep as 3 kilometres (9,800 ft), which makes it the deepest diving mammal. Its diet includes giant squid and colossal squid. The sperm whale's clicking vocalization is the loudest sound produced by any animal. The clicking is used for sonar and may also be used for other purposes. These whales live in groups called social units. Units of females and their young live separately from sexually mature males. The females cooperate to protect and nurse their young. Females give birth every three to six years, and care for the calves for more than a decade. The sperm whale has few natural predators, since few are strong enough to successfully attack a healthy adult; orcas attack units and are capable of killing the calves. The sperm whale can live for more than 70 years.
Historically, the sperm whale was also 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 hunted to obtain 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. In the most famous example, a sperm whale attacked and sank the American whale ship Essex in 1820. As a result of whaling, the sperm whale is currently listed as vulnerable by the IUCN.
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 are triangular and very thick. 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. Skin is normally a uniform grey in colour, though it may appear brown in sunlight. Albinos have also been reported.
Jaws and teeth
The sperm whales' lower jaw is very narrow and under slung. The sperm whale has 18 to 26 teeth on each side of its lower jaw which fit into sockets in the upper jaw. The teeth are cone-shaped and weigh up to 1 kilogram (2.2 lb) each. The teeth are functional, but do not appear to be necessary for capturing or eating squid, and well-fed animals have been found without teeth. One hypothesis is that the teeth are used in aggression between males. Mature males often show scars which seem to be caused by the teeth. Rudimentary teeth are also present in the upper jaw, but these rarely emerge into the mouth.
Respiration and diving
Sperm whales, along with bottlenose whales and elephant seals, are the deepest-diving mammals. Sperm whales are believed to be able to reach 3 kilometres (1.9 mi) and remain submerged for 90 minutes. More typical dives are around 400 metres (1,300 ft) and 35 minutes in duration. At these great depths, sperm whales had sometimes become entangled in transoceanic telephone cables and drowned until improvements in laying and maintenance techniques were employed. The sperm whale has adapted to cope with drastic pressure changes when diving. The flexible ribcage allows lung collapse, reducing nitrogen intake, and metabolism can decrease to conserve oxygen. Myoglobin, which stores oxygen in muscle tissue, is much more abundant than in terrestrial animals. The blood has a high red blood cell density, which contain oxygen-carrying hemoglobin. The oxygenated blood can be directed towards the brain and other essential organs only when oxygen levels deplete. The spermaceti organ may also play a role by adjusting buoyancy (see below).
While sperm whales are well adapted to diving, repeated dives to great depths have long term effects. Bones show pitting that signals decompression sickness in humans. Older skeletons showed the most extensive pitting, whereas calves showed no damage. This damage may indicate that sperm whales are susceptible to decompression sickness, and sudden surfacing could be lethal to them.
Between dives, the sperm whale surfaces to breathe for about eight minutes before diving again. Odontoceti (toothed whales) breathe air at the surface through a single, S-shaped blowhole. Sperm whales spout (breathe) 3–5 times per minute at rest, increasing to 6–7 times per minute after a dive. The blow is a noisy, single stream that rises up to 2 metres (6.6 ft) or more above the surface and points forward and left at a 45° angle. On average, females and juveniles blow every 12.5 seconds before dives, while large males blow every 17.5 seconds before dives.
A sperm whale killed 100 miles south of Durban, South Africa after a 1 hour, 50-minute dive and was found with two spiny dogfish sharks, usually found at the sea floor, in its belly.
Brain and senses
The brain is the largest known of any modern or extinct animal, weighing on average about 8 kilograms (18 lb), though 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'.
Nasal complex and spermaceti functions
Early on it was proposed that the nasal complex, which includes the spermaceti organ, the junk bodies, and other associated organs, was used as a battering ram (see below) or for buoyancy regulation (see below); however, researchers' current understanding suggest that the primary function of the spermaceti organ and the associated organs in the nose of the sperm whales are used as part of the world's most powerful natural sonar system.
