Pygmy killer whales are aggressive and don't have many natural predators. Some potential predators include orcas, large sharks, and humans (Encyclopedia of Life, 2003).
Known Predators:
Pygmy killer whales were first documented in 1827 by J. Gray, using a skull. Gray gave them an alternate name. Pygmy killer whales were subsequently documented again in 1874 by Gray, at which time he called them Feresa attenuata. From 1960 to the present the name Feresa attenuata has been the recognized name (Zerbini and de Oliveira Santos, 1997).
On average, pygmy killer whales weigh 150 kg and are 2.3 meters in length (Madsen, Kerr, and Payne, 2004; Williams et al., 2002; MarineBio, 1998; IUCN Red List of Threatened Species, 2009). Pygmy killer whales are easily misidentified as either juvenile false killer whales or melon-headed whales (McSweeney et al, 2008). Some of the distinguishable features of Feresa attenuata include: a dark gray-black stout body, significantly lighter underbelly, blunt head without a beak, and an under slung jaw which usually contains a whitish color set of lips. The dorsal fin is nearly centered on the body and the flippers have rounded tips and are of moderate length. The dorsal fin itself is one of the best ways to distinguish this mammal from other cetaceans; it reaches high off the dorsal back, lacks rigidity, points slightly backward, and has a sub-triangular shape. Another physical characteristic is an extending groove on the pygmy killer whale's skin, from just ahead of the umbilicus to the anus. This feature holds the genitals, anus, and umbilicus in both sexes (Encyclopedia of Life, 2003); however the presence of a ventral, post-anal keel could be a definite distinction between males and females (McSweeney et al, 2008).
The bone structure of pygmy killer whales is fairly distinctive; not only is the mandible hollow, but the left side is larger and usually contains one more tooth than the right. This difference in size makes the skull asymmetrical, common in many odotocete whales. The lower jaw holds between 11 and 13 large, conical pairs of teeth while the upper usually holds 8 to 11. Off the Brazilian coast, scientists recorded measurements of a stranded female, noting that physical maturity in this species is most likely reached when the vertebral epiphyses and centra in all vertebrae are fused. Also useful in distinguishing mature pygmy killer whales from juveniles is that each tooth's pulp cavity is filled and that ossified cranial sutures occur in adults (Zerbini and de Oliveira Santos, 1997). The distance between the end of the tooth row and the ante-orbital notch is another distinctive characteristic used in identifying a pygmy killer whale that was stranded in the Delta of Parnaíba River, Brazil (De Magalhaes et al, 2007).
Range mass: 110 to 170 kg.
Average mass: 150 kg.
Range length: 2.1 to 2.6 m.
Average length: 2.3 m.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
Little is known about longevity of pygmy killer whales. In a study in the Hawaiian Islands that lasted over 21 years, scientists identified at least one individual pygmy killer whale throughout the entire study (McSweeney et al, 2008).
Range lifespan
Status: wild: 21 (high) years.
Pygmy killer whales depend on their hearing for communication, hunting, and interacting with the marine world around them (Montie, 2011). Rarely kept captive, they have only been studied during the few chance observations in the wild (IUCN Red List of Threatened Species, 2009). While normally occupying warm, deep waters, pygmy killer whales have been spotted near shallower oceanic islands as well (Ward, Moscrop, and Carlson, 2001). A 21 year study in the Hawaiian Islands focused on whales at depths up to 500 meters; little is known about pygmy killer whales at depths greater than 500 meters, although they have been recorded at depths greater than 2500 meters (McSweeney et al, 2008).
Range depth: 113 to 2,862 m.
Average depth: 1,218 m.
Habitat Regions: temperate ; tropical ; saltwater or marine
Aquatic Biomes: pelagic ; coastal
Pygmy killer whales make clicking and whistling sounds similar to bottlenose dolphins and can growl through their blowholes (Encyclopedia of Life, 2003). Like other dolphins, they use echolocation to navigate their environment. A study done in the Indian Ocean recorded a peak range between 45 and 117 kHz (kilohertz) made through these bimodal clicks; the clicks themselves were short, directional broadband signals with intensity levels ranging from 197 to 223 dB (decibels). Both frequency and intensity were higher than false killer whales.
