Pygmy sperm whales and their close relatives the dwarf sperm whales have similarities to the great sperm whale after which they are named. However, they are classified into a different family. Like the sperm whales, the pygmy sperm whale has teeth in the lower jaw only (the dwarf sperm whale has up to three pairs of teeth in the upper jaw). This species is not very well studied.
This species has a small, compact body that tapers near the tail and has a small, low, rounded, “dorsal” fin. The shape of the dorsal fin varies depending on the individual. The head is sometime described as “shark-like” due to a conical, pointed snout, and a small narrow, distinctive, underslung lower jaw. Unlike dwarf sperm whales, this species does not have irregular grooves or creases on the throat. Pygmy sperm whales lack teeth in their upper jaw, but have 10-16 pairs of teeth in the lower jaw that fit into sockets in the upper jaw. Their “bulging” eyes are dark with a light circular mark above and around them. Behind the eye is a pale false gill plate, which looks similar to a fish’s gill cover. Like their larger cousin the sperm whale, pygmy sperm whales have a “spermaceti” organ and single blowhole situated slightly to the left side of the body. While on the surface, they have a low profile due to the level position of the head and back. The skin is wrinkled (only when closely observed) and has a brownish to dark bluish-gray coloration on the dorsal side. The ventral side is paler with whitish to pinkish coloration that gives the animal a counter-shading effect.
Its body is blue-gray to black above, shading to light gray on the sides and soft white to pink on the belly.
FINS AND FLUKES
Its flippers are located behind and below the “false gill” and are large and slightly rounded at the tips. A very small, curved dorsal fin is located behind the midsection. The flukes are almost dolphin-like with a deep notch in the center.
LENGTH AND WEIGHT
Length averages 10 feet (3 m) for both sexes. Maximum length of adults is 16 feet (4.8 m). Weight can reach 700 to 1,000 (315 to 450 kg).
Pygmy sperm whales are probably capable of diving to at least 1,000 ft (300 m) in search of food. They use echolocation to locate prey. Their diet consists of cephalopods (e.g., squid and octopus), crustaceans (e.g., crabs and shrimp), and fish. Based on the structure of their lower jaw and analysis of stomach contents, these animals forage and feed in mostly mid and deep water environments, as well as near the ocean bottom.
MATING AND BREEDING
Pygmy sperm whales become sexually mature at 4-5 years of age. Gestation in these cetaceans is about 9-11 months. The mating and calving season lasts about nine months, and peaks from March-August in the Northern Hemisphere. Newborn calves are about 4 feet (1.2 m) in length and weigh 110 pounds (50 kg), and are probably weaned after a year. Females may also give birth to a calf in consecutive years. The estimated lifespan for this species may be up to 23 years.
DISTRIBUTION AND MIGRATION
Pygmy sperm whales have a cosmopolitan distribution in temperate and tropical seas worldwide. They are most common along the waters seaward of the continental shelf edge and the slope.
In the Southern Hemisphere, their range includes Chile, South Africa, the Tasman Sea, and Uruguay. In the Northern Hemisphere, their range includes the Netherlands, northwestern Europe, the Azores, Nova Scotia, Washington, Hawaii, and Japan.
Kogia (the genus that both pygmy and dwarf sperm whales belong to) may be more common off the coasts of the southeastern United States and South Africa based on the records of higher numbers of “stranding events” in these areas. The seasonality and migration patterns of this species are unknown.
Pygmy sperm whales are frequently seen at the surface either alone or in small groups of up to 6-7 animals. Group composition can vary/mix based on age and sex, but little else is known about their social organization. Pygmy sperm whales are rarely active or aerial at the surface, and it is very uncommon for them to approach boats. Usually they are seen slowly swimming (3 knots) or “logging” at the surface, showing only a small portion of their body. Before diving, they will
slowly roll or sink and disappear from view without displaying their flukes.
This species is very difficult to observe at sea given their timid behavior, lack of a visible blow, and low profile/appearance in the water. They are usually only detected in ideal sea state (calm) and weather conditions (low wind speeds and little or no swells).
Strandings are common to this species, especially in some areas of southeast coast of the United States, and often they strand alive either as single individuals or cow calf pairs. Many have been taken to aquariums where all efforts to keep them alive have been unsuccessful.
An unusual characteristic that distinguishes pygmy and dwarf sperm whales from other cetacean species is the use of the “squid tactic.” In the lower portion of the intestine, each species has a sac filled with liquid. These animals are capable of ejecting over 3 gallons (12 liters) of viscous, dark reddish-brown liquid when they feel threatened or when trying to evade predators. Similar to squid and other cephalopod species, the “ink” creates a dense cloud that may discourage predators and/or functions as a confusing diversion allowing the whale to escape.
The species is not listed as threatened or endangered under the Endangered Species Act. These animals are exposed to by-catch in fishing gear that includes driftnets, gill-nets and purse seine operations, commercial harpoon fisheries in Indonesia, the Lesser Antilles, and Japan, ship strikes, and occasionally marine debris.
Some stranded whales have been documented with plastics and other garbage blocking their guts. Other threats include underwater sounds and anthropogenic noise. Anthropogenic noise levels in the world’s oceans are an increasing habitat concern, particularly for deep-diving cetaceans like pygmy sperm whales that use sound to feed, communicate, and navigate in the ocean.
BIBLIOGRAPHY: For further details about common dolphins you may want to consult the following literature:
• Marine Mammals of the World. A Comprehensive Guide to their Identification. Jefferson, et al. 2008. Elsevier. p. 79-81.
• Guide to Marine Mammals of the World. Reeves et al., 2002. Knopf. p. 244-247.
• Whales, Dolphins and Other Marine Mammals of the World. Shirihai, H. and B. Jarrett (2006). Princeton, Princeton University Press. p.148-150.
ACKNOWLEDGMENTS: The information contained in this document was gathered from various sources, including NOAA, ACS and our own publications.