Sperm whale

• 1. Introduction

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  The sperm whale, Physeter macrocephalus, makes the loudest sound of any animal on Earth. Its underwater clicks reach a source level of 236 decibels. That volume is only one oddity in a toothed whale that lives in every ocean and hunts squid at great depth. Its females raise young in tight family groups, much as elephants do. For centuries it was also the target of a worldwide hunting industry. How does a mammal this large breathe, feed, and communicate far below the surface? What made its body worth chasing across oceans? And how many of these whales are left today?

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• 2. Names and Wax

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  Spermaceti, a semi-liquid wax found inside the animal's head, gave the sperm whale its name. Early observers mistook the substance for the whale's semen. The name is a shortened form of "spermaceti whale". Another common name, cachalot, probably comes from an old French word for "tooth" or "big teeth". That root survives in the Gascon dialect as caishau. The etymologist Corominas calls the origin uncertain and suggests the Vulgar Latin cappula, meaning sword hilts. The Russian word kashalot keeps the old term alive.

  The scientific name tells its own story. Physeter comes from a Greek word meaning blowpipe or blowhole, and macrocephalus means big-headed. A rival name, catodon, means down-tooth. It refers to the fact that visible teeth appear only in the lower jaw.

  The Swedish ichthyologist Peter Artedi described the animal in his 1738 work Genera piscium. He relied on reports of beached specimens, one in Orkney in 1693 and two in the Netherlands in 1598 and 1601. Carl Linnaeus then included the species in the 10th edition of Systema Naturae in 1758. He listed four species, but experts soon realised that only one exists.

  The argument over which name was valid ran for generations. Until 1974, the species was generally called P. catodon. That year the Dutch zoologists Antonius Husson and Lipke Holthuis proposed macrocephalus instead, citing the principle of the First Reviser. Most authors followed, and the Society for Marine Mammalogy now uses macrocephalus in its official species list. Schevill argued in 1986 and 1987 that only catodon could be valid. The ITIS database nonetheless switched to macrocephalus, following Holthuis.

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• 3. Giant Proportions

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  A bull sperm whale in its prime averages 16 m in length and about 45 tonnes. A typical female measures 11 m and 15 tonnes. Newborns of both sexes are roughly 4 m long and weigh about 1 tonne. Mature males end up 30 to 50 percent longer than females and three times as massive, a gap that places the species among the most sexually dimorphic of all cetaceans. The next largest toothed whale, Baird's beaked whale, reaches only about 13 m and 14 tonnes.

  Record claims are slippery. A Soviet whaling fleet reported a 20.7 m animal near the Kuril Islands in 1950, estimated at 80 tonnes. Researchers reviewing size data supported a 24 m male from the South Pacific in 1933 as the longest on record. Many older reports of 80 feet or more are treated as exaggerations, or as measurements taken along the curve of the body. Ninety-five percent of recorded animals were shorter than 15.85 m. Whaling probably shrank the average size. Another view holds that hunting barely affected bulls and that they may even be larger now because of density effects.

  One-quarter to one-third of a sperm whale's length is head. The snout is blunt and square. An S-shaped blowhole sits near the front and is shifted to the left, which sends a bushy spray forward at an angle. Instead of a dorsal fin, the back carries a series of ridges on its rear third. Whalers called the largest ridge the hump. The triangular flukes are thick and flexible, and they are larger relative to the body than those of any other cetacean. Where most large whales have smooth skin, the sperm whale's back is wrinkled, and whale watchers compare it to a prune.

  Each side of the narrow, underslung lower jaw holds 18 to 26 cone-shaped teeth, and a single tooth can weigh up to 1 kg. Oddly, the teeth seem unnecessary for eating squid, since well-fed whales have turned up toothless or with deformed jaws. One idea is that the teeth matter in fights between males, who often carry scars. Researchers read a whale's age from its teeth, which build layers of cementum and dentine much as trees add rings.

  The nasal openings in the skull sit skewed toward the left, which makes the whole skull asymmetrical. Inside sits the largest brain of any animal, living or extinct. It averages 7.08 kg, with a recorded range from 6.4 to 9.2 kg. That is more than five times the mass of a human brain, with a volume of about 8,000 cubic centimetres. Size alone does not settle intelligence, however. The sperm whale scores lower on the encephalization quotient than many dolphins and whales, and lower than non-human apes. The olfactory system is reduced, suggesting poor taste and smell, while the auditory system is enlarged.

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• 4. Deep Dives

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  Eight minutes at the surface is about all a sperm whale spends between dives. During that pause it blows three to five times a minute at rest, rising to six or seven times after a dive. The blow is a noisy single stream that climbs 2 m or more and points forward and left at about 45 degrees. Then the flukes lift high out of the water and the whale descends. A typical dive reaches about 400 m and lasts around 35 minutes. The deepest dives go to 2250 m and can last up to 120 minutes.

