Sperm whale

Habitat: Mainly offshore, either in mid ocean or over submarine canyons at edges of continental shelf or beyond. Can occur close to coasts of volcanic and oceanic islands in waters >200 m deep.

Description: Dark grey, paler patches on genital area, inside of mouth and skin on upper and lower jaws cream or white. Most striking feature is huge, barrel-shaped head, up to 1/3 of body length in males. Lower jaw is narrow, long, stops before end of snout. Scarring (from other sperm whales and squid) common especially in mature males. Short, ill-defined throat grooved. Flippers are large, rounded, paddle-like. Small dorsal fin, often topped by white-ish callus, especially in mature females; often, several pronounced bumps run along spine to deeply notched triangular flukes. Flukes are plain and uniform in colouration. Lower jaw holds 20 – 26 pairs of large peg-like teeth, which fit into matching sockets in upper jaw. Head contains spermaceti organ and junk organ (also containing spermaceti chambers) thought to be involved in sound production and buoyancy.

Size: Females 11 m, rarely to 12.5 m; males 15.8 m, rarely to 18.5 m. Large bulls have become rarer after selection by whalers.

Weight: 13,500 kg (females), 44,000 kg (males).

Lifespan: Estimated 65 – 70 years.

Distribution: Worldwide in deep waters. Females and juvenile males have a more limited range than adolescent and mature males, being mainly confined to warmer waters with sea surface temperatures >15° C, between 45° N and 45° S. Only large males found in highest latitudes, generally in productive deep waters. There have been no systematic surveys for sperm whale in British and Irish waters. Generally only males come as far north as British Isles, although smaller individuals sometimes noted, virtually all sightings come from deep waters off continental shelf. Relatively high densities around Rockall to north of Outer Hebrides, north and west of Shetland in Faroe-Shetland Channel, and in Bay of Biscay. Sightings around Britain and Ireland generally July – December, but increasing evidence of small groups remaining at high latitudes into winter.

Diet and feeding: Varied diet but mainly mesopelagic squid. Males take larger items than females and more likely to eat demersal fish. In some areas, such as Iceland, deep-living fish are dominant prey.

Breeding: Poorly understood. Mating probably takes place in February – June in north Atlantic. Births occur in June – September. Gestation lasts for 16 – 17 months, lactation at least 19 – 42 months (some young continue to take milk for 13 years, may be a comfort behaviour), calving interval 3 – 15 years. Sexual maturity reached at 18 – 19 years in males, 7 – 12 in females, although males do not typically mate before their late 20s. Physical maturity not reached until around 30 years in females and 50 years in males.

Conservation status and population: Listed by IUCN as vulnerable. No reliable estimates for global or North Atlantic population, but probably a few hundred thousand globally. Once a common animal but reduced substantially by historically devastating levels of whaling worldwide; in North Atlantic along, >20,000 taken since 1950. Numbers now recovering, but at an unknown rate. Young sperm whales sometimes caught in drift nets, set nets, may be victims of ship strikes. Some killed by plastic ingestion. Contaminant levels usually somewhat higher than in baleen whales. Relatively high cadmium levels probably natural.

Identification

Distinguished at sea by single blowhole at apex of head, left of centre, producing low (1.5 – 5 m), bushy, forward-left facing blow. Head is dark, smooth, disproportionately large. Usually raises large, triangular flukes above surface when diving. Flukes are plain, unlike humpback whale.

Vocalisations: Very vocal but only makes short, impulsive, broadband (0.1 – 30 kHz) click-type vocalisations. Long, regular click sequences (2/s during deep dives) probably used for echolocation. Stereotyped patterns of clicks (3 to 20 clicks lasting 0.2 – 2 s), called ‘codas’, heard from socialising female groups and may be important for communication. Groups of females have distinctive coda repertoires, probably acquired culturally. Slow, ringing clicks or clangs repeated every 6 – 8s are produced almost entirely by large males, function unclear. Accelerating series of clicks called ‘creaks’ are thought to represent foraging attempts. Typically quiet at surface unless socialising.