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Hexanchus griseus are mainly deepwater sharks with shy demeanors. Opportunities to study live specimens are few and far between. Bluntnose sixgill sharks kept in captivity suffer from stress due to their light-sensitive eyes and their large size.

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
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Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Behavior

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Hexanchus griseus are believed to have few forms of communication, as they seem to be solitary animals for the most part. Yet any social forms of communication that do exist between these animals are unknown. The only known form of communication to occur in H. griseus is during mating. The males are believed to use their teeth to entice the females into mating. These sharks are equipped with highly sensitive scent and visual organs, which are useful for perceiving the dark environment they live in. H. griseus is also able to detect other organisms by means of its lateral line system (used for detecting vibrations), and its ampullae of Lorenzini (which detect faint electric signals).

Communication Channels: visual ; tactile

Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical ; electric

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
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Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Conservation Status

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Fishermen are killing H. griseus for sport and for food (as they are being more frequently spotted in fishing areas) faster than ever before. Because of their low reproductive rate, sixgill sharks can easily be over-harvested. There are new regulations being enacted prohibiting the recreational killing of these sharks. The IUCN rates this species as "Lower Risk/Near Threatened", and notes that the lack of population data means that this species could be in more trouble than we know.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: near threatened

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
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Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Life Cycle

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Little is yet known about the life cycle and fetal development of Hexanchus griseus.

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Benefits

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Despite their size, these sharks are not considered much of a direct threat to humans. They are described as shy, nonagressive animals that pose no threat to humans unless physically provoked. Also, their preference for deep water and darkness makes human encounters with this species relatively rare.

Some medical professionals consider the liver of Hexanchus griseus to be toxic, as its ingestion has been known to cause painful sickness for up to 10 days. The skin of H. griseus has also been known to cause such sickness.

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
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Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Benefits

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This species is killed for food, harvested with line gear, gill nets, and other equipment. It is also caught by game fishermen.

Since they are large and widespread animals, these sharkes they may have a significant role in deep-water fisheries, but we have no information on this.

Positive Impacts: food

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Associations

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This species is a large, deep-water predator, but we have little information on its ecological effects. There is some evidence that Hexanchus griseus has an important impact on the white sharks' population off the coast of South Africa. Researchers there believe that H. griseus will eventually outcompete Carcharodon carcharias in that area. H. griseus is not known to participate in any symbiotic relationships.

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Trophic Strategy

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Hexanchus griseus is a skilled predator and is solely carnivorous, feeding on such animals as fishes, rays, and other sharks. Although they have been reported as being sluggish in nature, their body structure enables them to reach remarkable speeds for chasing and effectively capturing prey. Aside from feeding on molluscs and marine mammals, they eat crustaceans (crabs and shrimp), agnathans (Hagfish and sea lampreys), chondrichthyans (ratfish) and teleosts (dolphinfish and lingcod). A subspecies of H. griseus living in Cuban waters is also a skilled scavenger that feeds on carcasses of mammals.

Animal Foods: mammals; fish; carrion ; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore , Eats non-insect arthropods, Molluscivore )

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Distribution

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Hexanchus griseus occur globally in all oceans. These sharks live and thrive in the most widespread distribution of all known sharks, with the possible exception of white sharks.

Biogeographic Regions: indian ocean; atlantic ocean ; pacific ocean ; mediterranean sea

Other Geographic Terms: cosmopolitan

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Habitat

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Hexanchus griseus is mainly a deep water shark, rarely found at depths of less than 100 m. The species seems to usually stay close to the bottom, near rocky reefs or soft sediments. The deepest one has been found was about 2500 m.

These sharks are diel vertical migrators; they are nocturnal and remain in the deep oceans during the day but rise towards the surface at night. Hexanchus griseus also seasonally migrates to shallower coastal waters. During the warmer months of the year, these sharks can occasionally be found in shallower waters at depths of 23 to 39 m during the day and as shallow as 3 m at night.

Range depth: 3 to 2,500 m.

Habitat Regions: temperate ; tropical ; saltwater or marine

Aquatic Biomes: benthic ; coastal

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
author
Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Life Expectancy

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There is little information available about the lifespan of Hexanchus griseus. These sharks have a life expectancy no longer than 80 years in the wild. There is some suggestion that because they have such high infant birth rates, mortality rates could be very high as well. There is no known record for the oldest bluntnose sixgill shark in the wild, and this species has not been excessively studied or maintained in captivity, so there is no information on its lifespan in captivity. A new study is available, however, regarding the age determination of H. griseus. Previous techniques used in determining the age of H. griseus have been unsuccessful because of its poorly calcified vertebral centra (a characteristic of deep-water species and of primative families). This new study indicates that examining the neural arches on the fins of H. griseus can be useful in determining the age of this particular shark.

Average lifespan
Status: wild:
about 80 years.

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Morphology

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Hexanchus griseus is characteristically a large shark species with a heavy build. These sharks have a short, blunt snout, a broadly rounded mouth, and six pairs of gill slits (from which its common name, the bluntnose sixgill, is derived). They have large, green eyes and broad comb-like teeth on each side of the lower jaw arranged in 6 rows. Their coloring shades varies from grayish-black to chocolate brown on the dorsal surface and lightens to grayish-white on its belly. There is an anal fin, and one dorsal fin located on the back end of the body. The caudal fin is slightly raised so that the lower lobe is lined up with the body axis. The pelvic fins are located to the anterior of the anal fin and are a bit larger. Like many benthic sharks, the caudal fin of Hexanchus griseus has a weakly developed lower lobe. However, the bluntnose sixgill shark is still a very strong swimmer.

