Overview

Brief Summary

Description

One of the largest and most distinctly marked of the beaked whales (5) (6) (7) (8), the strap-toothed whale is named for the unique and somewhat bizarre teeth of the adult male. In common with other beaked whales, only two teeth become well developed, one on each side of the lower jaw, but in the male strap-toothed whale these grow up and over the upper jaw, reaching to over 30 centimetres in length, and curling over the top of the jaw so that the mouth is clamped nearly shut (2) (3) (5) (7). Female and immature strap-toothed whales have no visible teeth, making them more difficult to distinguish from other beaked whale species (7) (9) (10). The body of the strap-toothed whale is robust and spindle-shaped, with a small dorsal fin about two-thirds of the way down the body, small flippers, and an unnotched tail fluke with pointed tips (7). Unusually, the species shows the reverse of typical cetacean colouration, being dark below and lighter above (8). The body is mainly black, with a white throat and upper back, white front to the beak, a white patch around the genital area, and a dark mask over the eyes and melon (3) (5) (6) (10). The pattern of light and dark areas is reported to be reversed in juveniles (10).
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Biology

Beaked whales are rarely seen in the wild and so very little is known about the biology of these elusive species (2). The strap-toothed whale may be solitary or occur in small groups of two to three individuals (5) (8) (12). The female gives birth to a single calf in spring or summer (5) (7), after a gestation period of around nine to twelve months (12), with the calf measuring about 2.2 metres at birth (7) (9). The diet of the strap-toothed whale is thought to comprise mainly squid, as well as some fish and crustaceans (11) (12) (13), and like other beaked whales it is believed to be a suction feeder, sucking prey into the mouth and swallowing it whole (2). The teeth of the male, not needed for feeding, have developed into weapons, with adult males often bearing scars from fights (2) (11). However, the adaptive significance of this species' unique tooth shape has never been fully explained (2), although it is not thought to hinder feeding, despite severely restricting the male's gape (12) (13).
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Strap-toothed, long-toothed or Layard's beaked whale (Mesoplodon layardii)

The common and scientific name honours Edgar Leopold Layard, who prepared drawings of a skull and sent them to John Edward Gray, who described the species in 1865 (Wikipedia).

The adult strap-toothed whale weighs 907-2,721 kg and is 5-6.2 m long (ADW), the largest member of the genus; the male is up to 5.9 m long and the female up to 6.2 m (J.Medby, Wikipedia). It has a robust, spindle-shaped body, with a rounded to slightly bulbous melon, which slopes steeply downward before merging with the fairly long, slender beak and straight mouthline, shortly before the strap teeth; a small, falcate dorsal fin about two-thirds of the way down the body; small, narrow, rounded flippers and an unnotched tail fluke with pointed tips. The front half of the rostrum and the dorsal region from posterior to the blowhole and anterior to the dorsal fin is light gray to white. This lighter coloration on the dorsal surface extends ventrally to the throat region via a narrow band that passes posterior to the eye. The body is mainly bluish-black to dark purplish, with patches of white on the underside, between the flippers and in a band around the head; there is a white throat and upper back, a white, cape-shaped area behind the head; white front to the beak, a white patch around the genital area and a black mask extends from the tooth back to the blowhole and encompasses the area immediately around the eye, through the angle of the mouth, and reduces to a narrow band across the chin, as well as covering the melon on the forehead. The flippers and remainder of the animal are black, with the anal region and posterior edge of the flukes the only other gray areas. The pattern of light and dark areas is reported to be reversed in juveniles, dark above and light below (ARKive, Wikipedia). Scars and cookie cutter shark bites are also present.

The male has a pair of well developed teeth, which full erupt from the gumline, one on each side of the lower jaw (mandible), back from the apex at 50 - 60% of total length of the mouthline. The strap-like teeth taper towards the tip. The denticle is on the outer side of the tooth, rather than the apex. The teeth are strongly inclined posteriorly at an approximate angle of 45 degrees. These grow up and over the upper jaw, reaching upto 75 cm in length and curling over the top of the jaw, so the mouth is clamped nearly shut, being only able to open 11-13 cm. The teeth have dorsally projecting denticles; barncles are often found on the teeth (Wikipedia). Teeth in females and juveniles do not erupt.

