Sperm whales are the largest toothed predators on Earth, and their menu is dominated by squid that live far below the sunlit surface.1Deep-Sea Research Part I: Oceanographic Research Papers. A taste for squid: the diet of sperm whales stranded in Greece, Eastern Mediterranean The famous image of a whale wrestling a giant squid tells only a small part of the story, since most meals are far more modest. These whales hunt in near-total darkness, relying on sound rather than sight to find each one.
Squid Make Up Most of the Menu
Across most regions examined, sperm whales feed mainly on squid and their relatives, such as octopuses, living roughly 200 to 4,000 meters down.2Deep-Sea Research Part I: Oceanographic Research Papers. A taste for squid: the diet of sperm whales stranded in Greece, Eastern Mediterranean A typical prey squid looks nothing like the monster in the movies. Most are about arm-length or smaller, and many, like the jewel squid, carry light-producing organs that they use in the dark. A whale that size needs a huge amount of fuel every day, so it is the sheer quantity of modest squid that matters, not the rare giant.
A detailed look at whales stranded in Greece shows how concentrated a diet can be. Their remains contained more than 48,000 prey pieces from 18 species, 17 of them cephalopods and just one fish.3Elsevier (Deep Sea Research Part I: Oceanographic Research Papers). A taste for squid: the diet of sperm whales stranded in Greece, Eastern Mediterranean Fifteen of those species were deep-sea squid that no fishery targets, so these whales were not competing with people for food.4Elsevier (Deep Sea Research Part I: Oceanographic Research Papers). A taste for squid: the diet of sperm whales stranded in Greece, Eastern Mediterranean
One jewel squid species made up nearly half the prey by number and two-thirds by weight.5Elsevier (Deep Sea Research Part I: Oceanographic Research Papers). A taste for squid: the diet of sperm whales stranded in Greece, Eastern Mediterranean Another whale, stranded south of Crete, held almost nothing but squid beaks, about 3,900 of them, from seven species people rarely catch.6Journal of the Marine Biological Association of the United Kingdom. Examination of the stomach contents from a Mediterranean sperm whale found south of Crete, Greece The same few species keep turning up because a whale’s diet reflects what is abundant in the depth band where it hunts.
Scientists can work out what was eaten even though squid bodies dissolve. The hard beaks resist digestion and pile up in the stomach long after the soft parts are gone. Beak shape differs by species, so researchers match each one to a reference collection. Each squid has one beak, so counting them shows how many were eaten, and beak size scales with body size, which lets researchers estimate how heavy each squid was.
Young whales eat smaller versions of the same prey. Calves ate smaller squid of the same three main species as older whales,7Elsevier (Deep Sea Research Part I: Oceanographic Research Papers). A taste for squid: the diet of sperm whales stranded in Greece, Eastern Mediterranean probably because larger squid are harder for a young whale to catch.8Elsevier (Deep Sea Research Part I: Oceanographic Research Papers). A taste for squid: the diet of sperm whales stranded in Greece, Eastern Mediterranean
The Truth About Giant and Colossal Squid
Sucker-shaped scars on some sperm whales’ skin have fueled images of epic battles with giant squid.9Biology Letters. What the stomach contents of sperm whales tell us about giant squid and octopuses But to learn what whales actually eat, researchers rely on the hard, parrot-like beaks that survive in the stomach.10Biology Letters. What the stomach contents of sperm whales tell us about giant squid and octopuses
A “battle” probably looks less like a duel than a catch. The scars come from squid suckers and hooks as the whale seizes its prey, and the squid is fighting to escape, not attacking. No one has filmed a full fight in the deep. Round sucker scars show contact with a squid, but not who started the encounter or whether the squid was a giant, and they fade over time, so what is visible may be only the deeper or more recent marks.
Giant squid are widespread but live thinly spread through the deep, so a whale cannot count on finding one on every dive. It gets more food, more reliably, from the denser schools of mid-sized squid. Giant squid beaks in a stomach prove a whale ate one, but not that giants were a major share of its diet.