Anatomical studies done on 2 stranded pygmy killer whales off a Florida beach in 2008 provided insight into sound perception. Acoustic vibrations travel through blubber in hollow jawbones. This blubber presses against the tympanoperiotic complex, transmitting the sound to the middle and inner ear. There are two regions of the brain, the medial geniculate body and inferior colliculus, as well as the auditory nerve, that recieve and interpret acoustic signals (Montie, 2011). Scientists were able to document that pygmy killer whales perceived frequencies at 40 kHz best. The lowest audible threshold was about 20 kHz whereas the highest was 120 kHz (Montie, 2011).
Communication Channels: tactile ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Some of the potential threats to this species include fishing and harvesting (intentionally killing for subsistence by humans or accidental mortality from bycatches), pollution, such as solid waste and garbage, noise pollution from sonar, and climate change that can alter habitat (IUCN Red List of Threatened Species, 2009). Although it is not known for certain, the thyroid system of the pygmy killer whale (much like other marine species) could be negatively affected by some man-made pollutants (Montie, 2011). Studies show that estimated population size of pygmy killer whales is 817 in Hawaiian waters, 408 in the northern Gulf of Mexico, and 38,900 in the tropical Pacific (IUCN Red List of Threatened Species, 2009).
US Federal List: no special status
CITES: appendix ii
State of Michigan List: no special status
IUCN Red List of Threatened Species: data deficient
Pgymy killer whales have no negative impact on humans.
There are no known positive impacts of pygmy killer whales on humans.
Pygmy killer whales prey on fish, mollusks, and small cetaceans. Little research has been done to determine the potential parasites or diseases of Feresa attenuata, although they are known to harbor nematode parasites, Anisakis simplex (Zerbini and de Oliveira Santos , 1997)
Commensal/Parasitic Species:
Little is known about the diet of this species. However, based on stomach contents of several stranded specimens, pygmy killer whales have been known to consume cephalopods (Williams et al., 2002), large fish, octopus, squid, (MarineBio, 1998), and smaller cetaceans (Madsen et al., 2004). Scientists believe that these whales feed in deep waters at night (McSweeney et al, 2008).
Animal Foods: mammals; fish; mollusks; aquatic crustaceans; other marine invertebrates
Primary Diet: carnivore (Piscivore , Molluscivore )
Pygmy killer whales account for less than 1% of odontocete sightings (McSweeney et al, 2008). Although pygmy killer whales are rarely seen in the wild, they have been recorded as far north as the Bay of Biscay near France (Williams et al., 2002) and as far south as the African cape (Perrin, 2010). They have been found at numerous locations worldwide, between 45˚ north and 35˚ south latitude; unfortunately, this species has not been reliably found in any one area (McSweeney et al., 2008). They are typically found in deep (Ward, Moscrop, and Carlson, 2001), warm temperate, sub-tropical and tropical waters all over the globe (Williams et al., 2002). They have been recorded most frequently in the temperate waters of the Pacific and south Atlantic Oceans, near the Hawaiian Islands (McSweeney et al, 2008), in the Gulf of Mexico, near Japan, in the Indian Ocean and in tropical western Africa (MarineBio, 1998).
The following locations have been documented for pygmy killer whale sightings: the Venezuelan Caribbean, Puerto Rico, British Virgin Islands, Trellis Bay (Ward, Moscrop, and Carlson, 2001), Florida (Montie, Manire, and Mann, 2011), Brazil, Argentina, South Africa (Zerbini and de Oliveira Santos, 1997), Central English Channel, Bay of Biscay (Williams, Williams, Brereton, 2002), Maldivian archipelago, south of Sri Lanka (Madsen, Kerr, and Payne, 2004), West Indian area, South Atlantic, Pacific Ocean, Indian Ocean, Peru, Gulf of Mexico, western Africa (MarineBio, 1998), and the Hawaiian Islands (McSweeney et al, 2008).
Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native )
Other Geographic Terms: cosmopolitan
Pygmy killer whale mating behaviors are not reported in the literature.
