Killer whales most widely distributed marine mammals, found in all parts of the oceans; most abundant in colder waters, including Antarctica, the North Atlantic and Pacific Oceans. They also occur, though at lower densities, in tropical, subtropical, and offshore waters.

Killer whales are generally considered monotypic (belonging to one species). However, genetic studies and morphological evidence have led many cetacean biologists to now consider the existence of multiple species or subspecies of killer whales worldwide.1

The species shows considerable size "dimorphism". Adult males develop larger pectoral flippers, dorsal fins, tail flukes, and girths than females.

Female killer whales reach sexual maturity when they grow to about 15-18 feet (4.6 m-5.4 m) long, depending on geographic region. The gestation period for killer whales varies from 15-18 months. Birth may take place in any month--there is no distinct calving season. Calves are nursed for at least 1 year, and may be weaned between 1-2 years old. The birth rate for killer whales is not well understood, but, in some populations, is estimated as every 5 years for an average period of 25 years.

Killer whales are highly social animals that occur primarily in relatively stable social groups that often range in size from 2 to 15 animals. Larger groups (rarely as large as several hundred individuals) occasionally form, but are usually considered temporary groupings of smaller social units that probably congregate for seasonal concentrations of prey, social interaction, or mating.

Single whales, usually adult males, also occur in Bigg's killer whale populations (as discussed below). Differences in spatial distribution, abundance, behavior, and availability of food resources probably account for much of the variation in group size among killer whale populations.

Populations and Social Organization

Scientific studies have revealed many different populations--or even potentially different species or subspecies--of killer whales worldwide. These different populations of killer whales may exhibit different dietary needs, behavior patterns, social structures, and habitat preferences. Therefore, interbreeding is not expected to occur between different populations, in spite of the overlap between home ranges.

The most well-studied killer whale populations occur in the eastern North Pacific Ocean. Three distinct forms, or ecotypes, of killer whales are recognized:2

Resident
Transient, or Bigg's
Offshore

The three types differ in morphology, ecology, behavior, and genetics. A recent genetic study3 suggests the transient type has been separated from all other killer whales for approximately 750,000 years and might represent a separate species or subspecies, known among researchers as Bigg's killer whales. All three types of killer whales share at least part of a home range, yet they are not known to intermix with one another. The resident and transient types both have multiple populations within their range.

Resident Killer Whales are noticeably different from both transient and offshore forms. The dorsal fin is rounded at the tip and curved and tapering, or "falcate". Resident whales have a variety of saddle patch pigmentations with five different patterns recognized. They've been sighted from California to Russia. Resident whales primarily eat fish.

Resident killer whales in the U.S. North Pacific consist of the following populations:

Southern residents
Northern residents
Southern Alaska residents
Western Alaska North Pacific residents
Resident type killer whales occur in large social groups called "pods," groups of whales that are seen in association with one another over 50% of the time. The pods represent collections of matrilines, their fundamental social unit.

Southern Resident killer whales are the only known resident population to occur in the U.S. Southern residents are comprised of three pods: J, K, and L pods. The Southern Residentsare considered one "stock" under the Marine Mammal Protection Act (MMPA) and one "distinct population segment" (therefore, "species") under the Endangered Species Act (ESA).

The Southern Resident Killer Whale population is currently estimated at about 80 whales, a decline from its estimated historical level of about 200 during the late 1800s. Beginning in the late 1960s, the live-capture fishery for oceanarium display removed an estimated 47 whales and caused an immediate decline in Southern Resident numbers.4 The population fell an estimated 30% to about 67 whales by 1971.5 By 2003, the population increased to 83 whales.6 Due to its small population size, NMFS listed this segment of the population as endangered under the Endangered Species Act (ESA) in 2005 and designated critical habitat in 2006.

Their range during the spring, summer, and fall includes the inland waterways of Washington state and the transboundary waters between the United States and Canada. Relatively little is known about the winter movements and range of the Southern Resident stock. However, in recent years, they have been regularly spotted as far south as central California during the winter months.

More information on Southern Residents can be found on our West Coast Region's website.