The colossal squid is a different story. The giant squid is longer, while the colossal squid is heavier, and it lives in the cold Southern Ocean. Around Antarctica, sperm whales appear to be the only major predator of healthy adult colossal squid,11Deep-Sea Research Part I: Oceanographic Research Papers. Distribution and biology of the colossal squid, Mesonychoteuthis hamiltoni: New data from depredation in toothfish fisheries and sperm whale stomach contents and they are estimated to eat around 9 million tons of colossal squid a year.12Deep-Sea Research Part I: Oceanographic Research Papers. Distribution and biology of the colossal squid, Mesonychoteuthis hamiltoni: New data from depredation in toothfish fisheries and sperm whale stomach contents
How Deep They Dive and How They Find Food by Sound
A typical feeding dive lasts about 45 minutes, followed by around 9 minutes resting at the surface.13PubMed. Deep-diving foraging behaviour of sperm whales (Physeter macrocephalus) That means whales spend more than 72% of their time in these feeding dive cycles.14PubMed. Deep-diving foraging behaviour of sperm whales (Physeter macrocephalus) Average maximum depths range from about 650 to 1,000 meters depending on region,15PubMed. Deep-diving foraging behaviour of sperm whales (Physeter macrocephalus) but dives as deep as 1,500 meters happen, and some whales stay down 75 minutes.16PubMed Central. Sperm whale dive behavior characteristics derived from intermediate‐duration archival tag data
Sunlight fades away within a few hundred meters, so sight is little use. Sound travels far and fast underwater, and echoes reveal the size and distance of an object in total darkness. Sperm whales find prey by sound. While diving, they send out regular clicks every half second to two seconds and listen for the echoes.
Close to prey, they switch to a rapid buzz, which researchers call a creak.17PubMed Central. Sperm whale behaviour indicates the use of echolocation click buzzes “creaks” in prey capture Faster clicks give a constant stream of updates on where the prey is during the final chase.18PubMed Central. Sperm whale predator-prey interactions involve chasing and buzzing, but no acoustic stunning The whales also turn their clicks down sharply during the buzz, similar to dolphins.19PubMed Central. Sperm whale predator-prey interactions involve chasing and buzzing, but no acoustic stunning Almost all creaks happen in the deepest half of dives, where whales twist and turn chasing prey.20PubMed Central. Sperm whale behaviour indicates the use of echolocation click buzzes “creaks” in prey capture They tend to hunt in one or two depth bands, which suggests prey gather in layers.21PubMed Central. Sperm whale behaviour indicates the use of echolocation click buzzes “creaks” in prey capture
Researchers listen with underwater microphones or tags, and a change from steady clicks to a rapid creak marks an attempt to catch prey. Counting creaks gives a rough measure of how often a whale tries to feed. A creak shows an attempt, not a catch, so a dive with many creaks does not guarantee many meals.
An old idea held that sperm whales stun prey with loud clicks. But tagged whales chased and buzzed prey with no sign of stunning.22PubMed Central. Sperm whale predator-prey interactions involve chasing and buzzing, but no acoustic stunning
Eating by Suction Instead of Biting
Unlike dolphins, a sperm whale has a short, wide tongue set at the back of the mouth, far from its teeth.23Aquatic Mammals. Functional Morphology of the Sperm Whale (Physeter macrocephalus) Tongue, with Reference to Suction Feeding The tongue can’t easily handle grabbed prey, but it is pulled backward like a piston to create suction that draws prey in.24Aquatic Mammals. Functional Morphology of the Sperm Whale (Physeter macrocephalus) Tongue, with Reference to Suction Feeding
Teeth sit only on the lower jaw. The upper teeth are absent or never break through the gum, and the lower teeth fit into sockets in the upper jaw.
The whale opens its lower jaw and pulls its tongue back, which lowers the pressure in its mouth and draws in water and prey together. A quick strike from close range suits a whale that has already located the squid by sound. Soft squid are easy to swallow whole, and since prey isn’t chewed, the beaks arrive intact in the stomach. Sharp squid beaks in the gut may be wrapped in a waxy mass that becomes ambergris, possibly protecting the intestines.25Harbor Breeze Cruises. 10 Facts About Ambergris
Their ancestors were biters. Fossil sperm whales had teeth in both jaws and hunted more like killer whales.26Journal of Vertebrate Paleontology. Living fast and dying young: life history and ecology of a Neogene sperm whale Over millions of years, the lineage shifted toward deep diving and suction feeding.27Encyclopedia of Marine Mammals. Sperm and Beaked Whales, Evolution
When Sperm Whales Eat Fish
Whales prey on fish where fish are plentiful at their hunting depth. In the Gulf of Alaska, they ate mostly sablefish, dogfish, skates and rockfish.28PubMed Central. Exploring variability in the diet of depredating sperm whales in the Gulf of Alaska through stable isotope analysis Whales that often visited fishing boats ate even more skates, about half their diet.29PubMed Central. Exploring variability in the diet of depredating sperm whales in the Gulf of Alaska through stable isotope analysis Fishing gear in the water makes certain fish, such as sablefish, an easier and more concentrated meal than usual.
