Dwarf Sperm Whale (Kogia sima)

Dwarf Sperm Whale
(Kogia sima)
Photo: Robert Pitman, NOAA

Did You Know?

· Similar to squid, dwarf sperm whales use an "ink"-like liquid to evade and deter predators.

· In 1966, a scientist at the Smithsonian Institution in Washington, D.C., determined that the pygmy and dwarf sperm whales were actually two separate species

· Dwarf sperm whales (Kogia sima) were previously known as Kogia simus. The name was changed due to rules in the use of the Latin language.

Status
MMPA - Dwarf sperm whales, like all marine mammals, are protected under the MMPA.

Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Kogiidae
Genus: Kogia
Species: sima

Species Description
Dwarf sperm whales are in the family Kogiidae. They can reach lengths of up to about 9 feet (2.7 m) and weigh between 300-600 pounds (135-270 kg). Females may be slightly smaller than males.

This species has a small compact body that tapers near the tail, and has a dorsal fin located midway down the back. The shape of the dorsal fin varies from falcate, or curved, and pointed to triangular depending on the individual. The head is sometimes described as "shark-like" due to a conical pointed snout and a small narrow distinctive underslung lower jaw. On the throat below the jaw may be several short longitudinal grooves or creases. They have up to 3 pairs of teeth in the upper jaw and 7-13 pairs of teeth in the lower jaw. Their "bulging" eyes are dark with a light circular mark above 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, dwarf sperm whales have a "spermaceti organ" and single blowhole situated slightly to the left side of the body. While at the surface, they have a low flat profile appearance due to the level position of the head and back. The flippers are broad, short, and located forward on the body. 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.

They are frequently seen at the surface either alone or in small groups of up to 6-10 animals. These groups can vary based on age and sex, but little else is known about this species' social organization. Dwarf 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" (floating motionless) 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 visually spot 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 (i.e., calm) sea state and weather conditions (e.g., low wind speeds and little or no swells).

The pygmy sperm whale is another species that appears very similar to the dwarf sperm whale. The two species differ slightly in physical size, morphology, and other minor features. In the field, it is very difficult to distinguish between the two species because they can be so easily confused. The geographic distribution and range for these species may overlap in some areas. Both species are poorly known due to the limited availability of information and are considered "rare."

An unusual characteristic that distinguishes dwarf and pygmy sperm whales from other cetacean species is the use of the "squid tactic." In the lower portion of the intestine, there is a sac filled with viscous, dark reddish-brown liquid. A dwarf sperm whale is capable of ejecting over 3 gallons (12 liters) of this liquid when it feels 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 causes a confusing diversion, allowing the whale to escape (Reeves et al. 2002).

There is inconclusive evidence that dwarf sperm whales are capable of diving to at least 1,000 feet (300 m) to reach their food. They also probably use echolocation to search for prey. Their diet consists of cephalopods (e.g., squid and octopus), crustaceans (e.g., shrimp and crabs), and fish. Based on the structure of their lower jaw and analysis of stomach contents, these whales feed on prey on or near the ocean bottom. They may feed in slightly shallower waters than pygmy sperm whales.

Dwarf sperm whales become sexually mature at 2.5-5 years of age, or about when they reach lengths of 7 feet (2 m). Gestation is estimated to be 9-11 months. In the Southern Hemisphere, birthing may occur in summer from December-March. Newborn calves are about 3.3 feet (1 m) in length and weigh 88-110 pounds (40-50 kg), and are probably weaned after a year when they are larger than 5 feet (1.5 m). Females may give birth to calves in consecutive years. The estimated lifespan for this species may be up to 22 years.

Habitat
Dwarf sperm whales prefer warm tropical, subtropical, and temperate waters worldwide. They are most common along the waters of the continental shelf edge and the slope; dwarf sperm whales are thought to be more "coastal" than pygmy sperm whales.

Dwarf Sperm Whale Range Map
(click for larger view PDF)

Distribution
Dwarf sperm whales have a cosmopolitan distribution in temperate and tropical seas worldwide. In the Southern Hemisphere, their range includes waters off of Australia, New Zealand, Indonesia, Chile, southern Brazil, and South Africa. In the Northern Hemisphere, their range includes Oman, Persian Gulf, the Maldives, Japan, British Columbia, California, Gulf of California, Gulf of Mexico, southeastern U.S. and northwestern Europe (Shirihai and Jarrett 2006). Kogia spp. may be more common off the coasts of the southeastern U.S. and South Africa as evidenced by the higher number of stranding events that have occurred in those areas. Around the Hawaiian Islands, dwarf sperm whales are the sixth most commonly sighted odontocete, or toothed whale. The seasonality and migration patterns of this species are unknown. Much of the information on distribution and biology is based upon stranding records for this species.

Population Trends
For management purposes, dwarf sperm whales inhabiting U.S. waters have been divided into four stocks: California/Oregon/Washington Stock, Hawaiian Stock, Northern Gulf of Mexico Stock, and Western North Atlantic Stock. The estimated abundance for Kogia sp. (dwarf and pygmy sperm whales) is about 300-400 animals for the Western North Atlantic stock, and 600-750 for the Northern Gulf of Mexico stock. The estimated abundance for dwarf sperm whales in the Hawaiian Islands Exclusive Economic Zone (EEZ) is 11,000-19,000. No population size estimate exists for the California/Oregon/Washington stock. In the eastern tropical Pacific there is an estimated 11,000 animals. There are insufficient data for this species to determine the population trends.

Threats
Dwarf sperm whales are entangled, incidentally taken, and/or interact with a number of fisheries, including drift gillnets. This species was occasionally killed by hunters targeting sperm whales during the 19th century and has been recently "taken" in commercial harpoon and drive fisheries in Indonesia, the Lesser Antilles, and Japan (Jefferson et al. 2008). Due to their coastal and nearshore distribution, dwarf sperm whales may be susceptible to human activities and pollution. Their behavior of logging motionless on the sea surface makes them vulnerable to ship strikes. Marine debris may also pose a threat to this species. Evidence from stranded animals shows some dwarf sperm whales have ingested plastic and other garbage, which blocked their intestinal tracks (Reeves et al. 2002). Stranded specimens have had degenerative heart disease, immune system problems, and heavy parasite infestations. Underwater sounds and anthropogenic noise may be harmful to this species of deep-diving whales.

Conservation Efforts
The IUCN Red List of Threatened Species considers this species "Lower Risk/Least Concern."

Regulatory Overview
This species is protected under the Marine Mammal Protection Act of 1972 as amended.

Key Documents
(All documents are in PDF format.)

Title	Federal Register	Date
Stock Assessment Reports	n/a	various

More Information

References:

Reeves, R. R., P. A. Folkens, et al. (2002). Guide to Marine Mammals of the World. New York, Alfred A. Knopf. p. 244-247.
Jefferson, T. A, M. A. Webber, and R. L. Pitman. (2008). Marine Mammals of the World, A Comprehensive Guide to their Identification. Amsterdam, Elsevier. p. 82-84.
Shirihai, H. and B. Jarrett (2006). Whales, Dolphins and Other Marine Mammals of the World. Princeton, Princeton University Press. p.150-152.