There exist size differences between male and female sharks. Females tend to be slightly larger than males, averaging around 4.3 m in length while males tend to stay near 3.4 m. There is little or no color difference between the sexes; however, the seasonal scars appearing on the fins of females, which are believed to be a result of mating, are commonly used for sex identification. Sex can be easily determined by the presence of elongate claspers on the pelvic fins of male sharks. The bluntnose sixgilled shark is classified under the genus Hexanchus with only one other species, Hexanchus nakamurai, or the bigeyed sixgill shark. Both sharks are similar in all aspects aside from their unmistakable size difference. While H. nakamurai reaches only about 2.3 m in length, H. griseus reaches lengths of 4.8 m.

Range mass: 480 to 720 kg.

Average mass: 500 kg.

Range length: 3.5 to 4.8 m.

Average length: 3.7 m.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: female larger

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Associations

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Hexanchus griseus has no known evolved anti-predator adaptations. These sharks, however, are equipped with very sensitive perception organs, which may allow them to detect potential predators. The retinas are comprised of mostly rods and, therefore, do not function well in even moderately lit areas but are well suited for the dark conditions of the deep oceans. Being such a large-bodied shark, its only real predators would be other big sharks, such as whites, or possibly orca whales, which are known to prey on adult sharks. Young H. griseus have been taken by sharks, whales, dolphins, and sea lions.

Known Predators:

  • Steller's sea lions (Eumetopias jubatus)
  • great white sharks (Carcharodon carcharias)
  • killer whales (Orcinus orca)
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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Reproduction

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Very little is known about these sharks in terms of their social behavior and thus little is known about their mating systems. There are a few theories, however, attempting to explain how H. griseus mates. Researchers believe that the morphology of the teeth of H. griseus play an important role in mating. The male has a more erect primary cusp than do the females. The male is believed to nip the female's gills with this cusp in order to catch her attention and entice her into mating. Evidence supporting this idea of courtship is evident by the seasonal scars that appear on females every year presumably from being nipped by males. Bluntnose sixgill sharks are believed to be primarily solitary animals and there is no information indicating whether they prefer one or many mates.

There is not much information pertaining to the reproductive behavior of Hexanchus griseus; however, there is some hypothetical information available. These sharks are believed to meet seasonally, moving to shallower depths in the May to November months. Scientists are unsure of the bluntnose sixgill shark's gestation period, but it is thought to be longer than 2 years. The means of reproduction for these sharks is ovoviviparity, meaning they carry their eggs internally until they hatch. Babies develop within the mother without a placenta to provide nourishment, and they are born at a fairly mature size (generally 70 cm at birth). Each litter can number from about 22 to 108 pups and this incredibly large litter size for H. griseus could suggest that mortality rates for the pups are very high. Little is known about their maturation because until recently determining their age was difficult as a result of their poorly calcified vertebrae. The pups of H. griseus, however, are speculated to mature around 11 to 14 years for males and 18 to 35 years for females. Little else is known about its reproductive system.

Breeding season: May - November.

Range number of offspring: 22 to 108.

Range age at sexual or reproductive maturity (female): 18 to 35 years.

Range age at sexual or reproductive maturity (male): 11 to 14 years.

Key Reproductive Features: seasonal breeding ; sexual ; fertilization (Internal ); ovoviviparous

There is no information available pertaining to parental care for Hexanchus griseus. However, as with other sharks, it can be assumed that no parental care is given to the young, which can number up to 108.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)

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Bauml, J. 2004. "Hexanchus griseus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hexanchus_griseus.html
author
Jessica Bauml, University of Michigan-Ann Arbor
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Phil Myers, Museum of Zoology, University of Michigan-Ann Arbor
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David Armitage, Animal Diversity Web
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George Hammond, Animal Diversity Web
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Biology

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Very little is known about this shark's social and mating behaviour, but they are thought to be solitary, coming together only to mate. Males are believed to nip a female's fins to entice her into mating (2). Reproduction in this shark is ovoviviparous; the young hatch from eggs retained within the mother so that she then gives birth to live young (2) (3). The exact gestation period is unknown, but it is thought to be longer than two years. Each litter can number from 22 to 108 pups and this incredibly large litter size suggests that juvenile mortality rates are high (2). Age determination is difficult in this species but males are believed to mature at 11 to 14 years, females at 18 to 35 years, and longevity to reach 80 years for both sexes (3). The bluntnose six-gill shark is a skilled predator and may also scavenge, feeding nocturnally on a wide variety of marine organisms including other sharks, rays, bony fishes, squid, crabs, and seals (1) (2). Although reported as being sluggish in nature, they can reach remarkable speeds when chasing prey (2).
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Conservation

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As the bluntnose six-gill shark is relatively widespread and abundant, there is no legislation against the commercial fishing of this species. There are, however, new regulations being enacted prohibiting the recreational killing of these sharks in some areas of its range (2). The Food and Agriculture Organisation of the United Nations (FAO) have been working on an International Plan of Action for the conservation and management of sharks throughout the world (IPOA-SHARKS) (6), but the lack of sufficient population data on these sharks makes developing appropriate conservation management plans extremely difficult. Furthermore, being mainly deepwater sharks with shy demeanours, opportunities to study live specimens are rare (2). Thus, data on population numbers and distribution is urgently needed to enable this reclusive shark to be effectively monitored and protected.
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Description

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As its common name alludes, the bluntnose six-gill shark has a characteristically blunt rounded snout and six long gill slits on either side of its head, instead of the five that are usual amongst sharks (2). Other distinguishing features include its fluorescent green eyes, six saw-like teeth on each side of the lower jaw and the singular dorsal fin located close to the caudal fin (3). Colouring ranges from greyish-black to chocolate brown on the back, lightening to a greyish white underside, with a distinctive light stripe along the sides and white edging on the fins (4). Females tend to be slightly larger than males (2).
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Habitat

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A reclusive deepwater species, found in the waters of continental and insular shelves and upper slopes (4). Juveniles may be found closer inshore while adults occupy deeper waters (1). This shark rests along the bottom during the day to depths of 2,000 meters, swimming close to the surface at night to feed (4).
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Range