  Several adaptations make this possible. The ribs join the spine through flexible cartilage, so the ribcage can collapse under pressure instead of snapping. Collapsing lungs reduce how much nitrogen enters the body, and the metabolism can slow to save oxygen. Muscle holds far more myoglobin than in land animals, and the blood is dense with red cells. When oxygen runs low, blood can be routed to the brain and other vital organs alone.

  Deep diving still leaves marks. Skeletons show avascular necrosis, the same bone damage that signals decompression sickness in people. Older skeletons showed the most damage and calves showed none. That pattern suggests the whales may be vulnerable to the bends, and that a sudden rise to the surface could kill one. Rest comes in short bouts, with pods sometimes hanging vertically with their heads at the surface. A 2008 study in Current Biology found evidence that the whales may sleep with both sides of the brain. They seem to fall into deep sleep about 7 percent of the time, most often between 6 p.m. and midnight.

  A famous idea about buoyancy involves the wax in the head. According to the hypothesis, cold water entering the organ before a dive solidifies the wax and raises its density. That would produce a downward force of about 392 N. Heat from hunting would melt the wax again and help the whale rise. More recent work found problems. The head lacks anatomy suited to the needed heat exchange, and solid wax would impair echolocation just when the whale needs it.

  Tagging studies show that sperm whales hunt upside down at the bottom of their dives. One suggestion is that they pick out squid as silhouettes against dim light from above. The diet is mainly medium-sized squid. A study around the Galápagos found that squid of the genus Histioteuthis made up 62 percent of what the whales took. Giant squid and colossal squid are on the menu too, along with octopuses, rays, and sharks. No human has watched a battle between a sperm whale and a giant squid, but white scars on the whales are believed to come from them. A study published in 2010 suggested that females may cooperate when hunting Humboldt squid. Adults eat about 3 percent of their body weight each day.

  Food passes into a four-chambered stomach. The first chamber has thick muscular walls and secretes no gastric juice. It crushes prey, since whales cannot chew, and it resists the claws and suckers of swallowed squid. Digestion happens in the second chamber, where as many as 18,000 undigested squid beaks have been found in a dissected animal. Most beaks are vomited up. A beak that reaches the intestine, which can exceed 300 m in length, irritates it, and the whale secretes ambergris in response. Scientists compare the process to a pearl forming in an oyster. Beachcombers still search the shore for the waxy lump as flotsam.

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• 5. Click Language

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  On a research vessel in May 1959, Valentine Worthington and William Schevill made the recording that proved sperm whales produce focused clicks. The machinery behind those clicks sits on top of the skull. A barrel-like organ is filled with spermaceti, a liquid blend of fats and waxes, and wrapped in a tough fibrous wall called the case. The case can hold up to 1,900 litres, and it is proportionally larger in males. The share of wax esters rises with age, from 38-51 percent in calves to 58-87 percent in adult females and 71-94 percent in adult males.

  Each click begins at the front of the nose. Air forced through a single pair of phonic lips, nicknamed monkey lips, makes the sound. Other toothed whales have two pairs, and theirs sit behind the melon. The sound travels backward through the spermaceti organ and bounces off the frontal sac at the rear of the skull. That surface is covered in fluid-filled knobs 4-13 mm across. The grooves between them trap a film of air that stays constant at any depth or orientation, which makes an excellent sound mirror. The reflected energy then passes forward through the junk, a lens-like structure that focuses it into a beam.

  Sound bounces back and forth inside the organ over a few milliseconds. That stamps each click with a multi-pulse structure. The spacing between pulses tracks the length of the organ, so researchers can measure a whale's head from its click alone. Every individual's click is distinct, and it shifts in tone as the organ grows with age. Echoes return mainly through the lower jaw and travel along a fat-filled canal to the inner ear. The air comes from the right nasal passage and is recycled back through the left, so the whale can keep clicking for as long as it stays submerged. Evolution is thought to have turned the ancestor's left nostril into the blowhole and its right nostril into the phonic lips.

  Four kinds of click are recognised. Ordinary echolocation clicks search for prey. Creaks, a rapid series that sounds like a creaky door hinge, guide the whale in on a target. Slow clicks are heard only around males, who make them 74 percent of the time on breeding grounds. That suggests they are mainly mating signals. A popular guess is that the clicks stun prey. Experiments have not reproduced the supposed injuries, and sound pressure levels reaching squid were more than an order of magnitude below those needed to debilitate.

