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Overview

Brief Summary

Description

"Pygmy killer whales are among the least-known cetaceans. These black, white-lipped whales have rarely been kept in captivity: from time to time a few stranded animals have been kept for a few days. The scientific history of this species says much about how difficult it is to build up knowledge about cetaceans. A skull from an unknown location was mentioned in the scientific literature in 1827. In 1875, another skull was described and the species was named. In 1952, a ""strange dolphin"" was collected in Japan that proved to be Feresa attenuata. Unfortunately, the scientist who received the specimen got it in pieces, but it provided the first complete skeleton and a hint as to what the animal looked like. Finally, in 1963, several more pygmy killer whales were found in Japan. Thereafter, sightings around the world established that these whales live in temperate and tropical waters, may be aggressive, and prey on small dolphins, fishes, and cephalopods. Information from strandings has provided limited data on size and growth. Pygmy killer whales have been seen swimming alone and in large groups of up to 1,000. Tuna fishermen report seeing groups that average about 25 individuals."

Links:
Mammal Species of the World
  • Original description: Gray, 1875.  J. Mus. Godeffroy.  Hamburg, 8:184.
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Biology

The quick and lively pygmy killer whale is most commonly found in herds of 12 to 50 individuals, although great herds of 100 or more have also been encountered (2). They are known to be playful, having been observed riding the waves around the bow of a boat, leaping high out the water and spyhopping, the act of raising the head and sometimes the upper body vertically out of the water (2). Pygmy killer whales can also be wary of boats and will cluster together when fleeing a disturbance (4). Their feeding habits are not well known but the remains of small fish and cephalopods have been found in the stomachs of stranded pygmy killer whales and, in behaviour that lends a little truth to their name, they are suspected to occasionally chase, attack and even eat dolphins (2).
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Description

Contrary to its name, the little-known pygmy killer whale is actually a member of the dolphin family (2). Until 1952 the pygmy killer whale was only known from two skulls collected in the 19th century, and while more specimens have been collected since it remains one of the least known of the small cetaceans (2). It has a slender, cigar-shaped body that tapers to the tail fin, with a round, blunt head that lacks the beak of many dolphin species (2) (4). The pygmy killer whale is dark grey to black, with lighter sides and a dark 'cape' that extends down the back. Its lips are edged with white and the moderately long flippers are rounded at the tips (2).
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Distribution

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

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Range Description

This is a tropical/subtropical species that inhabits oceanic waters around the globe generally between 40°N and 35°S. It does not generally approach close to shore, except in some areas where deep, clear waters are very close to the coast (such as around oceanic archipelagos like Hawaii). Reports of its occurrence in the Mediterranean Sea, while common in the literature, are not supported by authenticated records. It is also doubtful whether it occurs regularly in the Red Sea or Persian Gulf (Leatherwood et al. 1991). A few high-latitude strandings and sightings are thought to be extralimital records, and are generally associated with incursions of warm water (Ross and Leatherwood 1994; Donohue and Perryman 2002; Williams et al. 2002).
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occurs (regularly, as a native taxon) in multiple nations

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: Apparently widely distributed in tropical and warm subtropical waters; has been encountered off Florida and the West Indies, in the Mediterranean Sea, Indian Ocean, southeastern Atlantic Ocean, and tropical Pacific. Frequently seen in the eastern tropical Pacific, and near Hawaii and Japan (Leatherwood and Reeves 1983).

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in all oceans
  • UNESCO-IOC Register of Marine Organisms
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Range

Occurs in tropical and subtropical waters worldwide, generally not ranging north of 40°N or south of 35°S (2) (5). Sightings of the pygmy killer whale have been most frequent in the eastern tropical Pacific, the Hawaiian Archipelago and off the coasts of Japan (2).
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Physical Description

Morphology

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

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Size

Length: 270 cm

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Size in North America

Sexual Dimorphism: Males may be longer than females.

Length:
Range: 2-2.6 m

Weight:
Average: 140 kg
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Ecology

Habitat

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

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Habitat and Ecology

Habitat and Ecology
The pygmy killer whale occurs in deep, warm waters, generally beyond the edge of the continental shelf, and rarely close to shore (except near some oceanic island groups where the water is deep and clear). This species is mainly tropical, but occasionally strays into warm temperate regions.

Little is known of the diet of this species, although it is known to eat fish and squid. It has occasionally been recorded attacking dolphins, at least those involved in tuna fishery interactions in the eastern tropical Pacific (Perryman and Foster 1980).

Systems
  • Marine
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Habitat Type: Marine

Comments: Widely distributed in tropical oceans.

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tropical and subtropical, oceanic
  • UNESCO-IOC Register of Marine Organisms
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Depth range based on 61 specimens in 1 taxon.
Water temperature and chemistry ranges based on 60 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 15.012 - 28.879
  Nitrate (umol/L): 0.045 - 7.309
  Salinity (PPS): 32.337 - 36.385
  Oxygen (ml/l): 4.595 - 5.969
  Phosphate (umol/l): 0.063 - 0.866
  Silicate (umol/l): 0.787 - 6.989

Graphical representation

Temperature range (°C): 15.012 - 28.879

Nitrate (umol/L): 0.045 - 7.309

Salinity (PPS): 32.337 - 36.385

Oxygen (ml/l): 4.595 - 5.969

Phosphate (umol/l): 0.063 - 0.866

Silicate (umol/l): 0.787 - 6.989
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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The pygmy killer whale inhabits deep, warm waters, and is rarely seen close to shore except around oceanic islands (6).
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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

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 )

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Comments: Reported to herd and attack other small cetaceans in the eastern tropical Pacific (see IUCN 1991).