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The bluntnose six-gill shark is one of the wider ranging sharks, occupying temperate and tropical seas around the world (3).
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Status

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Classified as Lower Risk/near threatened (LR/nt) on the IUCN Red List (1).
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Threats

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The bluntnose six-gill shark is fished commercially and as a game fish throughout its range (3). However, the species seems unable to sustain target fisheries and is more usually taken as bycatch (1). The flesh is sold fresh, frozen and dried-salted for consumption, and is also utilised for oil and fishmeal (5). In parts of its range, including the Northeast Pacific, regional populations have depleted so much from fishing that they would be better classified as Vulnerable (A1bd+2bd) (1). Because of their relatively low reproductive rate these sharks are slow to rebound if over fished (2).
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Diagnostic Description

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A heavily-bodied, broad-headed sixgill shark, mouth ventral with 6 rows of lower, bladelike, comb-shaped teeth on each side (Ref. 247). Snout broadly rounded, body fusiform (Ref. 6871). Anal fin smaller than dorsal fin (Ref. 6871). Brown or grey above, paler below, with a light stripe along side (Ref. 26346). Fins with white edges (Ref. 6574). Live specimens with fluorescent green eyes (Ref. 6871). Six gill slits are very long (Ref. 35388).
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Recorder
Cristina V. Garilao
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Life Cycle

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Ovoviviparous, litters very large, 22 to 108 (Ref. 247). Size at birth 60-75 cm (Ref. 26346). Distinct pairing with embrace (Ref. 205).
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Recorder
Estelita Emily Capuli
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Migration

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Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.
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Kent E. Carpenter
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Morphology

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Dorsal spines (total): 0; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0
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Cristina V. Garilao
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Trophic Strategy

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Depth range reported at 0m-2000m. A deepwater species of the outer continental and insular shelves and upper slopes (Ref. 6871, 75154). Near bottom, occasionally pelagic, adults usually below 91 m (Ref. 58302). Juveniles may be found close inshore (Ref. 6871). Found on the bottom by day, moving to the surface at night to feed, and where it may take longlines set for other species (Ref. 45445). Depth distribution related to growth and temperature, with juveniles having most shallow records and from colder, poleward regions (Ref. 58302). Feeds on a wide range of marine organisms, including other sharks, rays, chimaeras, bony fish, squids, crabs, shrimps, carrion, and even seals. Is a eurytrophic predator that is capable of exploiting a wide range of prey species and habitats (Ref. 26969). A vertical migrant, it may sit on the bottom by day, and rise to the surface at night to feed (Ref. 247).
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Recorder
Estelita Emily Capuli
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Biology

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Depth range reported at 0m-2000m. A deepwater species of the outer continental and insular shelves and upper slopes (Ref. 6871). Near bottom, occasionally pelagic, adults usually below 91 m (Ref. 58302). Juveniles may be found close inshore (Ref. 6871). Found on the bottom by day, moving to the surface at night to feed, and where it may take longlines set for other species (Ref. 45445). Depth distribution related to growth and temperature, with juveniles having most shallow records and from colder, poleward regions (Ref. 58302). Feeds on a wide range of marine organisms, including other sharks, rays, chimaeras, bony fish, squids, crabs, shrimps, carrion, and even seals. Ovoviviparous (Ref. 205), with 22 to 108 pups in a litter (Ref. 247). Marketed fresh, frozen, or dried salted; also utilized as a source of oil and fishmeal. Not known to have attacked people without provocation (Ref. 247). Give birth to almost 100 young (Ref. 35388).
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Kent E. Carpenter
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Importance

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fisheries: commercial; gamefish: yes
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Kent E. Carpenter
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分布

provided by The Fish Database of Taiwan
廣泛分布於世界各溫帶及熱帶海域。臺灣東北部海域曾發現。
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臺灣魚類資料庫
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臺灣魚類資料庫

利用

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主要以底拖網、流刺網及鏢旗魚法捕獲,經濟價值高。肉質佳,魚肉紅燒或加工成各種肉製品;鰭可做魚翅;皮厚可加工成皮革;肝可加工製成魚肝油;剩餘物製成魚粉。
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描述

provided by The Fish Database of Taiwan
體延長,前部稍粗大。頭寬扁;尾基上下方無凹窪。吻短而鈍。眼大,卵圓形,無瞬膜。鼻孔小,近於吻端。口裂寬,弧形;上下唇褶不甚發達。兩頜齒異形;上頜無正中齒,每側20個,前面2齒簡單而細尖,齒頭外斜,中間8-9齒,外側具1-3小齒頭,最後7齒低小圓形,齒頭很小或無;下頜正中具一齒,中央齒頭尖長,側齒頭3,每側12齒,前面6齒寬扁長方形,具7-10小齒頭,後面6齒細小。噴水孔細小,位於眼後緣上方。鰓孔6個。背鰭一個,小而後位,起點與腹鰭後端上方,後緣凹入,上角鈍圓,下角尖突;胸鰭寬大,鐮刀狀,後緣凹入,外角鈍尖,內角鈍圓;尾鰭狹長,尾椎軸稍翹,上葉見於尾端,下葉前部具顯著三角形突出,中、後部間具缺刻。體背側暗褐色;吻腹側及腹部淡色;各鰭灰褐色;尾鰭下葉及末端灰黑色。
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棲地

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棲息於大陸棚或島嶼棚斜坡外緣的近、外海底棲大型鯊類,一般棲息深度在180-1,100公尺附近,但最深可達2,000公尺,具日夜垂直分布,白天棲於底層,晚上至上層覓食。主要以其它小型鮫類、小型硬骨魚類、甲殼類及烏賊等為食。卵胎生,一胎可產下約22-108尾幼鯊,剛出生之幼鯊體長可達60-70公分。
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Bluntnose sixgill shark

provided by wikipedia EN

The bluntnose sixgill shark (Hexanchus griseus), often simply called the cow shark, is the largest hexanchoid shark, growing to 20 ft (6.1 m) in length.[2] It is found in tropical and temperate waters worldwide and its diet is widely varied by region. The bluntnose sixgill is a species of sixgill sharks, of genus Hexanchus, a genus that also consists of two other species: the bigeye sixgill shark (Hexanchus nakamurai) and the Atlantic sixgill shark (Hexanchus vitulus). Through their base pairs of mitochondrial genes COI and ND2, these three species of sixgills widely differ from one another.[3]

