The dwarf sperm whale is a toothed whale named after the waxy substance, spermaceti, found in its head. This organ is a sac of oil that helps the whales produce sound. Similar to squids, dwarf sperm whales can produce a dark, ink-like liquid that helps them escape from predators.
Dwarf sperm whales are found in temperate and tropical seas worldwide. The dwarf sperm whale appears very similar to the pygmy sperm whale. In the field, it is very difficult to distinguish between the two species because they can be so easily confused. Both species are poorly known due to the limited availability of information and their cryptic appearance at sea.
The dwarf sperm whale can range in size from 2 to 2.7 m (6.6 to 8.9 ft) in length and 136 to 272 kg (300 to 600 lb) in weight—less than the 4.25 m (14 ft) and 417 kg (920 lb) pygmy sperm whale. A newborn is generally around 1 m (3 ft 3 in) long and 14 kg (31 lb). Males are thought to reach physical maturity at age 15, and females at age 13. Sexual maturity, which happens after an individual has attained 2–2.2 m (6 ft 7 in–7 ft 3 in) in length, happens at 2 to 3 years for males and around 5 for females.
Gestation takes place probably over around 9.5 months.
The dwarf sperm whale has a dark-gray or blue-gray coloration with a lighter-gray underside, and a pale, crescent-shaped mark between the eye and the flipper, sometimes called a “fake gill,” which is characteristic of the genus. Some individuals have been known to have a second crescent-shaped mark, creating a sort of pale ring encircling a darker spot. It has a high dorsal fin halfway down the length of the body, and two or more throat grooves. The dorsal fin is taller and closer to the head than it is in the pygmy sperm whale, and the back is flatter.
Population and distribution
The dwarf sperm whale ranges throughout tropical and temperate oceans of the world and inhabits the continental shelf and slope area. It seems to prefer warmer waters than the pygmy sperm whale. The dwarf sperm whale is one of the most commonly beached deep-diving whales in the world, though rarely seen at sea, and likewise, most information about the whale comes from examining beached individuals. Diving depth may vary from place to place: a study in the Bahamas placed average depth at around 250 m (820 ft), whereas a study in the deeper waters of Hawaii placed it at around 1,500 m (4,900 ft).
In the West Pacific, its recorded range spans from Japan to Tasmania and New Zealand, and in the East Pacific from British Columbia to central Chile. In the Indian Ocean, the whale is reported from Oman, Sri Lanka, India, Thailand, Philippines, Indonesia around Timor, western Australia and South Africa. In the West Atlantic, it has been recorded from Virginia to southern Brazil, and in the East Atlantic from Italy in the Mediterranean Sea to South Africa.
Lifespan & Reproduction
Dwarf sperm whales can live up to 22 years. They reach sexual maturity when they are 2.5 to 5 years old. In the Southern Hemisphere, females give birth between December and March. Females may give birth after a pregnancy that lasts about 1 year. Calves are about 3.3 feet long and weigh about 30 pounds at birth. They are weaned after 1 year.
Behavior and Diet
Dwarf sperm whales are usually seen either alone or in small groups of 16 or fewer individuals. These groups can vary based on age and sex, but little else is known about their social organization.
Dwarf sperm whales spend very little time at the water’s surface and almost never approach vessels. When they are seen at the surface, they are usually either swimming slowly or lying still (also known as logging). Their blows are not visible when they surface. They will slowly sink and disappear from view without showing their flukes before diving back into the water.
Dwarf sperm whales’ use of the “squid tactic” makes them unique among whales. Each dwarf sperm whale has a sac filled with dark liquid in its intestine. The whale can release more than three gallons of dark, reddish-brown liquid—or ink—from this sac. This liquid creates a dark cloud in the water to help protect the whales when they feel threatened or when they are trying to escape predators.
Dwarf sperm whales can dive at least 1,000 feet deep in search of food. They may feed in slightly shallower waters than pygmy sperm whales. They eat cephalopods (e.g., squid and octopus), crustaceans (e.g., crabs and shrimp), and fish. Like bats, and other toothed whales, dwarf sperm whales use echolocation to locate prey, meaning they use sound to navigate and “see” the world around them. They do so by producing sounds from their melons (or foreheads) that reflect off of the objects around them.