False Killer Whale

False killer whales are social animals found globally in all tropical and subtropical oceans and generally in deep offshore waters. The false killer whale’s entire body is black or dark gray, although lighter areas may occur ventrally (on its underside) between the flippers or on the sides of the head.

Fishery interactions is one of the main threats facing this species. False killer whales are known to depredate (take fish and bait off of fishing lines), which can lead to hooking and/or entanglement. This is especially a concern for false killer whales that interact with the Hawaiʻi longline fishery.

Due to its very small population size (about 150 individuals) and population decline in recent decades, the main Hawaiian Islands insular false killer whale distinct population segment (DPS) is listed as endangered under the Endangered Species Act. It is the only false killer whale population protected under the ESA. This stock is also listed as depleted under the Marine Mammal Protection Act.

NOAA Fisheries is committed to conserving and protecting false killer whales. Our scientists and partners use a variety of innovative techniques to study and protect this species. The broad pelagic distribution of most false killer whale populations make it difficult to estimate the global population size of this species.

The endangered main Hawaiian Islands insular false killer whale is estimated to number around 150 whales. The historical population size is unknown, though spotter planes in the late 1980s observed large aggregations of 350 to 400 whales in a single area. Aerial survey sightings since then suggest that the main Hawaiian Islands insular false killer whale population declined at an average rate of 9 percent per year through at least the early 2000s. The current population trend is unknown.

The cause of this decline is unknown, but it’s thought to be partially due to interactions with fisheries, especially before 1990 when longline fishing was more common in Hawaiʻi’s nearshore waters. Annual variability in survey efforts within the range of the main Hawaiian Islands insular false killer whale make it difficult to assess population trends, so it’s unknown whether the population has continued to decline, recently stabilized, or recently increased.

A survey conducted in 2010 estimated the Hawaiʻi pelagic population of false killer whales to be roughly 1,550 individuals. Their historical population size is also unknown, though interactions with longline fisheries are known to have killed or seriously injured animals in this population since at least the late 1990s. There have been few large-scale surveys in Hawaiian waters, and changes in survey design (intended to provide more precise estimates given the social structure and behavior of false killer whales) make it difficult to determine trends in abundance for this pelagic population.

The Northwestern Hawaiian Islands, northern Gulf of Mexico, and western North Atlantic stocks (populations) are not as well-studied. Current population abundance estimates for all stocks (Hawaiian, the northern Gulf of Mexico, and the western North Atlantic) can be found in the latest  marine mammal stock assessment reports. False killer whales are large members of the dolphin family. They are dark gray, often appearing black on all but a small part of their ventral (underside) surface, which is lighter between the pectoral fins running from the throat down to the belly.

The species is large and slender, and males are slightly larger than females. They have a small conical head without a beak. The front of an adult male’s head hangs over the lower jaw to a greater extent than in females and is flattened in older males.

The pectoral fins or flippers have a distinct central hump creating an S-shape along the outer edge. The dorsal fin is located in the middle of the back and generally curves backward. In Hawaiian waters, dorsal fin shapes show a lot of variability, often caused by injury from fishery interactions.

Adult females reach lengths of 16 feet, while adult males are almost 20 feet long. In adulthood, large false killer whales can weigh up to 3,000 pounds.

Scientists can photo-identify individual whales through unique natural markings, such as scars to false killer whales’ dorsal fins or scars from cookie cutter sharks. These prominent markings to the body and dorsal fin help distinguish one whale from another. False killer whales are gregarious and form strong social bonds. They are often found in relatively small subgroups of a single to a few individuals that are associated with a larger aggregation that may spread over tens of kilometers. These strong social bonds between groups and dispersion into small subgroups likely help them find prey.

When they capture prey, many individuals tend to converge, and their prey items may be shared among several animals in the group. In Hawaiʻi, these larger aggregations may include 40 to 50 animals altogether, whereas larger groups have been observed in other regions. They are known to strand in groups as well. In some regions, false killer whales are also found with other cetaceans (whales and dolphins), most notably bottlenose dolphins.