Taxonomy

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1877 drawing of the bluntnose sixgill shark

The first scientific description of the bluntnose sixgill shark was authored in 1788 by Pierre Joseph Bonnaterre. As a member of the family Hexanchidae, it has more close relatives in the fossil record than living relatives. The related living species include the dogfish, the Greenland shark, and other six- and seven-gilled sharks. Some of the shark's relatives date back 200 million years. This shark is a notable species due to both its primitive and current physical characteristics.

Description

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The bluntnose sixgill shark is one of three shark species that have six gill pairs. Other two are - Frilled shark (Chlamydoselachus anguineus) and Bigeyed sixgill shark (Hexanchus nakamurai)[4]

The bluntnose sixgill shark has a large body and long tail. The snout is blunt and wide, and its eyes are small. There are 6 rows of saw-like teeth on its lower jaw and smaller teeth on its upper jaw.[4] Skin color ranges from tan, through brown, to black. It has a light-colored lateral line down the sides and on the fins' edges, and darker colored spots on the sides. They also get stains/spots on their neural arches, and the number of stains increase as they get older.[5] Its pupils are black and its eye color is a fluorescent blue-green. The bluntnose sixgill shark can grow to 5.5 m (18 ft),[6]. A work from the 1880s stated that a bluntnose sixgill shark caught off Portugal in 1846 measured 8 m (26.5 ft). This specimen was originally reported in an 1846 work and said to be only 0.68 m (2.3 ft) long.[7] Adult males generally average between 3.1 and 3.3 m (10 and 11 ft), while adult females average between 3.5 and 4.2 m (11 and 14 ft). The average weight of an adult bluntnose sixgill shark is 500 kilograms (1102 lbs).

The bluntnose sixgill shark resembles many of the fossil sharks from the Triassic period. A greater number of Hexanchus relatives occur in the fossil record than are alive today. They have one dorsal fin located near the caudal fin. The pectoral fins are broad, with rounded edges. The six gill slits give the shark its name. Most common sharks today only have five gill slits.

Growth and development

In general, the size (in length and weight) of the sixgills increase with maturity. With the male sharks specifically, their sexual maturity is usually determined by the length of their claspers. While juveniles have short and flexible ones, mature male sixgills have rigid, calcified longer ones.[8] On the other hand, the length-weight relationship of females tend to increase very rapidly as they get to the onset of their sexual maturity.[9]

Distribution and habitat

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The bluntnose sixgill is often found near the ocean floor.

With a global distribution in tropical and temperate waters, the bluntnose sixgill shark is found in a latitudinal range between 65°N and 48°S in the Atlantic, Indian, and Pacific oceans.[10] It has been seen off the coasts of North and South America from North Carolina to Argentina and Alaska to Chile. In the eastern Atlantic, it has been caught from Iceland to Namibia, in the Indo-Pacific it has been caught from Madagascar north to Japan and east to Hawaii[11] and in the Mediterranean it has been caught in Greece and Malta.[12] It typically swims near the ocean floor or in the water column over the continental shelf in poorly lit waters.[4] It is usually found 180–1,100 m (590–3,610 ft) from the surface, inhabiting the outer continental shelf, but its depth range can extend from 0–2,500 m (0–8,202 ft).[11][13][14] Juveniles will swim near the shoreline in search of food, sometimes in water as shallow as 12 m (39 ft), but adults typically stay at depths greater than 100 m (330 ft). It can be seen near the ocean's surface only at night.[4]

An adult bluntnose sixgill shark was recently seen at a depth of 259 m (854.7 ft) in the Philippines, for example. On December 2, 2017, the ROV camera of Paul Allen's research vessel RV Petrel captured video footage of the shark lurking around a World War II shipwreck in Ormoc Bay. This was the first time the species was photographed in Philippine waters.[15] In 2018, a sixgill shark was filmed near the Saint Peter and Saint Paul Archipelago, midway between Brazil and Africa, at a depth of around 400 feet.[16] In 2019, the remains of a pregnant bluntnose sixgill shark were found on a Vancouver Island beach, north of Victoria, British Columbia.[17] On 18 October 2019, a large bluntnose sixgill shark measuring over 3 meters and weighing 900 kg was found dead on the beach at Urkmez beach in Seferihisar, Izmir, Turkey.

Being in such a deep area of the ocean, these sharks have developed the behavior of undergoing diel vertical migration in order to have more access to food. Research has found that it takes more time for the sixgills to have to swim back down to their natural habitat of the bathypelagic rather than to swim up during the night to find food in the more populated zones. As such, it can be inferred that they have some sort of adaptation that aids buoyancy to ensure that these sharks are able to float more easily.[18] An example of this DVM occurrence was found off the coast of Oahu, Hawaii, whereby 4 sixgills' behaviors were studied. At around midnight to 3am, the 4 sharks swam up to a minimum depth of 300m whereas at about noon, they reached their maximum depth of between 600 to 700m.[19] This shows a daily pattern whereby the sixgills are going up during the nights when it is darker and colder to forage for food up in the shallower depths but as morning comes and light and higher temperatures starts to come in more intently again, the sharks go back down to their original habitat to maintain a lower metabolic rate, ensuring that they will be able to use the nutrients from whatever they ate during the night slowly, reducing the need for them to search for more food throughout the day. Another study found that the motivating factor for the bluntnose sixgill sharks' DVM behavior was foraging. Researchers were able to rule out predator and competitor avoidance as potential reasons for the vertical movement patterns because they found pairs of sharks with synchronized movements, indicating that the sharks were responding to the same stimuli. The sharks demonstrated distinct and consistent patterns of vertical migration despite size, sex, and spatial scales, showing that foraging behavior can most likely be seen as the reason for the diel vertical patterns of sixgill sharks.[20] Lastly, the bluntnose sixgill shark has consistent seasonal movements. They move north during the winter and spring and south during the summer and fall. In this study as well, researchers were able to determine that these movement patterns can be attributed to the seasonal movements of prey over other reasons.[21]