Sperm whales also steal fish, pulling them off longlines as the gear is hauled up.30Marine Mammal Science. Sperm whale depredation of sablefish longline gear in the northeast Pacific Ocean Hooked fish are an easy, concentrated meal that saves diving effort, and the habit can spread among whales in an area.
In Alaska, whales showed up on 16% of survey days and took fish in 65% of those sightings.31Marine Mammal Science. Sperm whale depredation of sablefish longline gear in the northeast Pacific Ocean Even so, they took less than 1% of Alaska’s yearly sablefish catch,32Marine Mammal Science. Sperm whale depredation of sablefish longline gear in the northeast Pacific Ocean so the total loss there is small, even when individual hauls are hit. In the southern Indian Ocean the picture is harsher: they struck up to 61% of toothfish lines, costing thousands of tons of fish.33Fisheries Research. How do fishing practices influence sperm whale (Physeter macrocephalus) depredation on demersal longline fisheries?
Diet Changes with Sex, Family Group and Place
Young males leave their family groups around age ten and move toward colder waters.34Journal of the Marine Biological Association of the United Kingdom. Stable isotope profiles in sperm whale teeth: variations between areas and sexes Females and young stay in warmer waters, while big males roam as far as polar seas, where they meet prey like colossal squid that females rarely do. Even in the small Mediterranean population, males and females feed on different prey and habitats,35Marine Ecology Progress Series. Stable isotopes suggest fine-scale sexual segregation in an isolated, endangered sperm whale population which may reduce competition between the sexes.36Marine Ecology Progress Series. Stable isotopes suggest fine-scale sexual segregation in an isolated, endangered sperm whale population Individual males in New Zealand varied in diet by season.37Marine Ecology Progress Series. Stable isotope analyses reveal seasonal and inter-individual variation in the foraging ecology of sperm whales
Family clans have their own tastes too. Clans with distinct click “dialects” show different diets, likely because they use different parts of the ocean.38Marine Ecology Progress Series. Sperm whale diet variation by sex, location, year, social group and clan: Evidence from stable isotopes
Scientists can read diet without harming whales. Chemical traces in skin reflect recent meals, and growth layers in teeth record diet over a lifetime.
Plastic, Shifting Prey and Other Threats to Their Food
Two male sperm whales stranded in California had swallowed 134 kinds of floating net, and gut blockages likely killed both.39PubMed. Fatal ingestion of floating net debris by two sperm whales (Physeter macrocephalus) A Mediterranean whale died of a ruptured stomach packed with plastic.40PubMed. As main meal for sperm whales: plastics debris Of 22 whales stranded on North Sea coasts in 2016, nine held nets, rope, packaging and even a car part.41PubMed. Large amounts of marine debris found in sperm whales stranded along the North Sea coast in early 2016
Suction pulls in whatever floats near the prey, and nets drift into feeding areas. A whale’s stomach can’t pass large material. Netting and rope tangle into a mass that can block the digestive system. Because much of the debris is fishing gear, lost nets and lines are a particular worry, and keeping fishing gear and plastic out of the sea helps.
Prey can also vanish. Sperm whales left the central Gulf of California between 2016 and 2018 after jumbo squid declined and shrank.42PubMed Central. The departure of sperm whales (Physeter macrocephalus) in response to the declining jumbo squid (Dosidicus gigas) population in the central portion of the Gulf of California The squid collapse likely followed decades of warming water and a fishery collapse.43PubMed Central. The departure of sperm whales (Physeter macrocephalus) in response to the declining jumbo squid (Dosidicus gigas) population in the central portion of the Gulf of California
How Their Meals Help Fertilize the Ocean
Sperm whales eat in the deep and release iron-rich liquid feces near the sunlit surface.44PubMed Central. Iron defecation by sperm whales stimulates carbon export in the Southern Ocean Southern Ocean waters lack iron, which limits plankton growth. The whales add about 50 tons of iron to those surface waters yearly.45PubMed Central. Iron defecation by sperm whales stimulates carbon export in the Southern Ocean Plankton there use it to bloom, and growing plankton take in carbon dioxide, pulling about 200,000 more tons of carbon from the air than the whales breathe out.46PubMed Central. Iron defecation by sperm whales stimulates carbon export in the Southern Ocean