Due to light absorption by water, most of the ocean is dark beyond a few hundred meters thus limiting visual range. As a result, sperm whales and the other toothed whales (suborder odontoceti) have evolved a system of echolocation as the main way to find food in the darkness of the ocean similar to that used by bats to find food in the darkness of the night sky. When echolocating, the sperm whale emits a directionally focused beam of broadband clicks. Clicks are generated by the forcing of air through a pair of phonic lips (also known as "monkey lips" or "museau de singe") at the front end of the nose, just below the blowhole. The sound then travels backwards along the length of the nose through the spermaceti organ. Most of the sound energy is then reflected off an air sac which sits against the skull and down into the Junk Bodies, where the sound is focused by the junk's lens-like structure. Some of the sound will reflect back into the spermaceti organ and back towards the front of the whale's nose where it will be reflected through the spermaceti organ a third time. This back and forth reflection which happens on the scale of a few milliseconds creates a multi-pulse click structure. This multi—pulse click structure actually allows researchers to measure the whale's spermaceti organ using only the sound of its clicks and given the size of the spermaceti organ relates to the size of the whale, biologists can measure the whales by recording their echolocation clicks. The lower jaw is the primary reception path for the echoes. A continuous fat-filled canal transmits received sounds to the inner ear.
The source of the air forced through the phonic lips is the right nasal passage. While the left nasal passage opens to the blow hole, the right nasal passage has evolved to supply air to the phonic lips. It is thought that the nostrils of the land-based ancestor of the sperm whale migrated through evolution to their current functions, the left nostril becoming the blowhole and the right nostril becoming the phonic lips.
The spermaceti organs may also help adjust the whale's buoyancy. It is hypothesized that before the whale dives, cold water enters the organ, and it is likely that the blood vessels constrict, reducing blood flow, and, hence, temperature. The wax therefore solidifies and reduces in volume. The increase in specific density generates a down force of about 392 Newtons (88 lbf) and allows the whale to dive with less effort. During the hunt, oxygen consumption, together with blood vessel dilation, produces heat and melts the spermaceti, increasing its buoyancy and enabling easy surfacing. However, more recent work have found many problems with this theory including the lack of anatomical structures for the actual heat exchange.
Herman Melville's Moby Dick suggests that the "case" containing the spermaceti had evolved as a kind of battering ram for use in fights between males. However, there are almost no modern accounts of fights between male sperm whales. Apart from a few famous exceptions of the well-documented sinking of the ships Essex and Ann Alexander by attackers estimated to weigh only one-fifth as much as the ships, this hypothesis is not well supported in current scientific literature.
The name sperm whale is an apocopation of spermaceti whale. Spermaceti, originally mistaken for the whales' "sperm", is the semi-liquid, waxy substance found in the spermaceti organ or case in front of and above the skull bone and also in the junk, the area below the spermaceti organ and just above the upper jaw. 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. 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. According to Encarta Dictionary, the word cachalot came to English "via French from Spanish or Portuguese cachalote, perhaps from 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 sperm whale is among the most cosmopolitan species. It prefers 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.
It is relatively abundant from the poles to the equator and is found in all the oceans. It inhabits the Mediterranean Sea, but not the Black Sea, while its 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 310–920 metres (1,020–3,020 ft). Coastal areas with significant sperm whale populations include the Azores and the Caribbean island of Dominica.
Sperm whales can live 70 years or more. They are a prime example of a species that has been K-selected, i.e., their reproductive strategy is associated with stable environmental conditions and comprises a low birth rate, significant parental aid to offspring, slow maturation, and high longevity.
How they choose mates has not been definitively determined. There is evidence that males have dominance hierarchies, and there is also evidence that female choice influences mating. Gestation requires 14 to 16 months, producing a single calf. Lactation proceeds for 19 to 42 months, but calves may suckle up to 13 years (although usually less). Calves can suckle from females other than their mothers. Females generally have birth intervals of three to six years.
Females reach sexual maturity between 7 and 13 years; males follow beginning at 18 years. Upon reaching sexual maturity, males move to higher latitudes, where the water is colder and feeding is more productive. Females remain at lower latitudes. Males reach their full size at about age 50.