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Associations

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:

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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:

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Known prey organisms

Feresa attenuata preys on:
Actinopterygii
Mollusca

This list may not be complete but is based on published studies.
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General Ecology

Commonly in herds of 50 or fewer individuals, sometimes up to several hundred (Leatherwood and Reeves 1983).

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Life History and Behavior

Behavior

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

  • Montie, E., C. Manire, D. Mann. 2011. Live CT imaging of sound reception anatomy and hearing measurements in the pygmy killer whale, Feresa attenuata. The Journal of Experimental Biology, 214: 945-955.
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Life Expectancy

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.

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Reproduction

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)

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Feresa attenuata

The following is a representative barcode sequence, the centroid of all available sequences for this species.


No available public DNA sequences.

Download FASTA File
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Statistics of barcoding coverage: Feresa attenuata

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 2
Specimens with Barcodes: 2
Species With Barcodes: 1
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Conservation

Conservation Status

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

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IUCN Red List Assessment


Red List Category
DD
Data Deficient

Red List Criteria

Version
3.1

Year Assessed
2008

Assessor/s
Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L.

Reviewer/s
Hammond, P.S. & Perrin, W.F. (Cetacean Red List Authority)

Contributor/s

Justification
This species is naturally uncommon. The combination of potential declines driven by impacts from high intensity anthropogenic sounds and bycatch in fisheries is believed sufficient that a 30% global reduction over three generations cannot be ruled out.

History
  • 1996
    Data Deficient
  • 1994
    Insufficiently Known
    (Groombridge 1994)
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National NatureServe Conservation Status

United States

Rounded National Status Rank: NU - Unrankable

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NatureServe Conservation Status

Rounded Global Status Rank: G4 - Apparently Secure

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Status

Classified as Data Deficient (DD) on the IUCN Red List 2007 (1), and listed on Appendix II of CITES (3).
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Population

Population
Although there is little information on the population biology of this species, the pygmy killer whale appears to be naturally uncommon. Wade and Gerrodette (1993) estimated that there were about 38,900 (CV=31%) of these whales in the eastern tropical Pacific. There are estimated to be 817 (CV=112%) in the Hawaiian portion of the US EEZ, and 408 (CV=60%) in the northern Gulf of Mexico (Barlow 2006; Mullin and Fulling 2004).

Population Trend
Unknown
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Threats

Major Threats
Because of their relatively low abundance, even small takes in localized areas could be significant. Although there is considerable controversy regarding the absolute level of declines, there is good evidence of large-scale reductions in many predatory fish populations (e.g., Baum et al. 2003, 2005; Sibert et al. 2006; Polacheck 2006) and over-fishing and collapse of several important “prey” fish stocks world-wide (e.g., Jackson et al. 2001). The effects of such fish population reductions and subsequent ecosystem changes on world-wide populations of pygmy killer whales are unknown but could result in population declines.

Predicted impacts of global climate change on the marine environment may affect pygmy killer whales, although the nature of impacts is unclear (Learmonth et al. 2006).

This species, like beaked whales, is likely to be vulnerable to loud anthropogenic sounds, such as those generated by navy sonar and seismic exploration (Cox et al. 2006) and have been a part of multi-species unusual stranding events in Taiwan (Wang and Yang, 2006).

Pygmy killer whales have been killed directly in both harpoon and driftnet fisheries (Caribbean islands, Sri Lanka, Taiwan and Indonesia) and incidentally in various types of fishing gear (most areas of the species’ range).

A few individuals are known to be taken in drives and in driftnets in various regions, most notably Japan and Sri Lanka (Ross and Leatherwood 1994). Reports on the small-cetacean fisheries of St Vincent and Lamalera suggest that pygmy killer whales form a very small proportion of the catch and that catches probably have little impact on the subpopulations in those areas. In Sri Lanka, there is mortality of this species due to harpooning of dolphins for use as bait on long-lines for sharks, billfish, and other oceanic fishes (Ross and Leatherwood 1994).

Although they comprise less than 2% of all cetaceans in monitored by-catches in gillnet fisheries in Trincomalee, Sri Lanka and in villages on the south-west coast of Sri Lanka, this may amount to 300 - 900 pygmy killer whales each year (Ross and Leatherwood 1994). The numbers of animals killed incidentally in net fisheries, such as those in Sri Lanka, may be much higher than is so far documented, because monitoring of these widespread activities is incomplete. In the long term, such takes may have a significant impact on pygmy killer whales where their distribution overlaps with extensive gillnetting operations (Ross and Leatherwood 1994). Small incidental catches are known in fisheries in other areas including the Philippines and Taiwan (Ross and Leatherwood 1994, Dolar 1994, J. Wang pers. comm. 2007).