  Codas are the most distinctive sounds, short rhythmic sequences that mostly contain 3-12 clicks. Whales learn them within a stable social group. Since sperm whales spend over 70 percent of their time foraging alone, researchers suggest codas "could help whales reunite and reaffirm their social ties in between long foraging dives". Acoustic tools can tell individual whales apart by tiny features, and the whales can probably do the same. That does not prove they deliberately sign their names the way bottlenose dolphins use signature whistles.

  Some codas announce membership in a clan. Seven clans have been described among the roughly 150,000 female sperm whales of the Pacific Ocean, and another four live in the Atlantic. Whales will not group with another clan, even when they share the same waters. Statistically, the more two clans' ranges overlap, the sharper the difference between their identity codas.

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• 6. Pods and Predators

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  "The foundation of sperm whale society is the matrilineally based social unit of ten or so females and their offspring. The members of the unit travel together, suckle each others' infants, and babysit them while mothers make long deep dives to feed." So runs one scientific description of the species. Units are most commonly six to nine whales and can top twenty. Individuals rarely, if ever, join or leave. Unlike orcas, members show no marked tendency to be genetic relatives. Females and calves spend about three-quarters of their time foraging and a quarter socializing, usually in the afternoon. They spend much of that social time rubbing against one another.

  Males follow a different path. At sexual maturity, between 9 and 21 years of age, a young bull moves to higher latitudes, where colder water offers richer feeding. Females stay at lower latitudes. Bulls may form loose bachelor groups with males of similar age and size, then turn solitary as they age. They return to a pod only to socialize or breed. Bulls have been found beached together, which hints at a form of cooperation that is not yet understood. Mating appears to depend on female choice. A 40-year study around the Galápagos Islands recorded only one case of aggression between males over 11 years, and a 20-year study off the Dominican Republic recorded none.

  Gestation lasts 14 to 16 months and produces a single calf. A mature female gives birth once every 4 to 20 years. Birth is a social event, because mother and calf need others to guard them from predators. The adults may jostle and bite the newborn during its first hours. Milk is about 36 percent fat, against 4 percent in cow's milk, with a texture like cottage cheese that keeps it from dissolving before the calf can drink. Nursing lasts 19 to 42 months, though a calf may rarely suckle for up to 13 years. Calves may also nurse from females other than their mothers. Females appear to reach sexual maturity around age 9, and the oldest pregnant female on record was 41. The oldest recorded whale lived to 77-80 years.

  Orcas are the most common natural predator. They target groups of females with young and try to pull out and kill a calf. Pilot whales and false killer whales sometimes harass sperm whales. The defenders encircle a calf or an injured adult. They may face inward with their tails out, a pattern called the marguerite formation after the flower, or face outward in a heads-out formation. A sperm whale's powerful tail can deliver a lethal blow. Bulls are believed to be too large and aggressive to be threatened. Several orca hunts on bulls have been documented, and none succeeded. A 2013 study found that males answered recorded orca sounds with deep dives and quieter vocal activity. Sperm whales rarely bond with other species, but one bottlenose dolphin with a spinal deformity was accepted into a pod.

  The circling instinct has a grim side. Early whalers exploited it by wounding one member to draw in the whole unit. Melville's Moby-Dick describes the tactic, noting that the companions of a struck female swim around her "with every token of concern". Some linger so long that they become prey themselves.

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• 7. Chasing Spermaceti

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  According to legend, a captain named Christopher Hussey was cruising for right whales near shore around 1712 when a northerly wind blew him out to sea. There he met a pod of sperm whales and killed one. The story may not be true. Judge Paul Dudley, writing in 1725, credited a man named Atkins with being among the first to catch sperm whales, around 1720 off New England. Before that, hunting had been done mostly by indigenous Indonesians.

  Spermaceti candles changed the economics. By the early 1740s, American vessels began to focus on sperm whales. The diary of Benjamin Bangs records three other sloops cutting up sperm whales off North Carolina in late May 1743. Back in Nantucket in the summer of 1744, he noted that "45 spermacetes are brought in here this day".

  The hunt spread fast, reaching West Africa in 1763, the Azores in 1765, and the South Atlantic in the 1770s. From 1770 to 1775, ports in Massachusetts, New York, Connecticut, and Rhode Island produced 45,000 barrels of sperm oil a year, against 8,500 of ordinary whale oil. The British joined in with American ships and crews, and the French followed with American expertise. Fleets grew from small sloops carrying one or two whaleboats to larger ships. Those ships sailed to the equatorial Pacific, the Indian Ocean, Japan, the coast of Arabia, Australia, and New Zealand.