Although the range of the main Hawaiian Islands insular false killer whale partially overlaps with the ranges of the Hawaiʻi pelagic and Northwestern Hawaiian Islands populations, genetic analyses, photo-identification, and social network analyses indicate that the main Hawaiian Islands insular false killer whale population consists of a tight social network that is socially unconnected with the other two Hawaiʻi-based populations.

In addition to the social structure found among all three Hawaiian false killer whale populations, there is significant social structure within the main Hawaiian Islands insular population. A social network analysis indicates that this population can be broadly divided into four primary social clusters.

False killer whales are top predators that primarily hunt fish and squid. They feed both during the day and at night, hunt in dispersed subgroups, and converge when prey is captured. Prey sharing has also been observed among individuals in the group.

False killer whales can dive for up to 18 minutes and swim at high speeds to capture prey at depths of 300 to 500 meters. They often leap completely out of the water, particularly when attacking certain prey species. In Hawaiʻi, they are also known to throw fish high into the air before consuming them. False killer whales generally prefer offshore tropical to subtropical waters that are deeper than 3,300 feet.

Both main Hawaiian Islands insular false killer whales and Northwestern Hawaiian Islands false killer whales maintain a more island-associated habitat, preferring to remain close to the Hawaiian Islands. This is likely due to the islands’ unique oceanographic setting, which concentrates and aggregates prey.

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False killer whales occur in tropical, subtropical, and temperate waters of all ocean basins. In the United States, they are found around Hawaiʻi, in all Pacific Remote Island Areas, the Mariana Archipelago, and in American Samoa, as well in the Gulf of Mexico and in the warm Gulf Stream waters off the East Coast. False killer whales have been observed off the U.S. West Coast as far north as British Columbia, Canada, typically during warmer oceanographic regimes. The oldest estimated age of false killer whales (based on growth layers in teeth) is 63 years for females and 58 years for males.

Female false killer whales reach sexual maturity between the ages of 8 and 11, while males mature 8 to 10 years later. Gestation ranges from 11 to 16 months, and lactation occurs for 1.5 to 2 years. Time between births is unknown, but is estimated to be around 7 years. Female false killer whales enter menopause and become less reproductively successful between 44 and 55 years old. Fishery interactions occur when false killer whales take (or depredate) bait and catch off fishing lines. This action can result in incidental take—unintentional hooking and/or entanglement—as well as serious injury and/or death. False killer whales in Hawaiʻi, particularly main Hawaiian Islands insular false killer whales, have a high rate of dorsal fin injuries and mouthline injuries, likely caused by efforts to take bait and catch from fishing lines.

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Prey items for false killer whales are similar to many of the same species that fisheries target. This is particularly true in Hawaiʻi, where preferred fish for both false killer whales and consumers are tuna, billfish, wahoo, and mahimahi. Competition with fisheries can result in smaller and fewer prey for false killer whales, requiring them to spend more time and energy hunting for food.

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False killer whales are long-lived, upper-trophic-level predators (that is, they’re near the top of the food chain), so they accumulate high levels of toxins from the marine environment. Exposure to toxic chemicals in the marine environment, including persistent organic pollutants (industrial chemicals and pesticides, heavy metals, etc.), can result in a number of biological effects to marine mammals, such as diseases and reproductive issues. It can also affect the quality and quantity of false killer whales’ prey. Although the United States has banned many of these chemicals, some continue to be used in other regions of the world and can be transported via atmospheric means or ocean currents.

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The small size of the endangered main Hawaiian Islands insular false killer whale population poses a unique threat to this group. Within a small, highly social population, the potential for reduced genetic diversity increases, potentially making the population more vulnerable to diseases or other environmental changes. Such environmental events may further harm the population by causing a genetic bottleneck—a reduction in the variation of the gene pool that only rebounds when the population breeds with other populations or enough random genetic mutations have accumulated over many generations. Such a small population may also suffer from a breakdown of cooperative feeding if an aggregation is not large enough to find adequate food.

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False killer whales are hunted in other parts of the world, including Indonesia, Japan, and the West Indies.