Feeding behavior

Feeding behavior of the sixgills

Sixgill sharks possess variability in their feeding mechanisms that could have contributed to their evolutionary success and global distribution. These sharks are able to protrude their jaws and vary their methods of feeding depending on the situation. They utilize sawing and lateral tearing techniques to manipulate food. Sixgill sharks also lower their pectoral fins right before they strike in order to stop forward progressions, making it easier for them to forage.[22]

Biology and ecology

Although sluggish in nature, the bluntnose sixgill shark is capable of attaining high speeds for chasing and catching its prey using its powerful tail. Because of its broad range, it has a wide variety of prey, including fish, rays, chimaeras, squid, crabs, shrimps, seals, and other (smaller) sharks.[11] The bluntnose sixgill shark is therefore classified as a generalist species, and is less likely to be affected by scarcity in any one of its food sources.[23] A study done in 1986, with 28 sixgills, discovered that the most abundant meal they were able to obtain include cartilaginous and bony fishes, followed by marine mammals and several invertebrates.[24] As time passes, however, it seems that their stomach contents have changed. In 1994, it was found that of 137 samples, the major prey groups were cephalopods, teleost fishes, chondrichthyans and marine mammals.[25] This difference in results could be due to several reasons. Firstly, as noticed in the different sample sizes of the two studies, it could be due to technology back then not being advanced enough to fully study the stomach contents and capture enough samples, leading to a skewed result for the 1986 study. Next, as human activities have increased over the years, it could affect the availability of food for the sixgills in the deep. There are other potential reasons for this change in diet, many factors may have affected the sixgills.

Bluntnose sixgill sharks are also positively buoyant as hypothesized earlier. During vertical movements, the sixgill sharks demonstrate more swimming efforts for the descent than the ascent. This is indicated by the greater number of tail beats and the sharks' ability to glide upwards for several minutes. The positive buoyancy can help the sharks to hunt stealthily by approaching prey from below undetected since the upward gliding permits minimal movement. It can also be advantageous for their diel vertical migrations. Since the sharks spend their days in colder water, their metabolic rates decline. Positive buoyancy can help them to glide upwards with minimal swimming involved during their evening migrations.[26]

Reproduction is ovoviviparous with embryos receiving nourishment from a yolk sac while remaining inside the mother. Litters are large and typically have 22-108 pups measuring 60–75 cm (24–30 in) at birth,[11] and the largest recorded pup is 82 centimetres (32 in). New pups are also born with a lighter belly color than adults. This form of cryptic coloration or camouflage is used to disguise the pup's appearance. A high mortality rate of the young pups is presumed, owing to the large litter size. The gestation period is unknown, but is probably more than two years, based on the gestation time of other hexanchiform sharks like the frilled sharks. Females reach sexual maturity at 4.5 m (15 ft) in length[4] and 18–35 years in age, while males reach sexual maturity much earlier at 3.15 m (10.3 ft) in size[1] and 11–14 years in age. Many biologists believe that the male bluntnose sixgill shark's teeth are specially adapted for courtship. The male nips at the female's gill slits using its longer-cusped teeth. This action is thought to entice the female into mating. Evidence of this hypothesis is that female bluntnose sixgill sharks show up with seasonal scars around their gill slits, which apparently is from breeding with males. Males and females are thought to meet seasonally between May and November.

Human interaction

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The bluntnose sixgill shark is sold for its meat and oil.[4]

The bluntnose sixgill shark is listed as Near Threatened by the International Union for Conservation of Nature (IUCN) because, despite its extensive range, its longevity and popularity as a sport fish makes it vulnerable to exploitation and unable to sustain targeted fishing for very long. Although population data is lacking in many areas for this species, certain regional populations have been classified as severely depleted. Although it is usually caught as bycatch, it is also caught for food and sport.[1] In June 2018, the New Zealand Department of Conservation classified the bluntnose sixgill shark as "Not Threatened" with the qualifiers "Data Poor" and "Secure Overseas" under the New Zealand Threat Classification System.[27]

Despite its massive size, this species is rather harmless to humans unless provoked.[4]

Recent research

Blue Planet II

Blue Planet II, a documentary on marine organisms produced by the BBC, featured an episode focussing on deep sea organisms and environments. In this episode, bluntnose sixgill sharks were filmed feeding on a whale fall. In behind-the-scenes footage, the sharks attacked the deep sea submersible as crew members tried to collect the video footage. Thinking that they were competition, the sharks used their bodies to try to fend off the submarine, only leaving it behind once they realized that the sub was not there to feed.[28] [1] The film crew was able to obtain useful video footage of the sixgills that they later featured in the episode. As a worldwide, well-known, scientific platform, it hence helped with the awareness of the existence of these species of sharks.

Tagging sixgills in their natural habitat

Since 2005, scientists have successfully been able to tag sixgill sharks as a means of studying their behavior. With this being said, however, as of 2019, there has yet to be a sixgill tagged in its natural deep-sea habitat. Researchers from Florida State University, the Florida Museum of Natural History, the Cape Eleuthera Institute, and OceanX hence decided to join forces to tag a deep-sea shark through use of a submersible, and they succeeded in doing so.[29] After 3 months of leaving the tag on the sixgill, the tag was thought to float up to the surface where scientists will be able to collect the data from that tag. Overall, this study showed how advancements in technology has helped scientists be better able to study marine life. Instead of having to go on an expedition for years at a time, the scientists here simply had to attach a tag onto the sixgill once and collect the data another time. The tag simply showed behavioral results of the sixgills.