Females stay in groups of about a dozen individuals and their young. 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 most common non-human attacker of sperm whales is the orca, but pilot whales and the false killer whale also sometimes harass them. Orcas prey on target groups of females with young, usually making an effort to extract and kill a calf. Female sperm whales repel these attacks by encircling their calves. The adults either face inwards to use their tail flukes against the orcas, or outwards, fighting with their teeth. This Marguerite formation, named after the flower, is also used by whales to support an injured unit member. Early whalers exploited this behavior, 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. 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.
Sperm Whales usually dive between 300 to 800 metres (980 to 2,600 ft), and sometimes 1–2 kilometres (3,300–6,600 ft) to search for food. Such dives can last more than an hour. They feed on several species, notably the giant squid, the colossal squid, octopuses, and diverse fish like demersal rays, but the main part of their diet consists of medium-sized squid. Some prey may be taken incidentally 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 fecal matter. 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 1.4 lb) were the most commonly taken. Battles between sperm whales and colossal squid (which have been measured to weigh nearly 500 kilograms (1,100 lb)) 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.
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 steal 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 100,000,000 short tons (91,000,000 t) — a figure greater than the total consumption of marine animals by humans each year.
It is not well understood why the sperm whale's head is so large in comparison to the lower jaw. One theory 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 seawater to reflect sounds. The sperm whale's head contains a structure called the phonic lips, also known as the monkey lips, through which it blows air. This can create clicks that have a source level up to 176 decibels referenced to a distance of 1 metre (3.3 ft) – making it one of the loudest animals on Earth (compare to the pistol shrimp at 218decibels), and 10–14 dB louder than a powerful rifle sounds in air at 1 metre (3.3 ft) away. It has been hypothesised that clicks attempt to stun prey. Experimental studies attempting to duplicate this effect have been unable to replicate the supposed injuries, casting doubt on this idea.
The traditional view has been that Mysticeti (baleen whales) and Odontoceti (toothed whales) arose from more primitive whales early in the Oligocene period, and that the super-family Physeteroidea, which contains the sperm whale, dwarf sperm whale, and pygmy sperm whale, diverged from other toothed whales soon after that, over 23 million years ago. In 1993–1996 molecular phylogenetics analyses by Milinkovitch and colleagues, based on comparing the genes of various modern whales, suggested that the sperm whales are more closely related to the baleen whales than they are to other toothed whales, which would have meant that Odontoceti were not monophyletic, in other words did not consist of a single ancestral toothed whale species and all its descendants. However more recent studies, based on various combinations of comparative anatomy and molecular phylogenetics, criticised Milinkovitch's analysis on technical grounds and reaffirmed that the Odontoceti are monophyletic.
These analyses also confirm that there was a rapid evolutionary radiation (diversification) of the Physeteroidea in the Miocene period. The Kogiidae (dwarf and pygmy sperm whales) diverged from the Physeteridae (true sperm whales) at least 8 million years ago.
Watching sperm whales
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, Andenes and Tromsř in Arctic Norway; as well as the Azores, where the continental shelf is so narrow that whales can be observed from the shore, and Dominica where a long-term scientific research program, The Dominica Sperm Whale Project, has been in operation since 2005.
Current conservation status
The number of sperm whales throughout the world is unknown, but is thought to be in the hundreds of thousands. The conservation outlook 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. Fishermen do not target the creatures that sperm whales eat. However, long-line fishing operations in the Gulf of Alaska have complained about sperm whales stealing fish from their lines.
Entanglement in fishing nets and collisions with ships represent the greatest threats to the sperm whale population currently. Other current threats include ingestion of marine debris, ocean noise, and chemical pollution. The IUCN regards the sperm whale as being "vulnerable". The species is listed as endangered on the United States Endangered Species Act.
The species is listed on Appendix I and Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix I as this species has been categorized as being in danger of extinction throughout all or a significant proportion of their range and CMS Parties strive towards strictly protecting these animals, conserving or restoring the places where they live, mitigating obstacles to migration and controlling other factors that might endanger them. It is listed on Appendix II as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements. It is also covered by the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS) and Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MOU).