Pygmy Killer Whale

About the Species

Despite its common name, the pygmy killer whale is a small member of the oceanic dolphin family. They are often confused with false killer whales and melon-headed whales. This species is found primarily in deep waters throughout tropical and subtropical areas of the world. Until a live animal was discovered in 1954, pygmy killer whales were known only from two fossil skulls for over a century. Not much is known about them, and they are considered naturally rare. 

Although they face threats from entanglement in fishing gear, pygmy killer whales in the United States are not endangered or threatened. Like all marine mammals, they are protected under the Marine Mammal Protection Act. 

Status

NOAA Fisheries estimates population size for each stock of pygmy killer whale in its stock assessment reports. A stock is a group of animals that occupy the same area and interbreed. There are three recognized stocks in the United States: Hawaii, northern Gulf of Mexico, and western North Atlantic. 

Appearance

Pygmy killer whales can reach a length of 8.5 feet and weigh up to 496 pounds. They are about 2.6 feet long as newborns and reach adulthood at 6.5 feet. They have a small head with a rounded melon (or forehead) that extends in front of the mouth, and they have no discernable beak. Their dorsal fin is relatively large and tall and is located behind the mid-back. They have relatively long, pointed, tapering flippers (pectoral fins), and their body is dark gray to black with some small white areas on the lips and belly. They have a fairly prominent, narrow cape that dips only slightly below the dorsal fin and a light gray ventral band.

Pygmy killer whales are easily confused with melon-headed whales because of their similar appearance. The best ways to distinguish between the two species are the pygmy killer whale’s frequent paired white tooth rakes, and the clear demarcation between the pygmy killer whale’s darker cape and lighter lateral pigmentation. 

Behavior and Diet

Pygmy killer whales usually occur in groups of 12 to 50 individuals but have been seen in groups up to several hundred individuals. Both sexes may remain in their birth groups throughout their lives. They are generally less active than other oceanic dolphins and are frequently seen "logging"—resting in groups at the surface with all animals oriented the same way. 

Pygmy killer whales are very aggressive when kept in captivity. They feed primarily on squids and fishes.  

Where They Live

Pygmy killer whales prefer deeper areas of warmer tropical and subtropical waters where their prey is concentrated. They have a circumglobal range from 40 degrees North to 35 degrees South. They may occasionally occur relatively close to shore around oceanic islands. In the United States, they can be found in Hawaii, the northern Gulf of Mexico, and the western North Atlantic. In Hawaii, there are resident populations off Oahu, Penguin Bank, and Hawaii Island. 

Lifespan & Reproduction

Reproductive biology is poorly known in this species. Its estimated lifespan is unknown.  

Threats

Entanglement in Fishing Gear 

Pygmy killer whales can become entangled or captured in commercial fishing gear, such as gillnets, though there is no reported bycatch from U.S. fisheries.  

Ocean Noise

Underwater noise pollution can interrupt the normal behavior of pygmy killer whales, which rely on sound to communicate. As ocean noise increases from human sources, communication space decreases—the whales cannot hear each other, or discern other signals in their environment as they do in an undisturbed ocean. 

Sound can disturb important activities, such as feeding, migrating, and socializing. Scientific research has documented that ocean noise also causes marine mammals to change the frequency or amplitude of their calls, decrease foraging behavior, become displaced from preferred habitat, or increase the level of stress hormones in their bodies.  If loud enough, noise can cause permanent or temporary hearing loss. 

Scientific Classification

Kingdom	Animalia
Phylum	Chordata
Class	Mammalia
Order	Cetacea
Family	Delphinidae
Genus	Feresa
Species	attenuata