Pseudorca crassidens

30.

False Killer Whale

Pseudorca crassidens

French: Fausse-orque / German: Kleiner Schwertwal / Spanish: Falsa orca

Other common names: False Pilot Whale

Taxonomy. Phocaena crassidens Owen, 1846,

“in the great fen of Lincolnshire beneath the turf [subfossil], in the neighborhood of the ancient town of Stamford,” England, UK.

There are some distinct cranial differences among populations of P. crassidens in waters off Australia, Scotland, and South Africa, and one population off Hawaii appears to be demographically isolated. Nevertheless, genetic variability among populations in the major oceans is low. Monotypic.

Distribution. Worldwide in tropical and warm temperate oceanic waters mainly from ¢.50° N to ¢.50° S, including semi-enclosed seas such as Gulf of California, Gulf of Mexico, Mediterranean Sea, Arabian Sea, Red Sea, Sea ofJapan, and Yellow Sea.

Descriptive notes. Total length 610 cm (males) and 510 cm (females); weight up to 2200 kg (males) and 1200 kg (females). Neonates are 150-200 cm long and weigh ¢.80 kg. The False Killer Whaleis slender in shape with rounded, but not overly bulbous, head and no beak. Flippers have rounded tips and distinct bulge on anterior edge, which gives them a slight “S” shape. Dorsal fin is small and falcate, positioned midway along back. Tailstock is deep, and grooves may be observed in urogenital area. Skin pigmentation is dark gray to black, with a pale-gray patch on chest. Mature male False Killer Whales, in addition to being larger than females, have slightly larger, more protruding melons. Both jaws have 7-12 pairs of large conical teeth.

Habitat. Prefer warm, tropical regions, primarily in deep offshore water. Observations of the False Killer Whale in cooler temperate waters are likely outside its normal distribution. It can be found in the Red and Mediterranean seas. It has been observed in waters with depths of 38-4331 m but is most abundant where depths are more than 3000 m.

Food and Feeding. The False Killer Whale feeds mainly on cephalopods and large fish, including salmon (Oncorhynchus spp.), various oceanic squid (Martialia hyadest, lllex argentinus, Berryteuthis magister and Gonatopsis borealis), bonitos (Sarda sp.), mahi mahi (Coryphaena hippurus), yellowfin tuna (Thunnus albacares), yellowtail (Larimichthys spp.), moonfish (Mene maculata), Indo-Pacific sailfish (Istiophorus platypterus), and Japanese seabass (Lateolabrax japonicus). It is also one of the few cetaceans known to attack and eat other cetaceans, usually small species of delphinids associated with tuna purse-seine fisheries in the eastern Pacific Ocean. They occasionally prey on mysticetes such as the Humpback Whale (Megaptera novaeangliae). Food sharing among individuals has been observed.

Breeding. Mating activity of the False Killer Whale appears to occur throughout the year, but little life history data are currently available and come primarily from studies of stranded individuals. Males and females mature at 8-10 years of age, although males tend to mature slightly later. Birth interval has only been estimated for one population, where it was determined to be almost seven years. Longevity is estimated to be 57 years for males and 62 years for females.

Activity patterns. The False Killer Whale tends to be more active during the day, but there are little data on its diving behavior. Groups travel in line formations that can extend over several kilometersif the group is large. Traveling speeds are 5-20 km/h. False Killer Whales are not shy of boats and are known to bow-ride and otherwise behave energetically or playfully around whale-watching vessels.

Movements, Home range and Social organization. The False Killer Whale is highly social and travels in groups of 20-100 individuals, although larger groups have been reported. Mass strandings have occasionally been in excess of 1000 individuals. Studies of social structure in populations of False Killer Whales off Hawaii indicate that individuals form strong social bonds, and long-term associations lasting up to 15 years are common. As one of the cetacean species known to often mass strand, these strong social bonds come as no surprise. Strong sociality is a factor implicated in mass strandings because a navigational error made by a single individual is likely to be followed by every other individual in the group in a kind of social conformism. The False Killer Whale has also been observed associated with other delphinid species including the Common Bottlenose Dolphin (7 Tursiops truncatus) and the Rough-toothed Dolphin (Steno bredanensis). Little is known about movement and migratory patterns of the False Killer Whale, but a population off Hawaii appears to show strong site fidelity to the archipelago as a whole (although individuals may move substantial distances, up to 283 km, among the islands).

Status and Conservation. CITES Appendix II. Classified as Data Deficient on The IUCN Red List. No overall abundance estimates or population trends for the False Killer Whale are currently available, but it seems to be naturally uncommon,likely making it vulnerable to localized threats. Declines that may result from this vulnerability suggest that a 30% global reduction in abundance over the next three generations is a possibility. Abundance is ¢.16,000 individuals off coastal waters of China and Japan; ¢.298,800 individuals in the eastern tropical Pacific Ocean; ¢.777 individuals in the northern Gulf of Mexico; and ¢.1329 individuals in the Palmyra Atoll. Numbers of resident False Killer Whales around Hawaii are estimated at only 123 individuals. Incidental catch of the False Killer Whale, which occurs throughout its distribution, is probably the most worrisome threat, and monitoring is currently minimal. Incidental catches occur off northern Australia and the Andaman Islands and in Brazilian gillnet fisheries and purse-seine fisheries in the eastern tropical Pacific Ocean. Coastal Chinese fisheries may take several hundred individuals per year in gillnet and trawl fisheries. The False Killer Whale is also vulnerable to long-line fisheries, which are common throughout the central and western tropical Pacific Ocean. Individuals occasionally become hooked when they try to ingest prey items from the lines. Even if an individual escapes, wounds to its gullet from hooks may be lethal. Fishermen sometimes injure or kill False Killer Whales because they take prey items from fishing gear. For example, 900 individuals were killed in 1965-1980 in a culling drive around Iki Island, Japan, to reduce competition with the yellowtail fishery. False Killer Whales are also taken as direct catch off ofJapan and in the Caribbean for meat and cooking oil, and in the past, they were targets of a drive fishery operating off the PenghuIslands of Taiwan. Molecular monitoring of whale meat sold in South Korea has also revealed a high frequency of False Killer Whale meat in local markets. It is taken opportunistically in waters offJapan, Indonesia, Taiwan, and the West Indies. Some individuals caught alive in the Taiwanese and Japanese fisheries have been sold for captive display in aquaria. Other threats to the False Killer Whale, and to most other small cetaceans, include reduced prey availability due to widespread depletion offishery stocks, entanglement in and ingestion of garbage and plastic debris, and vulnerability to loud underwater noise from military activities and seismic exploration—the latter may be particularly damaging given the propensity ofFalse Killer Whales to mass strand.

Bibliography. Alonso et al. (1999), Baird (2009b), Baird, Gorgone et al. (2008), Baker et al. (2006), Chivers et al. (2007), Hernandez-Garcia (2002), Jefferson et al. (2008), Kitchener et al. (1990), Odell & McClune (1999), Taylor et al. (2008f), Wang & Yang Shihchu (2007).