References

  1. ^ a b c Finucci, B.; Barnett, A.; Bineesh, K.K.; Cheok, J.; Cotton, C.F.; Dharmadi, Graham, K.J.; Kulka, D.W.; Neat, F.C.; Pacoureau, N.; Rigby, C.L.; Tanaka, S.; Walker, T.I. (2020). "Hexanchus griseus". IUCN Red List of Threatened Species. 2020: e.T10030A495630. doi:10.2305/IUCN.UK.2020-3.RLTS.T10030A495630.en. Retrieved 19 November 2021.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ "Huge deep sea shark scavenges food". Newsweek. July 23, 2019.
  3. ^ Daly-Engel, Toby S.; Baremore, Ivy E.; Grubbs, R. Dean; Gulak, Simon J. B.; Graham, Rachel T.; Enzenauer, Michael P. (2019-04-01). "Resurrection of the sixgill shark Hexanchus vitulus Springer & Waller, 1969 (Hexanchiformes, Hexanchidae), with comments on its distribution in the northwest Atlantic Ocean". Marine Biodiversity. 49 (2): 759–768. doi:10.1007/s12526-018-0849-x. ISSN 1867-1624. S2CID 46764519.
  4. ^ a b c d e f g Tricas, Timothy C.; Deacon, Kevin; Last, Peter; McCosker, John E.; Walker, Terence I. (1997). Taylor, Leighton (ed.). The Nature Company Guides: Sharks & Rays. Sydney: Time-Life Books. pp. 138. ISBN 0-7835-4940-7.
  5. ^ McFarlane, Gordon A. and King, Jacquelynne R. and Saunders, Mark W. (2002) Preliminary study on the use of neural arches in the age determination of bluntnose sixgill sharks (Hexanchus griseus). Fishery Bulletin, 100(4), pp. 861-864. http://fishbull.noaa.gov/1004/17mcfarl.pdf
  6. ^ McClain, Craig R.; Balk, Meghan A.; Benfield, Mark C.; Branch, Trevor A.; Chen, Catherine; Cosgrove, James; Dove, Alistair D.M.; Gaskins, Leo C.; Helm, Rebecca R. (2015-01-13). "Sizing ocean giants: patterns of intraspecific size variation in marine megafauna". PeerJ. 3: e715. doi:10.7717/peerj.715. ISSN 2167-8359. PMC 4304853. PMID 25649000.
  7. ^ Lineaweaver, Thomas, & Richard H. Backus. (1969). The natural history of sharks. Lyons & Burford, New York, p. 169.
  8. ^ Capape, Christian; Hemida, Farid; Guélorget, Olivier; Barrull, Joan; Mate, Isabel; Ben Soussi, Jamila; Bradaï, Mohamed Nejmeddine (June 2004). "Reproductive biology of the Bluntnose sixgill shark Hexanchus griseus (Bonnaterre, 1788)(Chondrichthyes: Hexanchidae) from the Mediterranean Sea: a review". Acta Adriatica. Research Gate. 45 (1): 95–106. ISSN 0001-5113.
  9. ^ Ebert, David (1986). "Biological Aspects of the Sixgill Shark (Hexanchus griseus)". Research Gate.
  10. ^ Comfort, Christina M.; Weng, Kevin C. (May 2015). "Vertical habitat and behaviour of the bluntnose sixgill shark in Hawaii". Deep Sea Research Part II: Topical Studies in Oceanography. 115: 116–126. Bibcode:2015DSRII.115..116C. doi:10.1016/j.dsr2.2014.04.005.
  11. ^ a b c d Froese, Rainer; Pauly, Daniel (eds.) (2017). "Hexanchus griseus" in FishBase. 01 2017 version.
  12. ^ "Φωτογραφίες: Έπιασαν καρχαρία τεσσάρων μέτρων στον Αστακό Αιτωλοακαρνανίας" [4 meters Hexanchus griseus in Greece]. ProtoThema. 7 October 2017.
  13. ^ McFarlane, G. A.; King, J. R.; Saunders, M. W. (2002). "Preliminary study on the use of neural arches in the age determination of bluntnose sixgill sharks (Hexanchus griseus)" (PDF). Fishery Bulletin. 100: 861–864.
  14. ^ Bauml, Jessica. "Hexanchus griseus (Bluntnose Sixgill Shark)". Animal Diversity Web. Retrieved 2020-10-31.
  15. ^ Catoto, Roel (20 December 2017). "Rarely seen shark sighted in Ormoc Bay | MindaNews". www.mindanews.com. Retrieved 2017-12-22.
  16. ^ "'Look at the shark': Shark swims over oblivious divers in underwater video". USA TODAY.
  17. ^ "Scientists studying remains of pregnant sixgill shark found on Vancouver Island". The Globe and Mail. The Canadian Press. Retrieved 2019-02-07.
  18. ^ Coffey, Daniel M.; Royer, Mark A.; Meyer, Carl G.; Holland, Kim N. (2020-01-24). "Diel patterns in swimming behavior of a vertically migrating deepwater shark, the bluntnose sixgill (Hexanchus griseus)". PLOS ONE. 15 (1): e0228253. Bibcode:2020PLoSO..1528253C. doi:10.1371/journal.pone.0228253. ISSN 1932-6203. PMC 6980647. PMID 31978204.
  19. ^ Comfort, Christina M.; Weng, Kevin C. (2015-05-01). "Vertical habitat and behaviour of the bluntnose sixgill shark in Hawaii". Deep Sea Research Part II: Topical Studies in Oceanography. Biology of Deep-Water Chondrichthyans. 115: 116–126. Bibcode:2015DSRII.115..116C. doi:10.1016/j.dsr2.2014.04.005. ISSN 0967-0645.
  20. ^ Andrews, Kelly S.; Williams, Greg D.; Farrer, Debbie; Tolimieri, Nick; Harvey, Chris J.; Bargmann, Greg; Levin, Phillip S. (2009-08-01). "Diel activity patterns of sixgill sharks, Hexanchus griseus: the ups and downs of an apex predator". Animal Behaviour. 78 (2): 525–536. doi:10.1016/j.anbehav.2009.05.027. ISSN 0003-3472. S2CID 53161681.
  21. ^ Andrews, Kelly S.; Williams, Greg D.; Levin, Phillip S. (2010-09-08). Ropert-Coudert, Yan (ed.). "Seasonal and Ontogenetic Changes in Movement Patterns of Sixgill Sharks". PLOS ONE. 5 (9): e12549. Bibcode:2010PLoSO...512549A. doi:10.1371/journal.pone.0012549. ISSN 1932-6203. PMC 2935885. PMID 20838617.
  22. ^ McNeil, Bryan; Lowry, Dayv; Larson, Shawn; Griffing, Denise (2016-05-31). "Feeding Behavior of Subadult Sixgill Sharks (Hexanchus griseus) at a Bait Station". PLOS ONE. 11 (5): e0156730. Bibcode:2016PLoSO..1156730M. doi:10.1371/journal.pone.0156730. ISSN 1932-6203. PMC 4887027. PMID 27243237.
  23. ^ Reum, Jonathan C. P.; Williams, Gregory D.; Harvey, Chris J.; Andrews, Kelly S.; Levin, Phillip S. (February 2020). "Trophic ecology of a large-bodied marine predator, bluntnose sixgill shark Hexanchus griseus, inferred using stable isotope analysis". Environmental Biology of Fishes. 103 (2): 147–162. doi:10.1007/s10641-019-00941-z. ISSN 0378-1909. S2CID 209673396.
  24. ^ Ebert, David (1986). "Biological Aspects of the Sixgill Shark (Hexanchus griseus)". Research Gate.
  25. ^ Ebert, D. A. (June 1994). "Diet of the sixgill shark Hexanchus griseus off southern Africa". South African Journal of Marine Science. 14 (1): 213–218. doi:10.2989/025776194784287030. ISSN 0257-7615.
  26. ^ Nakamura, Itsumi; Meyer, Carl G.; Sato, Katsufumi (2015-06-10). Bailey, David Mark (ed.). "Unexpected Positive Buoyancy in Deep Sea Sharks, Hexanchus griseus, and a Echinorhinus cookei". PLOS ONE. 10 (6): e0127667. Bibcode:2015PLoSO..1027667N. doi:10.1371/journal.pone.0127667. ISSN 1932-6203. PMC 4489517. PMID 26061525.
  27. ^ Duffy, Clinton A. J.; Francis, Malcolm; Dunn, M. R.; Finucci, Brit; Ford, Richard; Hitchmough, Rod; Rolfe, Jeremy (2018). Conservation status of New Zealand chondrichthyans (chimaeras, sharks and rays), 2016 (PDF). Wellington, New Zealand: Department of Conservation. p. 10. ISBN 9781988514628. OCLC 1042901090.
  28. ^ "Blue Planet II behind the scenes: The moment giant sharks attack crew submarine - BBC News". YouTube. 2017.
  29. ^ Gilliland, Haley (2019). "Scientists Tag Deep-Sea Shark Hundreds of Feet Underwater—a First". National Geographic.

