Sperm whale

The head is the reason the whale looks the way it does and the reason it was hunted. Inside sits the spermaceti organ — a great mass of waxy oil — with a second fatty body called the junk beneath it, air sacs at front and back, and a pair of phonic lips near the front of the head. The whole complex can run to a third of body length, and it is the largest structure of its kind in any animal.

The current account of what it does is acoustic. Air is driven past the phonic lips to make a click; the click travels backwards through the spermaceti to an air sac against the skull, reflects, passes forward through the junk and leaves the front of the head as a highly directional pulse. The head is simultaneously the generator, the lens and the barrel.

It was not always read this way. The classic 1970 hypothesis was buoyancy: spermaceti solidifies within a temperature range the organ can reach, solid wax is denser than liquid, and cooling it before a dive would help the whale sink. The physical measurements behind that are sound and the idea is elegant. It has not survived the timescales — the temperature changes required are too slow and too small to matter over a forty-five-minute dive — and the field has moved to the acoustic account. It is a good example of a well-argued idea that better data did not support, which is more useful for a reader to see than a tidy consensus.

The rest of the anatomy is asymmetric in a way that follows from the sound system. The single blowhole sits at the front left of the head rather than on top, so the spout goes forward and to the left — the field mark that identifies the species from a distance. Teeth are in the lower jaw only, fitting into sockets in the upper; they erupt late, and animals with damaged or missing jaws have been found well fed, which suggests the teeth are less central to catching squid than they look.

Suction-cup tags recording depth, orientation and the animal's own sound turned a great deal of guesswork into a timetable. Sperm whales spend roughly three quarters of their time in foraging cycles: down to 400–1,200 metres, around forty-five minutes there, then about nine minutes at the surface before doing it again. Clicking begins shortly after descent and continues through the deep phase.

The most useful detail in those recordings is the buzz. Regular clicking is search; a rapid burst of clicks immediately before a manoeuvre is a capture attempt, the same acceleration a bat makes as it closes on an insect. That gave researchers something they had never had — a way to count feeding attempts in an animal nobody can watch — and it is how foraging success became measurable at a kilometre's depth.

What they are catching is the part that dismantles the popular picture. Squid beaks resist digestion and accumulate in the stomach, and beak size predicts the size of the animal it came from, so diet can be reconstructed quantitatively. The counts show hundreds to thousands of beaks per whale, dominated numerically by medium-sized squid roughly the size of a forearm. Giant squid beaks do turn up — the encounters are real — and they are a very small fraction of the total.

So the battle with the kraken is a story about a rare event told as though it were the animal's job. The sucker scars are real too, and they mostly grow with the whale rather than recording last week; a scar acquired young stretches as the animal does. The actual life is stranger than the myth: descending into total darkness for three quarters of an hour at a time, hunting by sound, thousands of times a year.

The physiology supporting that is the standard deep-diving mammal package taken to an extreme — oxygen stored in blood and muscle rather than lungs, a lung that collapses under pressure rather than resisting it, heart rate dropping sharply, circulation redirected. The collapse is the counter-intuitive part: it is deliberate, and it prevents nitrogen being forced into the blood at depth.

A single hydrophone cannot measure how loud something is, because what arrives depends on how far away the source was and which way it was pointing, and neither is known. Using an array of hydrophones at known separations fixes that: the whale's position can be computed from arrival times and its orientation inferred from how the click differs across receivers. With range and aim known, source level becomes a measurement. On-axis clicks come in around 230 decibels re 1 micropascal at 1 metre — the highest recorded for any animal.

That figure is then routinely misused, and the arithmetic is worth doing once. Underwater sound pressure levels are quoted against a reference pressure of 1 micropascal; airborne levels use 20 micropascals, and the two media differ in impedance as well. Converting an underwater figure to the airborne scale people know removes roughly 62 units before any comparison is meaningful. A number that sounds apocalyptic on the familiar scale is not on the familiar scale.

Two further things constrain it. It is an on-axis maximum measured at a metre — a convention, since no receiver is ever at a metre — from an animal that beams its sound forwards and downwards to find squid. And there is no documented case of a person being harmed by sperm whale echolocation; divers work around these animals. That is an absence of reports rather than a safety study, and it should be labelled as such, but it is the state of the evidence.

Two quite different sounds get merged in coverage. Echolocation clicks are foraging sonar: enormously loud, directional, aimed at squid. Codas are short rhythmic patterns of a few clicks, far quieter, exchanged between animals at the surface while socialising. The huge decibel figures belong to the first and the "conversations" belong to the second, and almost every popular account attaches one to the other.

Which codas a whale uses turns out to be learned. Recording repertoires from many social units across the South Pacific and Caribbean and clustering them by similarity produced a small number of distinct types — clans — which then failed entirely to line up with geography. Units of different clans share the same water without sharing repertoire; units thousands of kilometres apart share one. Clan membership is not predicted by maternal lineage either. Place and inheritance are both excluded, and what remains is learning from the whales you grow up among.

Calling that culture is a defensible technical use of the word: group-typical behaviour transmitted socially rather than genetically. It does not mean the codas mean things, and it does not mean clans have traditions in any richer sense. The claim is that whales learn what to say from other whales, which is quite large enough on its own.

In 2024, machine-learning analysis of around nine thousand codas from one identified Caribbean clan looked not just at each coda alone but at its timing relative to the codas around it. It found two dimensions of variation nobody had catalogued — smooth variation in overall duration, and an extra click added at the end — which vary with conversational context rather than randomly, and which combine with the known rhythm and tempo categories to give a far larger inventory of distinguishable coda types than the traditional catalogue allowed.

