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Introduction

False killer whales can be found all over the world in tropic, subtropical, and temperate waters, generally in offshore waters that are more than 3,000 feet deep. With the exception of north-eastern South America and northern east coast of the US, they are pretty much everywhere except the Poles! In the US they can be found in Hawaii, Pacific remote island areas, Alaska, up and down the west coast (as far north as British Columbia in warm years), the Gulf of Mexico, American Samoa, and the warmer Gulf Stream waters off the East Coast.

Despite their name, false killer whales don’t actually look like killer whales. Their name comes from the similarity of their skulls not their appearance, and genetically they are more closely related to Risso’s dolphins and pilot whales. They are dark gray, appearing black with a small lighter area on their underside between their pectoral fins, running from the throat to the belly.

False killer whales are active at the surface. Notice the darker grey coloration and blunt head. Photo: Protected Resouces Division, Southwest Fisheries Science Center, La Jolla, California

Males are larger (up to 20ft vs. 16ft for females) and can weight up to 3,000lbs. The front of an adult male’s head hangs over the lower jaw more than females, and can be flattened in older males. Their pectoral fins are unique with a distinct hump creating an “S” shape on the outer edge. Individuals can be distinguished using scars on their dorsal fins (often from fisheries interactions) and scars on their body from cookie cutter sharks. Interestingly, scars are eventually re-pigmented, unlike their closely related cousins the Risso’s dolphin (they are known for the massive amount of scars all over their body).

Behavior

The oceanic nature of this species makes them hard to study; most of what is known comes from stranded or captive animals and limited observations of groups around oceanic islands (like Hawaii). False killer whales form strong social bonds, usually found in small subgroups if a few individuals associated with larger aggregations (20-100) that can be spread over tens of kilometers. In the endangered insular population of the Hawaiian Islands they have documented definitive social clusters and long-term associations of up to 15 years, and this population has unique vocalizations compared to the other 2 Hawaiian populations that overlap in range. This endangered population also has strong natal social group fidelity for both sexes, meaning they usually stay with the group they were born in, and that up to 64% of mating involved individuals from the same social group, further reinforcing their strong social connections. These strong bonds can also be a detriment however – they often strand in large groups, as they stay together even if in trouble. The largest recorded mass stranding was 835 individuals!

False killer whales are very social, although sometimes they can be aggressive in interspecies interactions! Photo: source unknown.


These social animals don’t just associate with other false killer whales, but also a variety of other cetacean species, most notably bottlenose and rough toothed dolphins. They can be quite active at the surface, often leaping fully out of the water. False killer whales also practice prey sharing, where one individual will catch a fish, and then share it with other members of the group at the surface. This makes sense with their tight social bonds.

Diet

False killer whales feed both day and night and prey includes many types of fish (like tuna, mahi mahi and wahoo) and squid. They have the ability to adjust their hearing when echolocating, which can be very helpful when trying to find food. Their chases can be quite exciting, and they may leap out of the water and even throw the fish high into the air before eating it. They can dive deep for their prey, one tagged animal dove for 12 min and to over 230 meters, but little else is known about their diving behavior. In Hawai’i they are known to depredate deep-set longline fisheries (these interactions can cause the dorsal fin damage mentioned above).

Groups may increase their ability to detect prey (and perhaps follow fisheries) by individuals separating up to 100km over hours and days before rejoining as a group. Satellite tagged pelagic false killer whales have been documented to move up to 75km in 4 hours and 335km in 24 hours, so they can travel far and keep up with vessels. The most interesting note about their dinner habits is that they have even (though rarely) been documented feeding on smaller delphinids being release from tuna purse-seine nets in the Easter tropical Pacific, one case of predation on a humpback whale calf and have been documented attacking sperm whales (though consumption was not observed/confirmed).

Reproduction

False killer whales become sexually mature around 8-14 years of age, though it is thought that males may mature later, with one source saying even 8-10 years later. Their gestation is 11 to 16 months and they will nurse their calves 1.5-2 years. Calving may occur year round, but often peaks in late winter. How often they give birth is not known, but one estimate is every 7 years. Females will enter menopause around 44-55 years of age.

False killer whales can be extremely acrobatic at the surface. Photo: Lee Bertrand.

Current Status

There is currently no global population estimate for false killer whales due to their pelagic habitat – it’s simply too difficult to count them when they’re mostly offshore! Generally, false killer whales are listed as “Near Threatened”, and the Hawaiian Islands insular population specifically is listed as “Endangered”, with less than 200 individuals thought to remain.

Threats

  • Fisheries Interactions: The most common threat to false killer whales is interactions with fisheries. Due to their pelagic distribution, they come into contact with larger fishing vessels and oceanic fishing boats frequently, as well as more coastal fishing efforts in some of the Island areas. They are known to take bait and catch off fishing lines, a risky behavior which can result in the false killer whale getting hooked on the line (known as an accidental take), injured, or even killed or maimed by fishermen trying to cut them off the hooks. Evidence of this behavior is particularly frequent in the Hawaiian Islands insular stock.
  • Prey Depletion: Living in such close contact with fisheries operations also means that false killer whales are in direct competition for prey with the fishermen. Although prey depletion doesn’t currently seem to be a major issue, it’s important to keep an eye on fish stocks and the amount of prey available to these animals.
  • Small Population Sizes: For small populations such as the Hawaiian Insular population, the diversity of genes within the population is very limited (especially since the animals predominantly breed within the same population). This could result in a genetic bottleneck, where the population breeds only within itself without any outbreeding resulting in an increase in deleterious genes, genetic mutation, and/or susceptibility to disease. Conversely, smaller population sizes can also mean intensified competition for food within that region, as all the animals must be able to subsist on the prey in that particular location.
  • Active Hunting: Seen as pests, false killer whales are still actively hunted in several parts of the world including Indonesia, Japan, and the West Indies.
  • Contaminants: Like many of the top predators in the ocean, false killer whales are prone to bioaccumulation of toxins. This is particularly true for this species as they consume large, predatory fish species, which themselves often have higher levels of contamination than smaller bait fish.

Fun Facts

  • The false killer whale’s scientific name, Pseudorca crassidens, means “thick tooth”, a reference to their pointed teeth and fierce, predatory behavior in the open oceans!
  • They can live up to 60+ years, with the oldest female reaching 63 years and the oldest male recorded at 57 years old.
  • They produce a wide range of vocalizations including clicks, buzzes, burst-pulsed calls, whistles, click trains, and more!
  • They can swim up to 18 mph (29 kmph), however their typical speed is thought to be closer to 9-10mph (~15kmph).
  • False killer whales have been able to successfully interbreed with bottlenose dolphins in captivity, resulting in a fertile hybrid offspring known as a “wholphin”! Wholphins have dark grey skin (a perfect mixture of the almost-black of the false killer whale, and the light grey of the bottlenose) and, strikingly, have 66 teeth: this is the exact average of its parents (false killer whales typically have 44 teeth, and bottlenose dolphins have 88!).
Kekaimalu is the first confirmed wholphin, born in captivity in Hawaii. Note the shortened beak and darker grey coloration. Photo: InfyWorld.com

cindy.elliser@pacmam.org

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