The whale seems to be widespread throughout deep, oceanic, cold, temperate to subantarctic waters of the Southern Hemisphere at latitudes of 30-60°S and a depth of up to 2,000 m beyond the edge of the continental shelf, far from shore (ARKive, Wikipedia). It may use adjacent waters for feeding and calving and there is some evidence of sexual segregation in distribution (J Medby). One individual breached between the South Orkney Islands and South Georgia (Wikipedia). Strandings have been recorded from South Africa, Australia, Tasmania, New Zealand, Argentina, Chile, Tierra del Fuego, the Falkland Islands, Uruguay, the Kerguelen Islands, Heard Island and Brazil (ADW, ARKive, IUCN). The seasonality of strandings suggests that the species may migrate (ARKive, J Medby). It may occur south of 38° S year-round moving north of 38° S seasonally (Wikipedia).

The whale may be solitary or occur in groups of two or three individuals (ARKive). The male's tusks may be a form of visual or tactile communication (ADW). The whale may use a form of accoustic communication (ADW).

It is thought to feed mainly on squid, as well as some fish and crustaceans (ADW, ARKive, IUCN). The male's teeth were thought to interfere with feeding, but may act as "guide rails" to send food to the throat (ADW), although the whale is believed to be a suction feeder, sucking prey into the mouth and swallowing it whole (ADW, ARKive). The male's teeth are not thought to hinder feeding, but severely restrict the gape, limiting the squid they can catch to 100 g and less (ARKive, Wikipedia). The whale's predators may include killer whales (ADW).

The teeth of adult whales have developed into weapons; males often bear a high number of scars from fights (ADW, ARKive, Wikipedia). The whale may breed each summer (ADW). The female gives birth to a single, probably precocial calf in spring or summer, after a gestation period of around 9-12 months (ADW, ARKive); the calf measures 2.2-3 m at birth (ADW, ARKive, J Medby, Wikipedia). Groups often consist of a single female with calf pairs (ADW). Calves follow the mother from birth. The female nurses the offspring.

The strap-toothed whale is listed on Appendix II of CITES (ADW, ARKive), so international trade in this species should be carefully monitored and controlled (ARKive). It is probably not rare compared to other beaked whales (ARKive, IUCN). Data is deificient, with no information on global abundance or trends in abundance (IUCN). It is not thought to be uncommon but it is potentially vulnerable to low-level threats (IUCN). It is threatened by entanglement in drift nets and other nets; competition from expanding longline fisheries; chemical pollution leading to accumulation of DDT and PCBs in body tissues and stranding (ADW, ARKive, IUCN). It may be vulnerable to loud anthropogenic sounds, such as those generated by navy sonar and seismic exploration (ARKive, IUCN); noise pollution has been linked to mass strandings of other beaked whale species (ARKive). It may be vulnerable to the effects of climate change; ocean warming may lead to a shift or contraction of the species range as it tracks the occurrence of its preferred water temperatures (ARKive, IUCN). It may die from swallowing discarded plastic items (ARKive, IUCN). The whale's preference for deep waters may have helped protect it from threats facing more coastal species (ARKive).

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Distribution

Mesoplodon layardii tends to live in the cold temperate waters of the Southern Hemisphere. A majority of the sightings have been around Australia, New Zealand, and Tasmania, but there have also been sightings in South Africa, Namibia, the Falkland Islands, Argentina, Chile, and Uruguay.

Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native )

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Range Description

Strap-toothed beaked whales apparently have a continuous distribution in cold temperate waters of the Southern Hemisphere, mostly between 35° and 60°S; there have been strandings in South Africa, Australia, Tasmania, New Zealand, the Kerguelen Islands, Heard Island, Argentina, Uruguay, Brazil, and the Falkland Islands (MacLeod et al. 2006). The seasonality of strandings suggests that this species may migrate. Like all beaked whales, they occur mostly in deep waters beyond the edge of the continental shelf. There is some evidence of sexual segregation in distribution.
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Range

The strap-toothed whale appears to be widespread throughout the cold temperate waters of the Southern Hemisphere, where it has been recorded mainly between latitudes of 35°S and 60°S. Strandings have been recorded from South Africa, Australia, Tasmania, New Zealand, Argentina, Chile, Tierra del Fuego, the Falkland Islands, Uruguay and Chile (1) (5) (11). The seasonality of strandings suggests that the species may migrate (1) (2) (12).
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Standing distribution

Stranding Distribution

Circumpolar distribution in the cold temperate waters of the southern oceans.

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Physical Description

Morphology

Adult strap-toothed whales weigh between 907 and 2,721 kg and are 5 to 6.2 m in length. Newborns tend to be 2.5 to 3 m in length,with and unknown weight.

These animals have a spindle-shaped body with a rounded to slightly bulging melon that ends in a long slender beak. The flippers are small, narrow, and rounded. The dorsal fin is set far past the body and is falcate in shape.

The whales are mainly bluish-black to dark purplish in color with patches of white on the underside, between the flippers, on the beak, and in a band around the head. There are also black patches over the eyes and forehead.

