Killer whales are endangered due to a number of threats, including oil spills, bio-accumulation of PCB and other contaminants, noise pollution, collisions with ships, entanglement in fishing gear, shootings by fishermen, and habitat disturbance by whale watchers. Additionally, the depletion of populations of prey, such as marine mammals and certain species of fish, affects its ecosystem.
Past threats to killer whales include capture for use in aquarium exhibits and commercial hunting. Although few killer whales are hunted for their commercial value as of 2014, they continue to be shot by commercial fishermen, who view them as competitors. Since the Exxon Valdez oil spill in 1989, oil spills and other leaks of pollutants have been regarded as serious threats to killer whales. Noise disturbances that affect killer whales include Naval high-intensity sonar, which CAT scans proved causes hemorrhaging around their brains and ears, as well as sound from drilling, shipping and salmon farms.
In 2013, the International Union for Conservation of Nature and Natural Resources Red List of Threatened Species listed the taxonomic unit of killer whales as data deficient. Previously, killer whales had been regarded as one species, but researchers posit that there may be several species of killer whales, some of which are endangered as of 2014. Resident killer whales move in pods and inhabit specific areas, whereas transient killer whales move in smaller groups and range in larger areas. Southern resident killer whales, for instance, a group of three large pods that inhabit the coastal waters of the western United States and Canada, were declared an endangered species under the Endangered Species Act in 2005, and the National Oceanic and Atmospheric Administration declared their range a critical habitat subject to conservation in 2006.