Although there is very little data on the mating system of the pygmy killer whale, scientists believe that at lengths greater than 2.16 meters, males become sexually mature, and at lengths greater than 2.21 meters females become sexually mature (MarineBio, 1998).
Unfortunately gestation period, mating habits, or parental care, are unknown for this species. Other delphinids of similar size birth in the summer months, usually producing one calf (MarineBio, 1998). Pygmy killer whale calves measure roughly 0.8 meters (32 inches) at birth (Ward et al., 2001). One calf is born with each pregnancy.
Average number of offspring: 1.
Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Although it is fairly easy to distinguish nursing, female Feresa attenuata from males and juveniles, there are no studies about parental investment in this species. Generally, in a pod of newly born calves, adults nearest to the calves are the mothers, while other adults without calves are most often males. Besides viewing the adult females near the calves, there is little research about how long the mothers care for their young, or if the males help at all. Like most whales, young pygmy killer whales are born able to swim on their own (McSweeney et al, 2008).
Parental Investment: precocial ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)
The pygmy killer whale (Feresa attenuata) is a poorly known and rarely seen oceanic dolphin.[3] It is the only species in the genus Feresa. It derives its common name from sharing some physical characteristics with the orca also known as the killer whale. It is the smallest cetacean species that has the word "whale" in its common name.[4] Although the species has been known to be extremely aggressive in captivity, this aggressive behavior has not been observed in the wild.[5]
The species had been described by John Gray in 1874, based on two skulls identified in 1827 and 1874. The next recorded sighting was in 1952 which led to its formal naming by Japanese cetologist Munesato Yamada in 1954.[6]
The pygmy killer whale is dark gray to black on the cape and has a sharp change to lighter gray on the sides. The flesh around their lips and on the end of their snout is white while pinkish white skin surrounds the genitals. The average length is just over two meters (6.5 ft.). Upon reaching 2 meters in length, males are considered sexually mature. They have approximately 48 teeth, with 22 teeth on the top jaw and 26 on the lower jaw.[7]
They travel approximately 3 km/hour (2 miles/hour)[8] and are predominately found in deeper waters ranging from 500 m to 2000 m (1600–6500 ft.) in depth.[3]
Pygmy killer whales are most commonly confused with melon-headed whales and false killer whales. For instance, a published paper describing an encounter with a school of pygmy killer whales[5] was later determined to be either a mixture of pygmy and false killer whales or solely false killer whales.[9]
The three species can be differentiated by physical differences between them. One defining difference is, although both species have white around the mouth, on pygmy killer whales the white extends back onto the face. Pygmy killer whales also have rounded-tipped dorsal fins, as opposed to pointed tips. When compared to false killer whales, pygmy killer whales have a larger dorsal fin. Finally, pygmy killer whales have a more clearly defined line where the dark dorsal color changes to the lighter lateral color than either of the other two species.[9]
Behavioral differences can also be used to differentiate pygmy killer whales from false killer whales. Pygmy killer whales usually move slowly when at the surface whereas false killer whales are highly energetic. Pygmy killer whales rarely bow ride but it is common in false killer whales.[9]
The small size of this species also causes confusion with other dolphins especially where the frontal head shape of the animals encountered remains unseen. Unlike the melon-headed whale, pygmy killer whales do not normally lift the full face above the water as they surface to breathe so it is not easy to confirm the lack of a bottle. Furthermore, in calmer waters the small bow wave pushed in front of the face looks like a bottle from a distance.[10]
Prior to the 1950s, the only record of pygmy killer whales was from two skulls identified in 1827 and 1874. In 1952, a specimen was caught and killed in Taiji, Japan which is known for its annual dolphin hunts. Six years later, in 1958, an individual was killed off the coast of Senegal. In 1963, there were two recorded events involving pygmy killer whales. The first was in Japan, where 14 individuals were caught and brought into captivity; all 14 animals were dead within 22 days. The second was off the coast of Hawaii where an individual animal was caught and successfully brought into captivity. In 1967, a single pygmy killer whale off of Costa Rica died after becoming entangled in a purse seine net. Finally, in 1969, a pygmy killer whale was killed off the coast of St. Vincent and a group of individuals was recorded in the Indian Ocean.[6]
