Kogia sima
dwarf sperm whale

Information on the geographic range of this species is limited due to its rarity. Based on stranding and fishery by-catch records, dwarf sperm whales have a worldwide distribution. Although stranding records show that they occur in areas of cold waters, they are more frequently observed in temperate and tropical regions. In the Atlantic Ocean, dwarf sperm whales have been spotted offshore near Virginia, Spain, Brazil, and along the coasts of Africa. In the Indian Ocean, strandings have occurred along the southern coast of Australia, in the Persian Gulf, and in the Indonesian archipelago. In the western Pacific, strandings have occurred along the shores of the island of Honshu in Japan, the Marianas Islands, and New Zealand. In the eastern Pacific, they range from Vancouver Island, Canada to the central coast of Chile. (Culik, 2010; Eder, 2001; Petrie, 2005)

Dwarf sperm whales are usually seen over the continental shelf and slope. However, dietary evidence suggests that these whales forage in deeper waters, diving to 300 m. (Culik, 2010; Day, 2007; Eder, 2001; Petrie, 2005)

Dwarf sperm whales are compact and streamlined, with the body gradually narrowing to the tail. Average body length ranges between 2.1 to 2.7 m but rarely exceeds 2.5 m. Average body weight ranges from 135 to 270 kg. Skin color varies from bluish gray, dark gray, and blackish brown, to completely black with a white or lighter gray venter; speckled pink or purple blotches may also be present. The flippers are broad with round edges and the tail fluke is sharply pointed, measuring 61 cm in width. The dorsal fin, located midway along the back, can be used to distinguish individual whales because the shape varies from falcate (sickle-shaped) to curved and pointed to triangular. The head is square, with a conical, pointed snout and a small, under-slung jaw. The head measures about 1/6 of the body's length, which is the shortest proportion of any cetacean. The blowhole is located on the left side of the melon, contributing to the marked asymmetry of the skull. A lightly colored crescent-shaped mark may be present on either side of the head between the eye and flipper. This mark is called a false gill due to its resemblance to the gill slits of a fish. The lower jaw of dwarf sperm whales holds 7 to 13 pairs of sharp, curved, homodont teeth, while the upper jaw bears 3 pairs of vestigial teeth which are sharp, thin, and lack enamel. The throat region is grooved with several short longitudinal creases. (Culik, 2010; Petrie, 2005; Reeves and Leatherwood, 1983)

The mating system of dwarf sperm whales is not known.

Little information is known about reproduction in this species. The mating process is likely to be similar to other cetaceans: as both females and males align themselves belly to belly, the male inserts his penis into the female's genital canal, and fertilization occurs internally. The gestation period is 9 months and the duration of the calving season appears to last at least 5 or 6 months. There appears to be at least one calving peak during summer months. Frequent observations of pregnant females accompanied by unweaned calves suggest an annual reproductive cycle with one calve per year. (Culik, 2010; Eder, 2001; Petrie, 2005; Reeves and Leatherwood, 1983)

Specific information on parental care of young is lacking for dwarf sperm whales. It may be that they cares for their young in ways similar to more well-studied cetaceans, wherein females and their calves stay together in pods for months to years. Females nurse and protect their young, but it is not known if dwarf sperm whales employ extramaternal care by related females within the pod or by males. Their ability to excrete fecal matter to distract predators can be considered an additional means of protecting their offspring. (Culik, 2010; Petrie, 2005)

The lifespan and longevity of this species is unknown in the wild, and only a few specimens have survived more than a year in captivity. Based on necropsies of stranded individuals, ingested plastic debris found within the stomach is a clear cause of morbidity and mortality. Furthermore, entanglement and drowning in gills nets is also a serious problem contributing to premature mortality. (Reeves, 2006)

Dwarf sperm whales are timid, rarely approaching boats. They have been seen in small groups of 6 to 10 or alone and slowly swimming or floating at the surface. When beginning to dive, they often just sink down without having their flukes break the surface. (Eder, 2001; Scott and Cordaro, 1987)

The long and short-range movements of dwarf sperm whales are unstudied, so information on home range is lacking. However, some groups appear to exhibit site fidelity around the Hawaiian Islands. (Reeves and Leatherwood, 1983)

Information on communication and perception of dwarf sperm whales cannot be found. However, as members of the family Physeteridae, it seems reasonable to assume that they use echolocation (sonar) and vocal communication in similar ways to their cousins, sperm whales. (Madsen, et al., 2002a; Madsen, et al., 2002b; Stoops, et al., 1996)

The diet of dwarf sperm whales consists mainly of cephalopods, especially the squid species Ancistrocheirus lesueurii, Histioteuthis species, Chiroteuthis veranyi, and Octopoteuthis species, though fish and crustaceans also form part of the diet. Echolocation is probably used to locate prey since these whales forage in dimly lit zones of the ocean. (Stoops, et al., 1996; dos Santos and Haimovici, 2009)

Dwarf sperm whales appear to employ a suction feeding strategy to capture prey. (Bloodworth and Marshall, 2005)

While there are no direct observations of predation on K. sima, its small size would make it potential prey for larger carnivores such as killer whales (Orcinus orca) and great white sharks (Carcharodon carcharias). When threatened, dwarf sperm whales eject a concealing fluid as a decoy, much like a squid does. They excrete a dark reddish-brown liquid from a sac located in the lower portion of the intestine. It can eject over 12 liters of liquid to create a dense cloud which may frighten predators or distract them, allowing the whale to swim away. Their coloration also helps to camouflage them in ocean waters. (Culik, 2010; Folkens and Reeves, 2002)

As predators, dwarf sperm whales play an important role in the ocean ecosystem linking the midwater zone to the epipelagic zone. Spearfish remoras (Remora brachyptera) share a commensal relationship with K. sima individuals by attaching themselves to the whales with their modified dorsal fins. Furthermore, dwarf sperm whales host many types of endoparasites in their intestines. ("Report on Marine Mammal Unusual Mortality Event UMESE0501Sp: Multispecies Mass Stranding of Pilot Whales (Globicephala macrorhynchus), Minke Whale (Balaenoptera acutorostrata), and Dwarf Sperm Whales (Kogia sima) in North Carolina on 15-16 January 2005", 2006; Colón-Llavina, et al., 2009)

Dwarf sperm whales are not commercially exploited, though they may be an economically valuable commodity in aboriginal/artisanal fisheries.

There are no known negative impacts on humans. Interactions with humans are rare due to their timid behavior and their tendency to avoid approaching ships and boats. (Culik, 2010)

Population size in the waters around Hawaii has been estimated at about 19,000 individuals, but worldwide estimates are lacking. (Mullin and Fulling, 2004)