Orca ( Killer Whale )
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The killer whale, also known as orca, is the ocean’s top predator. It is the largest member of the Delphinidae family, or dolphins. Members of this family include all dolphin species, as well as other larger species, such as long-finned pilot whales and short-finned pilot whales, whose common names also contain "whale" instead of "dolphin."
Scientific Classification
| Kingdom | Animalia |
|---|---|
| Phylum | Chordata |
| Class | Mammalia |
| Order | Cetacea |
| Family | Delphinidae |
| Genus | Orcinus |
| Species | orca |
Found in every ocean in the world, they are the most widely distributed of all cetaceans (whales and dolphins). Scientific studies have revealed many different populations with several distinct ecotypes (or forms) of killer whales worldwide—some of which may be different species or subspecies. They are one of the most recognizable marine mammals, with their distinctive black and white bodies. Globally, killer whales occur in a wide range of habitats, in both open seas and coastal waters. Taken as a whole, the species has the most varied diet of all cetaceans, but different populations are usually specialized in their foraging behavior and diet. They often use a coordinated hunting strategy, working as a team like a pack of wolves.
Hunters and fishermen once targeted killer whales. As a result, historical threats to killer whales included commercial hunting and culling to protect fisheries from killer whales. In addition, although live capture of killer whales for aquarium display and marine parks no longer occurs in the United States, it continues to remain a threat globally. Today, some killer whale populations face many other threats, including food limitations, chemical contaminants, and disturbances from vessel traffic and sound. Efforts to establish critical habitat, set protective regulations, and restore prey stocks are essential to conservation, especially for the endangered Southern Resident killer whale population.
Appearance
Killer whales are mostly black on top with white undersides and white patches near the eyes. They also have a gray or white saddle patch behind the dorsal fin. These markings vary widely between individuals and populations. Adult males develop disproportionately larger pectoral flippers, dorsal fins, tail flukes, and girths than females.
Behavior and Diet
Killer whales are highly social, and most live in social groups called pods (groups of maternally related individuals seen together more than half the time). Individual whales tend to stay in their natal pods. Pods typically consist of a few to 20 or more animals, and larger groups sometimes form for temporary social interactions, mating, or seasonal concentrations of prey.
Killer whales rely on underwater sound to feed, communicate, and navigate. Pod members communicate with each other through clicks, whistles, and pulsed calls. Each pod in the eastern North Pacific possesses a unique set of calls that are learned and culturally transmitted among individuals. These calls maintain group cohesion and serve as family badges.
Although the diet of killer whales depends to some extent on what is available where they live, it is primarily determined by the culture (i.e., learned hunting tactics) of each ecotype. For example, one ecotype of killer whales in the U.S. Pacific Northwest (called Residents) exclusively eats fish, mainly salmon, and another ecotype in the same area (Transients or Bigg’s killer whales) primarily eats marine mammals and squid.
Killer whales often use a coordinated hunting strategy and work as a team to catch prey. They are considered an apex predator, eating at the top of the food web.
Where They Live
Killer whales are found in all oceans. While they are most abundant in colder waters like Antarctica, Norway, and Alaska, they are also found in tropical and subtropical waters. The most well-studied killer whale populations occur in the eastern North Pacific Ocean. Resident killer whales have been seen from California to Russia. Offshore killer whales have the largest range of any community, and often occur more than 9 miles offshore. They are not, however, exclusively “offshore”, as they are sometimes seen in coastal nearshore waters. Transient killer whales also occur throughout the eastern North Pacific, and are often seen in coastal waters. Their habitat sometimes overlaps with Resident and Offshore killer whales.
Lifespan & Reproduction
The average lifespan for male killer whales is about 30 years, but they can live up to at least 60 years. Females typically live about 50 years, but can live up to at least 90 years in the wild.
Females reach sexual maturity when they are between 10 and 13 years old. They are typically pregnant for 15 to 18 months and give birth to a single calf. Calves nurse exclusively for at least a year, but remain in close association with their mother for the first two years. There is no distinct calving season, so birth can take place in any month. The birth rate for killer whales is not well understood. In some populations, birth rate is estimated at every 5 years for an average period of 25 years. Killer whales, beluga whales, narwhals, short-finned pilot whales, and humans are the only known species that go through menopause.
Threats
Entanglement
Killer whales are at high risk of becoming entangled in fishing gear. Once entangled, whales may drag and swim with attached gear for long distances or be anchored in place and unable to swim. Events such as these result in fatigue, compromised feeding ability, or severe injury, which may ultimately lead to death.
Lack of Food
Overfishing and habitat loss have decreased the amount of prey available to some killer whales. Without enough prey, killer whales might experience decreased reproductive rates and increased mortality rates. This threat is especially important for Southern Resident killer whales because some populations of their preferred prey, Chinook salmon, are also threatened or endangered.
Contaminants
Contaminants enter ocean waters and sediments from many sources, such as wastewater treatment plants, sewer outfalls, and pesticide application. Once in the environment, these substances move up the food web and accumulate in top predators, such as killer whales because of their long lifespan, position at the top of the food chain, and blubber stores. These contaminants can harm killer whales’ immune and reproductive systems.
Despite modern pollution controls, chemical contamination through the food web continues to threaten killer whales. These controls have reduced, but not eliminated, many contaminants in the environment. Additionally, some of these contaminants persist in the marine environment for decades and continue to threaten marine life.
Oil Spills
The 1989 Exxon Valdez oil spill in Prince William Sound, Alaska, was strongly correlated with the direct loss of individual killer whales. However, oil spills can also have an indirect impact on killer whales by affecting the abundance of prey species. In addition, the bioaccumulation of certain contaminants, like those found in oil, such as polychlorinated biphenyls (PCBs) in the food web can be seen in apex predators like killer whales—and particularly among the transient population.
Disturbance from Vessels and Sound
When vessels are present, killer whales hunt less and travel more. Noise interference from vessels, as well as from industrial and military activities, interrupts killer whales’ ability to use sound, which in turn disturbs their feeding, communication, and orientation. Increased vessel noise causes Southern Resident killer whales to call louder, expending more energy in the process.
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