The most distinctive morphological characteristic of M. layardii is the single pair of mandibular teeth that are found only in adult males. These teeth curve over the upper jaw allowing the mouth to open only 11 to 13 cm. It is assumed that these teeth are used for intraspecific competition between males due to the high number of scars observed on the males.

Range mass: 907 to 2721 kg.

Range length: 5 to 6.2 m.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes shaped differently; ornamentation

  • MacLoed, C. 2000. Species Recognition as a Possible Function for Variations in Position and Shape of the Sexually Dimorphic Tusks of Mesoplodon Whales. Evolution, 54/6: 2171-2173. Accessed 12/03/02 at http://www.bioone.org.
  • The Whale and Dolphin Conservation Society. 2002. "The Whale and Dolphin Conservation Society" (On-line ). Accessed 11/04/02 at http://www.wdcs.org.
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Tooth morphology

Tooth position

A single pair of teeth are positioned back from the apex at 50 - 60% of total length of the mouthline. The strap-like teeth are strongly inclined posteriorly at an approximate angle of 45 degrees.

Tooth exposure

Teeth of adult males fully erupt from the gumline, reaching up to 30 in length, and may wrap around the dorsal rostrum, preventing the animal from opening its jaws.Teeth in females and juveniles do not erupt.

Tooth shape

The strap-like teeth taper towards the tip. The denticle is located on the outer side of the tooth, rather than the apex.

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Skull morphology

Diagnostic features of the skull and mandible

On the vertex of the dorsal skull the premaxillary bone extends forward of the nasal and frontal bones. Separates from Berardius and Ziphius.

A sulcus (groove) running along the middle of the combined surfaces of the nasal bones so depresses their combined middle that it is the lateral portion of each nasal bone that reaches farthest forward on the vertex. Separates from Tasmacetus and Indopacetus.

When the skull is upright and the long axis of the anterior half of the beak is horizontal, a horizontal plane transecting the summit of either maxillary prominence transects the mesethmoid bone. Separates from Hyperoodon.

Tooth alveoli of mandible overlap the posterior mandibular symphysis .Separates from M. densirostris, M. europaeus, M. ginkgodens, M. grayi, Mesoplodon hectori, Mesoplodon mirus, Mesoplodon perrini, M. peruvianus, and M. stejnegeri

Deep basirostral groove extends anteriorly well past the prominental turbercle. Separates from M. bidens, M. bowdoini, M. carlhubbsi, and M. traversii.

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External Morphology

Head Shape

The melon is moderately bulbous and slopes steeply downward before merging with the beak. The beak is long, slender with a straight mouthline.

Coloration

Males and females have similar pigmentation patterns. The front half of the rostrum and the dorsal region from posterior to the blowhole and anterior to the dorsal fin is light gray to white. This lighter coloration on the dorsal surface extends ventrally to the throat region via a narrow band that passes posterior to the eye. A black mask extends from the tooth back to the blowhole and encompasses the area immediately around the eye. This darker coloration extends through the angle of the mouth, and reduces to a narrow band across the chin. The flippers and remainder of the animal are black, with the anal region and posterior edge of the flukes the only other gray areas.

Size

Adult body length ranges between 5.2 to 6.2 m. Recorded maximum body length for adult males and females is 5.8 m and 6.2 m, respectively. Length at birth is 2.8 m.

Most Likely Confused With:

Mesoplodon grayi

Mesoplodon traversii

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Ecology

Habitat

cool temperate in Southern Hemisphere, oceanic
  • UNESCO-IOC Register of Marine Organisms
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Strap-toothed whales are found in deep oceanic waters of the temperate to subantartic regions. They may use adjacent waters for feeding and calving.

Range depth: 2000 (high) m.

Habitat Regions: saltwater or marine

Aquatic Biomes: pelagic

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Habitat and Ecology

Habitat and Ecology
Like all beaked whales, these whales occur mostly in deep waters beyond the edge of the continental shelf. The diet is comprised nearly entirely of oceanic squids, some occurring to great depths (Sekiguchi et al. 1996).

Systems
  • Marine
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Like other beaked whales, the strap-toothed whale occurs mainly in deep waters far from shore (1) (11) (12).
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Trophic Strategy

Twenty-four species of oceanic squid, along with some deep sea fish make up the main diet of strap-toothed whales. Confusion and fascination surround the feeding habits of these whales due to the enlarged mandibular teeth in the males. At first they were thought to interfere with feeding, but it is now thought that they may act as "guide rails" to send food to the throat. Even this hypothesis is questioned because it is quite possible that M. layardii, like other beaked whales, suck food into their mouths, regardless if how far they can open their mouths.