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Bluntnose sixgill shark: Brief Summary

provided by wikipedia EN

The bluntnose sixgill shark (Hexanchus griseus), often simply called the cow shark, is the largest hexanchoid shark, growing to 20 ft (6.1 m) in length. It is found in tropical and temperate waters worldwide and its diet is widely varied by region. The bluntnose sixgill is a species of sixgill sharks, of genus Hexanchus, a genus that also consists of two other species: the bigeye sixgill shark (Hexanchus nakamurai) and the Atlantic sixgill shark (Hexanchus vitulus). Through their base pairs of mitochondrial genes COI and ND2, these three species of sixgills widely differ from one another.

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Requin griset

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Hexanchus griseus

Le requin griset ou requin à maquereaux (Hexanchus griseus) est une espèce de requins de la famille des Hexanchidae.

À ne pas confondre avec le requin perlon qui est parfois également nommé « requin griset ».

Description

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Requin griset.

Le requin griset est un requin massif, possédant une large tête arrondie ou pointue. Il possède 6 paires de fentes branchiales et une seule nageoire dorsale à l'arrière du corps, caractères souvent décrits comme primitifs dans la littérature[1], ainsi que de petits yeux verts fluorescents et rétractables. La bouche est placée sur la face ventrale et contient 6 rangées de dents en forme de peigne. La queue est courte et trapue[2]. Il ne voit qu'en monochrome.

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Hexanchus griseus

Il mesure généralement entre 1,5 et 4,80 m de long[2], mais il peut parfois atteindre la taille impressionnante de 5 ou 6 m de long[3] pour un poids maximum mesuré de 590 kg[4]. Un spécimen d'environ 5 m a été observé au large de la Floride[5] le 29 juin 2019. Un spécimen de 8 m aurait été rapporté par la littérature mais il s'agirait vraisemblablement d'une erreur[6].

Hexanchus griseus se décline sur des tons gris à bruns foncés sur le dos, et présente un ventre gris argent[7],[3]. Sa cavité buccale est dotée de tâches foncées en une abondance spécifique à cette espèce[3].