Like other oceanic dolphins, pygmy killer whales use echolocation. The centroid of echolocation frequencies is between 70–85 kHz and can range from 32 to 100 kHz. This is similar to the range of other odontocetes such as the bottlenose dolphin but is slightly higher than false killer whales. While echolocating, they produce 8-20 clicks per second with a 197-223 decibel sound level at the production source. The linear directionality of sound production in pygmy killer whales is better than in porpoises but lower than is found in bottlenose dolphins; higher directionality results in sounds that are easier to discern from background noise. Based on similarities to the acoustic parameters of other odontocetes, it is presumed that they use a similar mechanism for producing echolocation clicks.[11]
The anatomy for auditory reception is similar to other odontocetes, with a hollow mandible and a mandibular fat body composed of a low density outer layer and a denser inner core. The inner core comes into direct contact with the tympanoperiotic complex (functionally similar to the auditory bulla in other species - see Cetacea). Hearing tests performed on two live individuals brought in for rehabilitation exhibited frequency response range and temporal resolution similar to that found in other echolocating dolphins. During those tests, one individual exhibited low frequency hearing loss that might have been related to treatment with the antibiotic amikacin although the researchers believed the more likely cause was slight differences in testing setup.[12]
Pygmy killer whales have been observed in groups ranging from 4 to 30 or more individual animals.[3] The only population estimate is of 38,900 individuals in the eastern tropical Pacific Ocean; however, this estimate had a large coefficient of variation meaning the true population size could be much lower or much higher.[13]
The species has a wide distribution in tropical and subtropical waters worldwide. They are sighted regularly off Hawaii and Japan.[14] Appearances in bycatch suggest a year-round presence in the Indian Ocean near Sri Lanka and the Lesser Antilles. The species has also been found in the south-west Indian Ocean in the French Southern and Antarctic Lands off Europa Island, Mozambique[15] and South Africa[16] but not yet recorded off East Africa. In the Atlantic, individuals have been observed as far north as South Carolina on the west and Senegal on the east.[17] They have been observed along the coast of South America and as far north as the Gulf of Mexico where they have been known to breed during the spring season.[5]
A resident population of pygmy killer whales lives in the waters around Hawaii. Most sightings have been around the main island, however there are occasional sightings around several of the other islands. The population has a tightly connected social structure with affiliations between individuals that can last up to 15 years. Despite the existence of this resident population, sightings of pygmy killer whales around Hawaii are still quite rare; they accounted for less than 1.5% of all cetaceans sighted in a study lasting from 1985 to 2007. This population has been observed associating with false killer whales, short-finned pilot whales, and bottlenose dolphins.[3]
Pygmy killer whales have been incidental bycatch in fishing operations. They represent as much as 4% of the cetacean bycatch in drift gill nets used by commercial fisheries in Sri Lanka.[18]
Like other cetaceans, they are hosts to parasitic worms such as cestodes and nematodes. The cestode species, Trigonocotyle sexitesticulae, was first discovered in the corpse of a pygmy killer whale.[19] A pygmy killer whale found stranded on the coast of New Caledonia died from parasitic encephalitis caused by nematodes. They are also victims of opportunistic cookie cutter sharks.[7]
Pygmy killer whales are occasionally involved in mass strandings. As seen in other cetaceans, these strandings often involve a sick or injured individual; even when pushed back out to the sea by rescuers, the healthy individuals will often strand again and refuse to leave until the death of the individual in declining health.[7]
The pygmy killer whale is classified as least concern by the IUCN.[1] They are covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS) and the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS). The species is further included in the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU) and the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU).[20]
The pygmy killer whale (Feresa attenuata) is a poorly known and rarely seen oceanic dolphin. It is the only species in the genus Feresa. It derives its common name from sharing some physical characteristics with the orca also known as the killer whale. It is the smallest cetacean species that has the word "whale" in its common name. Although the species has been known to be extremely aggressive in captivity, this aggressive behavior has not been observed in the wild.
The species had been described by John Gray in 1874, based on two skulls identified in 1827 and 1874. The next recorded sighting was in 1952 which led to its formal naming by Japanese cetologist Munesato Yamada in 1954.