This became "scientists discover sperm whale alphabet". What was demonstrated is structure: the signal varies along more dimensions than anyone knew, and the variation tracks context rather than being noise. What was not demonstrated, and what the paper does not claim, is that any of it means anything. No coda type has been linked to a referent; none has been shown to make a receiving whale do anything.

• Detected: combinatorial structure varying with conversational context, in one clan.
• Demonstrated: which repertoire a whale uses is socially learned rather than inherited or local.
• Not demonstrated: that any coda refers to anything, or has any specific effect on a listener.
• Not implied: syntax, vocabulary, or anything requiring the word "language".

The comparison that keeps this honest is birdsong. Birdsong has rich combinatorial structure, learned dialects and enormous variety, and carries essentially no semantics — the structure is real and does not indicate a language. Finding structure is a necessary first step towards testing for meaning; it is not evidence of it. The search space has been mapped and the search has not yet been run.

Independent evidence that these animals transmit information socially, and fast, comes from an unlikely archive. When American whalers opened the North Pacific they met a population that had never seen a ship, and their logbooks recorded sightings and strikes voyage by voyage. Strike rate fell by around 60% within a few years — too fast for evolution, and too widespread for personal experience, since most whales encountering a ship had not survived a previous attack. The recorded defence also changed, from the surface bunching that works against orcas to swimming fast upwind, which is precisely what a square-rigged ship cannot follow.

Sperm whale society is split by sex to an unusual degree. Females and young live in stable units of around ten animals, largely related, in warmer waters roughly between 40°N and 40°S. Calves cannot follow their mothers to depth, so a unit babysits: while one female forages, another stays at the surface with the calf. Allosuckling — a calf nursing from a female that is not its mother — is documented.

Males leave the natal unit in adolescence and head for higher latitudes, eventually to the ice edges, where the feeding is better and where they grow much larger than females — the strongest sexual size dimorphism of any whale. Mature males then travel back to warm water to breed, moving between units rather than holding a group. The result is that most sperm whale society, and nearly all of its culture, is female.

The strangest thing sperm whales do is one of the few animal facts where the odd popular version is simply correct: they rest vertically, drifting motionless in the upper water column with the head up or down, in silent groups. Bouts last around ten to fifteen minutes and account for roughly 7% of the tag record.

The detail that makes it sleep rather than loafing is that the animals did not respond to an approaching vessel until physically contacted. That is a genuinely reduced state of awareness. It is also notable against the dolphin comparison, where sleep is famously half-brained: the evidence here is at least consistent with sperm whales shutting down more completely, which would be unusual for a cetacean. No brain activity has been recorded in this species, so it remains an inference from posture and unresponsiveness.

Ambergris is one of the questions people genuinely ask, and the standard answer — whale vomit — is wrong at the level of anatomy. It forms in the rectum, not the stomach, and leaves the way that implies, or is released when a whale that could not pass a large mass dies and decomposes.

Nor is it simply faeces, though it exits with them. It is a concretion built around the sharp, indigestible squid beaks the whale can neither break down nor bring back up — which is a rather good explanation of why an animal eating thousands of beaked cephalopods might need such a thing at all. It occurs in a small minority of whales.

What perfumers value comes later. A mass floating at sea for years oxidises and changes chemically, developing the odour it is famous for; fresh ambergris smells of what it is. Its status in trade varies considerably between countries and is bound up with whale protection law, which is a jurisdictional matter rather than a biological one.

Sperm whales were hunted on a scale hard to picture now, first by open-boat whalers under sail through the nineteenth century and then, far more destructively, by industrial factory fleets in the twentieth. The nineteenth-century phase was for spermaceti, which burned cleaner and brighter than any alternative and lit cities. The twentieth-century phase was for industrial oil, and it killed far more animals in far less time.

The current global estimate is around 360,000 animals, roughly a third of the reconstructed pre-whaling level. Both halves of that need saying together, because conservation coverage usually picks one. Several hundred thousand animals is a large population, and sperm whales are not among the most endangered whales. And they are at a third of what they were, with a reproductive rate — one calf every four to six years, with years of maternal care — that makes a century a short time to recover in.

The estimate itself carries wide uncertainty. Most of the ocean is not surveyed, the global figure is an extrapolation, and historical catch records are incomplete — Soviet whaling in particular was substantially under-reported at the time and has been revised since.

• Do sperm whale codas carry meaning?

  Why it matters: The structural work has mapped a far larger signal space than anyone expected. Whether anything in it refers to anything is the question the whole field now turns on, and it is unanswered.

  What would settle it: Playback experiments showing that a specific coda type reliably produces a specific response, or a coda reliably tied to an independently known referent.

• Do sperm whales sleep with both hemispheres at once?

  Why it matters: Every other cetacean studied sleeps one hemisphere at a time, because breathing is voluntary. If sperm whales do not, they are managing a problem the others have not solved.

  What would settle it: Electrophysiological recording during a resting bout, which no current tag can deliver.

• Why is the spermaceti organ so much larger in males?

  Why it matters: If the organ is purely for echolocation, both sexes need it equally. Substantial dimorphism suggests a second function, possibly in male contests.

  What would settle it: Acoustic recording of male–male interactions with source levels and beam patterns measured.

• Did the removal of older animals during whaling disrupt cultural transmission?

  Why it matters: In a species where repertoire and possibly foraging knowledge are socially learned, killing the oldest animals may have costs that outlast the population loss itself.

  What would settle it: Comparison of repertoire diversity and foraging success between heavily and lightly exploited populations.