Evidence from stranded individuals of several similar species indicates that they have swallowed discarded plastic items, which may eventually lead to death (e.g. Scott et al. 2001); this species may also be at risk.

This species does not appear to be particularly abundant anywhere that it has been sighted. In Hawaii, subpopulations appear to be small, and this, along with their limited movements, suggests the species may be particularly vulnerable to human impacts regionally.
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Comments: No known major threats (IUCN 1991).

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While the pygmy killer whale is not believed to be seriously threatened at present, its naturally low abundance means that even small takes could have a significant impact on local populations (7). Pygmy killer whales are captured intentionally in fisheries in St Vincent and Indonesia (2), where the whale meat may be consumed and the oil used for cooking and medicinal purposes (8), and in Sri Lanka, pygmy killer whales are harpooned and used as bait in long-line fisheries for sharks, billfish and other oceanic fishes. Pygmy killer whales are also caught incidentally in many areas (2).
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Management

Conservation Actions

Conservation Actions
The species is listed on Appendix II of CITES. Research is needed to determine the impact of potential threats on this species.
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Source: IUCN

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Conservation

The pygmy killer whale is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that any international trade in this species should be carefully regulated (3). There are not known to be any other measures in place at present to protect this enigmatic and intriguing ocean mammal.
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Relevance to Humans and Ecosystems

Benefits

Pgymy killer whales have no negative impact on humans.

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There are no known positive impacts of pygmy killer whales on humans.

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Economic Uses

Comments: No specific fishery for this species, though sometimes included among cetaceans driven ashore by Japanese fishermen (Leatherwood and Reeves 1983). Sometimes taken in general small cetacean fisheries in several parts of the range; used for human consumption and for oil for cooking and medicinal purposes (IUCN 1991).

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Risks

IUCN Red List Category

Data Deficient (DD)
  • IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
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Wikipedia

Pygmy killer whale

Pygmy killer whale!<-- This template has to be "warmed up" before it can be used, for some reason -->

The pygmy killer whale (Feresa attenuata) is a small, rarely-seen cetacean of the oceanic dolphin family (Delphinidae). It derives its common name from sharing some physical characteristics with the orca ("killer whale".) It is the smallest species that has "whale" in its common name. In fact, "killer" may be more apt in the case of the pygmy killer whale than its larger cousin. When a number of Pygmy Killers were brought into captivity in Hawaii and South Africa they were extremely aggressive—even killing one another. A pod captured in Japan did not display such aggression.

Until the early 1950s the pygmy killer whale was known only from two skulls kept at the British Museum. It had been described by John Gray in 1874. In 1954, Japanese cetologist Munesato Yamada published accounts of a "rare porpoise" discovered in 1952 by whale hunters working from Honshū. He wrote that the individuals he examined had skulls matching those in the museum and that the body had features similar to the killer whale, and proposed the common name lesser (or pygmy) killer whale. Despite its name and features, the pygmy killer whale is not closely related to the orca.

The scientific species descriptor attenuata is Latin for 'tapering' and refers to the gradual narrowing from the head to the tail fin.

Contents

Description

The pygmy killer is an average-sized dolphin (a little larger and heavier than a grown man) and may easily be confused at sea with other species, in particular the melon-headed whale. The body is robust and dark-colored. The cape is particularly dark. The head is rounded without a beak. The sides are lighter and the belly is often white. Several individuals have been seen with a white lining around the mouth and chin. The dorsal fin is tall and slightly falcate.

The pygmy avoids human contact. Some spy-hopping, breaching and other active behavior has been recorded but it is not an acrobatic animal.

These dolphins always move in groups, usually of 10 to 30, but occasionally much larger.

Data from strandings, which seem to be common in the species, indicates a diet of cephalopods and small fish. They have been observed attacking, killing and eating other cetacean species such as the Common Dolphin.

Population and distribution

The only population estimate is of 38,900 individuals in the eastern tropical Pacific Ocean.[1] However the species has a wide distribution in tropical and sub-tropical waters world-wide. They are sighted regularly off Hawaii and Japan. Appearance in bycatch suggest a year-round presence in the Indian Ocean near Sri Lanka and the Lesser Antilles. In the Atlantic individuals have been observed as far north as South Carolina on the west coast and Senegal on the east. The species is purely oceanic.


Footnotes

  1. ^ Whales, Dolphins and Porpoises, Mark Carwardine (1995) ISBN 0-7513-2781-6

References

  1. Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L. (2008). Feresa attenuata. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 24 March 2009. Database entry includes justification for why this species is listed as data deficient
  2. National Audubon Society: Guide to Marine Mammals of the World ISBN 0-375-41141-0
  3. Article Pygmy Killer Whale Meghan Donahue and Wayne Perryman pps 1009-1010 in Encyclopedia of Marine Mammals (1998) ISBN 0-12-551340-2
  4. Estimates of cetacean abundance and distribution in the eastern tropical Pacific P.R. Wade and T. Gerrodette (1993) Rep. Int. Whal. Comm. 43, 477-493


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