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: Resident, Transient (also called Bigg’s) and Offshore.
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.
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 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. The population fell an estimated 30% to about 67 whales by 1971. By 2003, the population increased to 83 whales. Due to its small population size, NOAA listed this segment of the population as endangered under the Endangered Species Act (ESA) in 2005 and designated critical habitat in 2006.
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. 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.