Bigg's (Transient) Killer Whales occur throughout the eastern North Pacific, and have primarily been studied in coastal waters. Their geographic range overlaps that of the resident and offshore killer whales. The dorsal fin of transient whales tends to be straighter at the tip than those of resident and offshore whales.7 Saddle patch pigmentation of transient killer whales is restricted to two patterns, and the large areas of black color don't mix into the white of the saddle patch that is seen in resident and offshore types. Transient type whales are often found in long-term stable social units of less than 10 whales, smaller than resident social groups. Transient killer whales feed nearly exclusively on other marine mammals.8

AT1 Transients were one of the most frequently encountered groups and, in the 1980s, were sighted year-round in Prince William Sound. The AT1 group was made up of at least 22 whales, but has been reduced by more than half since the 1989 Exxon Valdez oil spill. Several confirmed deaths of AT1 killer whales have been recorded since the 1990s, while other missing animals are presumed dead.9 In June 2004, NMFS designated the AT1 group of transient killer whales as a depleted stock under the MMPA. Scientists estimate there are only 7 killer whales remaining in this group.

Offshore Killer Whales are similar to resident whales, but can be distinguished generally8 by features such as their:

rounded fins with multiple nicks on the edge
smaller overall size
tendency for males and females to be more similar in size (less "sexual dimorphism")
Offshores have the largest geographic range of any killer whale community in the northeastern Pacific and often occur 9 miles (15 km) or more offshore. But, they also visit coastal waters and occasionally enter protected inshore waters. Animals typically congregate in groups of 20-75 animals with occasional sightings of larger groups up to 200 whales. They are presumed to feed primarily on fish, though they have been documented feeding on sharks. Genetic analyses indicate that offshore killer whales are reproductively isolated from other forms of killer whales. Offshore killer whales are among the least observed and understood of all killer whale populations.

Diet

The diet of killer whales is often geographic or population specific:

Resident killer whale populations in the eastern North Pacific mainly feed on:

salmonids, showing a strong preference for Chinook salmon10
Bigg's (Transient) killer whale populations in the eastern North Pacific feed on marine mammals, such as (in order of frequency of observation):

harbor seals
Dall's porpoises
harbor porpoise
California sea lions
gray whale calves
Steller sea lions
elephant seals
minke whales
various other species of pinnipeds and cetaceans
Off the coast of Norway, some killer whales feed mainly, often in a coordinated manner, on:

herring
other schooling fish
In waters off New Zealand, some killer whales feed on:

stingrays
sharks
In Antarctic waters, there are different types of killer whales. They have each been observed feeding off of various species:

type 'A' killer whales feed on minke whales
type 'B' killer whales feed on seals within the seasonal ice pack
type 'C' killer whales feed on Antarctic toothfish and other fish species

Like all cetaceans, killer whales depend heavily on underwater sound for orientation, feeding, and communication. Killer whales produce three categories of sounds:

clicks
whistles
pulsed calls
Echolocation clicks are believed to be used primarily for navigation and discriminating prey and other objects in the surrounding environment, but are also commonly heard during social interactions and may have a communicative function.

Whistles and pulsed calls are believed to be used for communication and during social activities. Whistles are frequency modulated sounds (pitch changes with time) with multiple harmonics. Pulsed calls are the most common type of vocalization in killer whales and resemble squeaks, screams, and squawks to the human ear. Most calls are highly distinctive in structure, and are characterized by rapid changes in tone and pulse repetition rate.

Killer whales of different populations have distinct calls and whistles. 3In resident killer whales of the eastern North Pacific, each pod possesses a unique repertoire of discrete calls – representing community dialects – which are learned and culturally transmitted among individuals. These calls serve as family badges and are used to maintain group cohesion.11 In instances with high levels of noise, killer whales are known to increase the amplitude (i.e., volume) of their calls.12

Habitat
Killer whales are most abundant in colder waters, including Antarctica, Norway, and Alaska. However, killer whales can also be fairly abundant in temperate waters. Killer whales also occur, though at lower densities, in tropical, subtropical, and offshore waters.