Linnaeus, 1758 - Sperm whale
The largest toothed cetacean, the sperm whale, is unlikely to be confused with any other species. The body is somewhat laterally compressed and the head is huge (one-quarter to one-third of the total length, and an even greater proportion of the total bulk) and squarish when viewed from the side. The lower jaw is narrow and underslung. The single S-shaped blowhole is set at the front of the head and is offset to the left. The flippers are wide and spatulate, and the flukes are broad and triangular with a nearly straight trailing edge, rounded tips, and a deep notch. There is a low rounded dorsal hump and a series of bumps, or crenulations, on the dorsal ridge of the tail stock. The body surface tends to be wrinkled behind the head.
Sperm whales are predominantly black to brownish grey, with white areas around the mouth and often on the belly. Functional teeth (18 to 25 pairs that fit into sockets in the upper jaw) are present in the lower jaw only. The bushy blow projects up to 5 m and, because of the position of the blowhole, is directed forward and to the left. On windless days, such an angled blow is diagnostic.
Adult males and females can be distinguished not only by size differences, but also by the presence or absence of calluses on the dorsal hump. A large percentage of females (about 85%) have calluses, whereas males almost never have them.
Can be confused with
Sperm whales are generally easy to distinguish from other large whales at sea, even at a great distance. The uniquely angled blow is diagnostic, but one must be careful to take into account the effects of wind on a whale's blow. Only humpbacks, and possibly gray whales, would likely confused with sperm whales, and this only at a great distance.
Newborn sperm whales are 3.5 to 4.5 m long. Adult females are up to 12 m and adult males are up to 18 m in length. Weights of up to 57 t have been recorded.
Sperm whales are distributed from the tropics to the pack-ice edges in both hemispheres, although generally only large males venture to the extreme northern and southern portions of the range (poleward of 40° latitude). Deep divers, sperm whales tend to inhabit oceanic waters, but they do come close to shore where submarine canyons or other physical features bring deep water near the coast.
Biology and Behaviour
Although bulls are sometimes seen singly (especially above 40° latitude), sperm whales are more often found in medium to large groups of up to fifty whales. Recently, the social system of sperm whales has been relatively well-studied. Apparently they are polygynous; adult males seem to employ a “searching” strategy for mating, associating with nursery groups of adult females and their offspring for only short periods of time. Sexually mature but non-breeding males that have been displaced from their maternal pods form bachelor herds. Most births occur in summer and autumn. Sperm whales are deep divers, apparently capable of reaching depths of 3200 m or more. Some dives of bulls, which are longer than those of the smaller cows, last at least 2 hours. Fluking-up is common before a long dive. Low-frequency, stereotyped, clicked vocalizations, some of which are termed “codas,” are apparently distinct to individual sperm whales and may act as acoustic signatures. Some clicks are also probably used in echolocation. An amazing variety of fish, cephalopods, and non-food items has been found in the stomachs of sperm whales from around the world. Cephalopods (squid and octopuses), however, are considered to be the major prey items.
Sperm whaling has a long history. The most intense periods were the “yankee whaling” era of the 1800s and the factory ship whaling of the 20th century. Recent findings of studies on social behaviour and breeding undermine assumptions in the models on which exploitation and management have long been based. Certain populations have been depleted, but the sperm whale remains the most abundant of all the great whales (Great whales generally include the sperm whale and all baleen whales, except the pygmy right whale).