  Spermaceti and sperm oil ended up in candles, soap, cosmetics, machine oil, lamp oil, pencils, crayons, leather waterproofing, rust-proofing materials, and many pharmaceutical compounds. Ambergris, a costly, flammable wax from the digestive system, was prized as a fixative in perfume. Lighthouses in the United States burned spermaceti oil until 1862, when lard oil replaced it and petroleum later replaced that. The oil also lubricated machines in the cotton mills of the Industrial Revolution. Sperm whaling declined in the second half of the 19th century as petroleum spread. In that sense, petroleum arguably spared the whales even heavier exploitation.

  The work was dangerous because bulls fight back, using the huge head as a battering ram. On the 20th of November 1820, a whale claimed to be about 25.9 m long rammed and sank the Nantucket whaleship Essex. Only eight of the twenty remaining sailors survived to be rescued by other ships. The episode is popularly believed to have inspired Herman Melville's Moby-Dick. Melville linked the animal to the Leviathan of the Bible. In Jules Verne's 1870 novel Twenty Thousand Leagues Under the Seas, the Nautilus fights a group of "cachalots" that Verne portrays as savage hunters, "nothing but mouth and teeth".

  Across the Pacific, sperm whale teeth were already treasured. The Māori call whale tooth pendants rei puta. They were rare objects, because sperm whales were not actively hunted in traditional Māori society and ivory came from beached animals. In Fiji the teeth are known as tabua. They were given as gifts of atonement or esteem, a custom called sevusevu, and they mattered in negotiations between rival chiefs. In 1896, Friedrich Ratzel reported that whale teeth were the most-demanded article of ornament or value in Fiji, often worn in necklaces. The tabua remains important in Fijian life today. Teeth had been rare in Fiji and Tonga, which exported them. When Europeans arrived, teeth flooded the market and the "currency" collapsed. The oversupply fed the development of the European art of scrimshaw.

  About 30 teeth from each whale can serve as ivory. Each is up to 20 cm long and 8 cm across, and hollow for the first half of its length. Whalers carved and inked them into scrimshaw, a craft practised widely in the 19th century. Scrimshaw made from genuine sperm whale ivory declined substantially after the whaling fleets were retired in the 1880s.

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• 8. Recovery and Risk

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  In both the 1941-42 and 1942-43 seasons, Norwegian expeditions took more than 3,000 sperm whales off the coast of Peru alone. Modern whaling was far more efficient than open-boat hunting, using steam-powered ships and exploding harpoons. It first targeted large baleen whales, and sperm whaling grew as those populations were depleted. After World War II, the hunt continued unabated to supply oil for cosmetics and for high-performance machinery such as automobile transmissions.

  The numbers are stark. Before commercial hunting began in the early 18th century, the worldwide population is estimated at 1,100,000. By 1880 it had fallen by an estimated 29 percent. It partly recovered until 1946 as whaling eased, then dropped to 33 percent of the pre-whaling total. Whaling nations killed between 184,000 and 236,000 sperm whales in the 19th century and at least 770,000 in the 20th. Most of the 20th-century toll fell between 1946 and 1980.

  Bans on whale oil use arrived in 1972. The International Whaling Commission gave the species full protection in 1985, although Japanese hunting in the northern Pacific continued until 1988. Records show that Japanese vessels caught 51 sperm whales in the 11-year period starting in 2000. Today the species is protected almost worldwide. Listing under Appendix I of CITES prohibits commercial international trade in whales and their parts, and the Convention on the Conservation of Migratory Species lists the sperm whale on its Appendices I and II.

  The global population is now estimated at 360,000. That is why the International Union for Conservation of Nature rates the species vulnerable, while the United States Endangered Species Act lists it as endangered. Recovery is slow, especially in the South Pacific, where the toll on breeding-age males was severe. Since the 2000s, entanglement in fishing nets and collisions with ships have been the greatest threats. Others include marine debris, ocean noise, and chemical pollution. Since the 1970s, some sperm whales have turned up with pieces of plastic in their stomachs.

  The whales' absence is felt at sea. In the Southern Ocean, their iron-rich faeces fertilise surface phytoplankton, which draw carbon from the air and carry it to the deep when they die. Because whaling reduced sperm whale numbers there, an extra 2 million tonnes of carbon stays in the atmosphere each year.

  In 1975, Connecticut's General Assembly named the sperm whale its state animal. Lawmakers cited the species' contribution to the state's history and its present-day plight as an endangered species. Watching the animals is not easy, because of their long dives and the distances they travel underwater. Even so, it grows more popular. Watchers use hydrophones to listen for clicks before the whales surface. Popular sites include Kaikōura on New Zealand's South Island, Andenes and Tromsø in Arctic Norway, and the Azores, where the narrow continental shelf lets people see whales from shore. On Dominica, The Dominica Sperm Whale Project has run a long-term scientific research program since 2005.

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