Animal Foods: fish; mollusks

Primary Diet: carnivore (Piscivore , Molluscivore )

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Associations

Strap-toothed whales feed on a variety of marine organisms. they are therefore likely to have some impact on populations of these organisms.

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These whales may be prey for killer whales.

Known Predators:

  • killer whales (Orcinus orca)

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Known predators

Mesoplodon layardii is prey of:
Orcinus orca

This list may not be complete but is based on published studies.
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Known prey organisms

Mesoplodon layardii preys on:
Actinopterygii
Mollusca

This list may not be complete but is based on published studies.
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Life History and Behavior

Behavior

The large tusks in adult males are presumably a form of visual or tactile communication. Other toothed whales also use echolocation. It is likely that there are some forms of accoustic communication within the species, also.

Communication Channels: visual ; tactile ; acoustic

Perception Channels: visual ; tactile ; acoustic ; echolocation ; chemical

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Life Expectancy

Lifespan of M. layardii is unknown. However, members of other species in the genus are reported to have lived from 27 to 48 years.

  • Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: The Johns Hopkins University Press.
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Reproduction

The mating system of M. layardii has not been observed.

Little is known about their reproductive behavior. It is thought that mating occurs in summer and calving occurs in summer to autumn after a 9 to 12 month gestation period.

Breeding interval: Strap-toothed whales breed once per year.

Breeding season: Breeding apparently occurs in the summer.

Average number of offspring: 1.

Range gestation period: 9 to 12 months.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous

There have been no studies of parental care in M. layardii. However, groups consisiting of a single female with calf pairs are often observed. In general, newborn cetaceans are precocial. They are able to follow the mother from birth. Although the female nurses the offspring, the duration of lactation is not known for this species. The role of the male in parental care is likewize unknown.

Parental Investment: no parental involvement; precocial ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Protecting: Female)

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Conservation

Conservation Status

Mesoplodon layardii is a species which is threatened by many things: possible entanglement in drift nets and other nets; competition from expanding fisheries, especially on squids; pollution leading to accumulation of DDT and PCBs in body tissues; and they are the most stranded Ziphiid in Australia. In 1982, the National Stranding Contigency Plan was designed to outline scientific objectives and appropriate biological/veterinary research activies for the stranded whales.

Another focus for the conservation efforts lies in the development of objectives and agreements to protect cetaceans and their environment under federal and state laws. Strap-toothed whales are listed on Appendix II of CITES.

US Federal List: no special status

CITES: appendix ii

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
There is no information on global abundance or trends in abundance for this species. It is not believed to be uncommon but it is potentially vulnerable to low-level threats and a 30% global reduction over three generations cannot be ruled out (criterion A).

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

Classified as Data Deficient (DD) on the IUCN Red List (1) and listed on Appendix II of CITES (4).
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Population

Population
There is little information available on the status of the strap-toothed whale, but based on the number of strandings, it is probably not a rare species compared to its congeners.

There is no information on trends in the global abundance of this species.

Population Trend
Unknown
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Threats

Major Threats
Direct hunting has never been associated with this species. Pervasive gillnet and longline fisheries throughout the species' range raises concern that some bycatch is likely. Even low levels of bycatch might cause unsustainable impacts on this group of naturally rare cetaceans.

This species, like other 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).

As a cold to temperate water species, the strap-toothed whale may be vulnerable to the effects of climate change as ocean warming may result in a shift or contraction of the species range as it tracks the occurrence of its preferred water temperatures (Learmonth et al. 2006). The effect of such changes in range size or position on this species is unknown.

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.

Predicted impacts of global climate change on the marine environment may affect this species of whale, although the nature of impacts is unclear (Learmonth et al. 2006).
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The strap-toothed whale is thought to be relatively common (7), but a lack of information on its global abundance or population trends makes it difficult to assess its conservation status (1) (3). However, beaked whales appear to have naturally quite low populations, meaning even low-level threats can have unsustainable impacts (1). The strap-toothed whale is not directly hunted, although some bycatch in gillnets and longline fisheries is likely (1) (5) (12) (14). Other threats may include noise pollution, which has been linked to mass strandings of other beaked whale species, as well as chemical pollution, ingestion of plastic waste, and ocean warming as a result of climate change (1) (3) (12) (14). The strap-toothed whale's preference for deep waters may have helped protect it in the past from the threats facing more coastal species (3), but as fisheries expand into deeper waters the species may face increasing competition for its squid prey, and an increased threat from entanglement in nets (3) (12).
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Management

Conservation Actions

Conservation Actions
The species is listed in Appendix II of CITES. Research is needed to determine the impacts of potential threatening processes on this species.
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Conservation

The strap-toothed whale is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning international trade in this species should be carefully monitored and controlled (4). Research is needed to determine the impacts of the threats to the strap-toothed whale, in addition to further investigating its biology, seasonal movements and population trends (1) (12). International efforts may be needed to control current and potential threats to the species, in particular the development of fisheries directed at its deep-sea squid prey (12).
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Relevance to Humans and Ecosystems

Benefits

These animals are not reported to have any negative impacts on humans.

