Scientific name: Physeter macrocephalus
Scientific classification:
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Physerteridae
What does it look like? The sperm whale is the largest of the toothed whales. Males (bulls) can be as long as 20 m and weigh 70 tonnes. Females are much smaller. Th e whale has a huge block head, small pectoral fins, a large triangular tail fluke and a long, narrow lower-jaw studded with large conical teeth. Where does it live? Sperm whales are found throughout the world’s oceans and in the Mediterranean Sea. Populations are most dense in regions above underwater continental shelves and canyons.
Plumbing the Depths
Th e head of the sperm whale is immense, accounting for 40 percent of its total body length. If this capacious space was filled with brain, the sperm whale would have more grey matter than it knew what to do with, alas, the rectangular head is filled mostly with wax. Th is wax is whitish and rather gloopy, giving the whale its common name as whalers in the eighteenth and nineteenth centuries likened it to semen.
Why should this animal have a head brimming with wax? Th e blunt answer is that no one is really sure. Th ere are several theories. One of these relates to the whale’s feeding behavior. Th e favored prey of the sperm whale are those animals that dwell on or near the seabed, such as squid, fish, and small sharks. To reach these tasty morsels, the whale must dive to great depths, making it the deepest-diving animal on the planet. It is not known exactly how deep they can dive, but it is at least 1,200 m and possibly as much as 3,200 m (about 10 times the height of the Eiffel tower). These dives can last for two hours. Th e whales don’t have an aqualung; however, their muscles can store a lot of oxygen, enabling them to stay underwater for long periods. Even so, swimming down to the seabed would quickly drain their oxygen stores, so it is has been proposed that the wax aids them in their search for food.
The wax organ in the head, the spermaceti organ, has a series of passages and chambers and a blood supply. When the sperm whale is ready to dive, some scientists have suggested that seawater is allowed into these passages, circulating around the wax and cooling it. Cooling results in shrinkage, and the wax increases in density, surpassing that of the surrounding seawater. With a heavy head, the whale sinks to the bottom at a rate of around 170 m per minute. Once at the bottom, the whale can begin to feed. After a good forage, hunting for nameless creatures in inky blackness, the whale’s oxygen stores begin to run low. Th e whale must return to the surface or drown. It has been theorized that blood fl ow is increased to the wax organ, and as it warms, it expands,becoming lighter and acting like a buoyancy aid to carry the exhausted whale back to the surface. Once at the surface, the animal rests for approximately five minutes before diving again. After several long dives, the whale is thoroughly spent and has to fl oat around on the surface for many minutes.
The buoyancy aid theory is an interesting one, but it has also been suggested the spermacetiorgan helps the whale catch its prey in the pitch dark of the ocean depths. It is possible they just reach the seabed and scoop up the bottom mud and anything edible. Tin cans and stones in the stomach of captured whales support this notion, but more interesting is the fact that, like bats, sperm whales can echolocate, using sound to build up a picture of their environment. Echolocation may be used not only to find their prey but also as a weapon. It is thought the sound pulses produced by the whale are focused by the wax in the spermacetiorgan, in much the same way as a glass lens focuses light. Th e focused bursts of sound produce pressure waves in the water that stun prey.
The large wax-filled head of the whale may also be important during the breeding season. Some scientists think the head full of wax acts as a shock absorber to prevent damage to the delicate parts of the head when the animals ram into each other during disputes, or even into ships when defending themselves. In the whaling days, three whaling ships are known to have been sunk after being rammed by large sperm whales. Th is may explain the wax, but the female also has a wax-filled head, and fighting is normally the pastime of male mammals. Also, some other species of cetaceans have wax in their heads, such as the bottlenosed whales. They are not known to ram into one another, but they do dive to great depths to capture squid, supporting the theory that the wax is somehow involved in feeding.
• Th e sperm whale holds other records in the animal kingdom. In addition to being the deepest diving animal, it also has the largest brain, weighing in at 9 kg. In comparison, a human brain weighs 1–1.5 kg. It is also thought to be the largest toothed animal that has ever lived. There is evidence of giant bulls killed in the early days of whaling, which were probably 28 m long and 150 tonnes in weight. If these accolades weren’t enough, the sperm whale also has the thickest skin of any animal more than 30 cm!
• The title role of Herman Melville’s classic, Moby Dick, was a gigantic white sperm whale.
• This species was once the favored target for whalers, as the whales rest at the surface for a long time, completely exhausted after finishing a sequence of long dives and are therefore essentially defenseless. Th e whalers used hand harpoons and later shipmounted ones to kill the whales, before dragging them back to the ship. Its social behavior also made it attractive to whalers. Pods of this cetacean consist of females and young males (adult males are solitary), and if one member of the family is injured, the whales will rally around and support the injured animal (the marguerite formation) to prevent it from drowning. Th is behavior made it easy for whalers to kill many individuals quickly, as other group members would soon surround an injured animal.
• Once dead, the whales were not only processed for their meat and blubber, but also for the spermaceti wax in the head, which was used as a high quality lubricant. Up until recently it was used as a lubricant in some very high-tech applications, such as the space industry, where synthetic alternatives could not match its specific qualities. Another substance, found in the intestine of the sperm whale, ambergris, is also highly prized. It is thought this substance, also known as so-called floating gold binds hard, indigestible bits of food so they can be safely passed from the whale’s digestive system. Fresh ambergris is black and sticky and is far from sweet smelling. Once passed by
the whale it can drift for many years, all the time being weathered by the sun and salt water. Eventually, when it gets washed up, its smell has become a lot more alluring. It is this weathered ambergris that is prized by purveyors of fi ne fragrances, commanding prices of $20 per gram. A 15 kg lump recently found washed up in southern Australia would be worth $295,000, which is a good reason to take up beachcombing.
• The sperm whale was hunted ruthlessly in the 1850s to the point where the population collapsed in 1860. Th e population recovered, and in the 1960s, when factory ships scoured the oceans vacuuming up the large whales, at least 25,000 sperm whales were killed every year. Th e peak was in the 1963–64 season when 29,300 animals were taken. Th is scale of exploitation is not sustainable, and the commercial hunting of these whales is banned; fortunately only Norway, Japan, and some indigenous peoples are allowed to catch a small quota.
