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Killer whales description and social organization.
Killer whales Description
- Weight: males can weigh up to 22,000 pounds (10,000 kg); females can weigh up to 16,500 pounds (7,500 kg)
- Length: males can reach 32 feet (10 m); females can reach 28 feet (8.5 m)
- Appearance: black on top with white undersides and white patches near their eyes; highly variable gray or white saddle behind the dorsal fin; these markings are unique across individuals and populations
- Lifespan: up to 50-100 years: males typically live for about 30 years, but can live as long as 50-60 years; females typically live about 50 years, but can live as long as 100 years
- Diet: varies (diet is often geographic or population specific), can include fish, marine mammals, sharks, and sea birds
- Behavior: highly social animals, living within matriarchal societies; rely on underwater sound for orientation, feeding, and communication; produce whistles and pulsed calls, used for communication and maintaining group cohesion
Killer Whale Ecotypes and Forms poster
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.
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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.
Source: http://www.nmfs.noaa.gov/pr/
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