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These animals are not reported to have any positive economic impact on humans.

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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

Strap-toothed whale

The strap-toothed whale (Mesoplodon layardii), also known as the Layard's beaked whale or the long-toothed whale is a large mesoplodont with some of the most bizarre teeth of any mammal. The common and scientific name was given in honor of Edgar Leopold Layard, the curator of the South African Museum who prepared drawings of a skull and sent them to the British taxonomist John Edward Gray, who described the species in 1865.[2]

Description[edit]

Skull

The overall body shape of the strap-toothed whale is fairly typical for a mesoplodont, except for the large size. Male specimens have large and peculiar teeth even for the genus; the teeth emerge from the lower jaw and grow upward and back at a 45 degree angle to encircle the upper jaw and nearly close it. These teeth can sometimes grow to over 30 centimetres (0.98 ft) in length. The teeth have dorsally projecting denticles, and are apparently used for fighting. Barnacles are frequently found on the teeth, as well. Why the species would grow teeth that severely cut back on the size of prey it can consume is uncertain. The melon is somewhat bulbous, and blends into the beak shortly before the strap teeth. The beak itself is fairly long, with a relatively straight mouthline. The coloration of this species is also unusual for a mesoplodont, since it is rather bold; most of the body is black except for a white areas on the front of the beak, the throat, an area behind the head in a shape reminiscent of a cape, and near the genitals. Juveniles do not have this coloration and are typically countershaded, dark above and light below. Scars and cookie cutter shark bites are also present. Males can reach around 5.9 metres (19 ft), whereas females reach 6.2 metres (20 ft) and likely weigh around 1,000–1,300 kilograms (2,200–2,900 lb), indicating they are probably the largest species in the genus. Newborn calves may be up to 2.8 metres (9.2 ft) in length.

Population and distribution[edit]

The Strap-toothed whale is distributed in cool temperate waters of the Southern Hemisphere between 30°S and the Antarctic Convergence. It may occur south of 38°S year-round moving north of 38°S seasonally.[3] As of 1991, there are about 140 records (nearly all strandings) of this species from New Zealand (50, including one sighting), Australia (over 40), southern Africa (about 40), southern Argentina and Tierra del Fuego (10), southern Chile (4), Falkland Islands (3), and Uruguay (1).[4] Strandings have also been reported from Heard Island, the Kerguelen Islands, and Brazil. More recently[when?] one individual was seen breaching between the South Orkney Islands and South Georgia.[5]

Behaviour[edit]

Strap-toothed whales' diet consists primarily of squid. Adult males have a gape half the size of females and juveniles, limiting their squid to those weighing 100 grams (3.5 oz) and less. Nothing is known about social organization of this species.

Conservation[edit]

This species has never been hunted or entangled in fishing gear. It is believed to be in a rather safe position compared with other mesoplodonts. Layard's beaked whale is 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)[6] and the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU).[7]

References[edit]

  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). Mesoplodon layardii. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 24 March 2009. Database entry includes a brief justification of why this species is of data deficient
  2. ^ Reeves, R., Stewart, B., Clapham, P. & Powell, J. (2002). Guide to Marine Mammals of the World. New York: A.A. Knopf. p. 292. ISBN 0-375-41141-0. 
  3. ^ Shirihai, H. and Jarrett, B. (2006). Whales, Dolphins and Other Marine Mammals of the World. Princeton Field Guides. p. 142. ISBN 0-691-12757-3. OCLC 73174536. 
  4. ^ Klinowska, M. (1991). Dolphins, Porpoises and Whales of the World: The IUCN Red Data Book. Cambridge, U.K.: IUCN. 
  5. ^ Jefferson, Thomas; Webber, Marc A.; Pitman, Robert L. (2008). Marine Mammals of the World: A Comprehensive Guide to their Identification. London: Academic. 
  6. ^ Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia
  7. ^ Official webpage of the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region
  • Encyclopedia of Marine Mammals. Edited by William F. Perrin, Bernd Wursig, and J.G.M Thewissen. Academic Press, 2002. ISBN 0-12-551340-2
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