The false killer whale (Pseudorca crassidens) is a cetacean, and the third largest member of the oceanic dolphin family (Delphinidae). It lives in temperate and tropical waters throughout the world. As its name implies, the false killer whale shares characteristics, such as appearance, with the more widely known Orca (killer whale).
False Killer Whales primarily eat fish and cephalopods, but have been known to attack other small cetaceans in the eastern tropical Pacific during chase and back-down operations of tuna purse seine fishing and, on one occasion, even attacked a humpback whale calf. Depending on location, stomach contents have included salmon (Oncorhynchus sp.), squid (Berryteuthis magister or Gonatopsis borealis) sciaenid and carangid fishes, bonito (Sarda sp.), mahi mahi or dolphin-fish (Goryphaena), yellowfin tuna (Thunnus albacares), yellowtail (Pseudosciana spp.), perch (Lateolabrax japonicus), mackerel, herring and smelt. The most important prey species identified in stomachs of False Killer Whales from the coasts of the Strait of Magellan, Chile were the oceanic and neritic-oceanic squids, Martialia hyadesi and Illex argentinus, followed by the neritic fish, Macruronus magellanicus.
The False Killer Whale was described by Owen in 1846, based on a sub-fossil specimen, and subsequently recognised as a living species. No subspecies are currently recognised, although considerable differences exist between groups from Scotland, South Africa and Australia. Although skull morphology in this species is similar to that of Killer Whales, False Killer Whales are genetically more similar to Risso's Dolphin, Pygmy Killer Whales and the pilot whales.
It is possible that the missing dorsal fin is simply a congenital defect; however the presence of scar material at the site of the missing fin suggests that this is unlikely. Such disfigurements suggest the false killer whales seen around the main Hawaiian Islands are part of the same populations that interacts with long-line fisheries in areas at least 80 km from shores. It is also possible that such disfigurements may have come from interations with other Hawaiian fisheries, such as the nearshore commercial or sports troll fishery, although there is no information available to assess the likelihood of this possibility.
Most false killer whales caught in the long-line ﬁshery are released alive but usually trailing gear and/or with apparent injuries or hooks still embedded. This ﬁshery does not occur within approximately 80 km of the Hawaiian Islands but extends offshore and into international waters outside the Hawai‘i EEZ, as well as into other U.S. territorial waters in the central Paciﬁc. False killer whales in the nearshore waters of the main Hawaiian Islands are genetically distinct from animals in the eastern tropical Paciﬁc Ocean; however, the offshore range of the Hawaiian population has not yet been determined.
A mortality or serious injury of more than a few false killer whales per year is more than the stocks can sustain, because each population consists of no more than a few hundred individuals. The reason these populations are so small is that false killer whales have only one calf every 2-4 years, and as top predators, they do not occur in high densities. Also, like other cetaceans in many parts of the world, false killer whales in Hawaiian waters live in small populations that do not interbreed.
Three “stocks” of false killer whales have been identified in the central Pacific – the Hawaii Insular, Hawaii
Pelagic, and Palmyra Atoll stocks. As defined by the MMPA, the term “stock” means a group of marine mammals of the same species or sub-species in a common spatial arrangement (e.g., animals that share the same habitat), that interbreed when mature. The most recent U.S. Pacific Marine Mammal Stock Assessment Report provides a best estimate of abundance for each stock.
Typical injuries [on false killer whales from getting caught fishing gear] include dorsal fin damage or hooking with trailing gear that leaves the whales unable to swim, gather food or reproduce. Whales can also get tangled in the longliners' miles of lines and drown.
One of the larger members of the dolphin family, false killer whales are rarely seen by humans, as they prefer deep tropical waters. The largest known population lives in the Eastern Pacific.
When the Hawaiʻi-based longline fleet catches yellowfin tuna, mahi mahi, and other target species on its hooks, false killer whales are attracted to this all-you-can-eat buffet and are often wounded or killed by the gear.
The most recent population estimate for the insular population is just 123 individuals. Like the killer whale (not particularly closely related but with a very similar skull), Pseudorca are long-lived (into their 60s), slow to reproduce (having one calf only every 6 or 7 years), and do not start reproducing until their teens. Like humans, females go through menopause, and have a long post-reproductive period.
They share their prey, not only with their companions, but also with humans. A Pseudorca that was alone in British Columbia and Washington from the late 1980s until a few years ago, far from their normal range off Mexico, repeatedly caught large salmon and would offer them to boaters. In Hawaiian waters, Pseudorca have offered fish to human snorklers and divers.