Écologie et comportement

Alimentation

Le requin griset a un régime carnivore relativement généraliste[2],[3],[7]. Le contenu stomacal de spécimens péchés en mer Méditerranée[3] et en Afrique du sud[7] a révélé un régime alimentaire composé de poissons osseux[7],[2],[3] (mulet, merlu, sardine, etc.), des poissons cartilagineux (raies[2],[3] et petits requins[2],[7],[8]), ainsi que de divers crustacés[3] (homard et crabes), mollusques[3] (seiches et poulpes) et échinodermes. Il peut également se nourrir de mammifères marins (phocidés ou cétacés)[3],[7],[8]. Le régime alimentaire de Hexanchus griseus dépend de sa taille et de son habitat. Sur la plupart de ses aires de répartition, il est peu sujet à la compétition pour la recherche de nourriture puisqu'il est souvent le carnivore chassant les proies occupant les plus hauts niveaux trophiques[1]. Quelques espèces pouvant éventuellement entrer en compétition avec Hexanchus griseus sont recensées dans la littérature, en raison de leurs similarités avec le requin griset (taille, déplacements, etc.)[1]. Cependant les aires de chevauchement d'Hexanchus griseus restent limitées en raison de la diversité des biotopes qu'il exploite. Par ailleurs, il est possible que ces rivaux se contentent de proies plus petites en raison de la taille de leurs mâchoires[7],[1].

Reproduction

Le requin griset, à l'instar de nombreuses espèces de requin, est ovovivipare. La femelle donne naissance à des portées composées de nombreux petits (22 à 108)[2],[3],[6]. A la naissance, les petits mesurent une longueur totale comprise entre 60 et 75 cm[2],[8],[6]. Les femelles connaissent une croissance rapide et atteignent la maturité sexuelle quand leur taille dépasse 420 cm[8],[6] ce qui correspond à un âge de 18 à 35 ans[9], alors que des mâles ont été observés matures sexuellement à partir de 310 cm, c'est-à-dire entre 11 et 14 ans[8]. Les femelles arborent des marques de morsures après accouplement[3] et pratiquent la polyandrie. Une étude datant de 2011 portant sur l'analyse génétique de 71 embryons prélevés dans une femelle en gestation révèle la paternité d'au moins 9 individus mâles sur l'ensemble de la portée ainsi que l’existence de nombreux demi-frères et demi-sœurs au sein de l'échantillon de juvéniles capturés [10].

Habitat et répartition

Répartition

Le requin griset est l'un des requins les plus largement réparti au monde[10] puisqu'il est présent dans les mers tempérées ou tropicales de l'Atlantique Est et Ouest, du Pacifique Occidental, Central et Oriental, ainsi qu'en Mer Méditerranée[2],[3], bien que ses populations ne soient jamais très abondantes dans les zones d’observation[8].

Biotopes

Grâce à son régime alimentaire varié, Hexanchus griseus est capable d'exploiter une grande variété d'habitats. Il est réparti dans l'ensemble des océans du globe et dans de nombreux étages marins. Les lieux d'habitation du requin griset varient au cours de la vie et vraisemblablement en fonction du sexe de l'individu[7],[6]. Les juvéniles sont souvent observés près des côtes, sur les plateaux continentaux ou dans les eaux peu profondes des baies et des estuaires[7],[6]. Ils migrent peu au cours des premiers stades de leur vie et restent fidèles à leur lieu de naissance[10]. Les mâles ayant atteint une taille supérieure à 1,20m migrent vers des eaux plus profondes[7], entre -300 et -2 500 mètres[11], comme en atteste la modification de leur régime alimentaire dont témoignent les restes alimentaires des contenus stomacaux de spécimens étudiés[7]. Il est cependant possible d'en rencontrer dans des eaux de surface ([2],[3]. Les femelles vivent dans des eaux moins profondes[6].

Hexanchus griseus et l'homme

Le requin griset est inoffensif et ne représente pas de danger pour l'homme[3],[2]. Il lui arrive d'être pris par accident dans les filets de pêche. En raison de sa taille, il représente une source de nourriture importante mais peu valorisée[3]. Cependant, dans certaines régions de la Méditerranée, il représente un substitut aux stocks de poissons décroissants et fait l'objet d'une pêche plus importante[3]. Il est consommé, frais, séché, salé ou congelé, ou dans des préparations à base de poisson ainsi que sous forme d'huile[2]. Son attitude passive en fait un requin facile à pêcher à l'age adulte[2]. Contrairement à de nombreux requins dont les cycles de reproduction sont lents et les portées peu nombreuses, la descendance des requins grisets est abondante et contribue à maintenir les populations[3].

Voir aussi

Notes et références
  1. a b c et d (en) A. Barnett, J. M. Braccini, C. A. Awruch et D. A. Ebert, « An overview on the role of Hexanchiformes in marine ecosystems: biology, ecology and conservation status of a primitive order of modern sharks », Journal of Fish Biology, vol. 80, no 5,‎ avril 2012, p. 966–990 (DOI , lire en ligne, consulté le 2 août 2019)
  2. a b c d e f g h i j k l et m (en) Compagno, Leonard J. V., Sharks of the world : an annotated and illustrated catalogue of shark species known to date, United Nations Development Programme, 1984- (ISBN 92-5-101384-5, 9789251013847 et 9251013837, OCLC , lire en ligne), p. 19-20
  3. a b c d e f g h i j k l m n o p q et r (en) Antonio Celona, « BLUNTNOSE SIXGILL SHARK, HEXANCHUS GRISEUS (BONNATERRE, 1788), IN THE EASTERN NORTH SICILIAN WATERS », Boll. Mus. civ. St. nat.,‎ 2005, p. 15 (lire en ligne)
  4. Lamb, Andrew, 1947-, Coastal fishes of the Pacific Northwest, Harbour Pub, 1986 (ISBN 0-920080-75-8 et 9780920080757, OCLC , lire en ligne)
  5. https://la1ere.francetvinfo.fr/polynesie/images-epoustouflantes-requin-ere-prehistorique-732220.html
  6. a b c d e f et g Ebert, DA; Ocean Research Consulting Association, P.O. Box 281, Moss Landing, CA 95039, USA, Some observations on the reproductive biology of the sixgill shark Hexanchus griseus (Bonnaterre, 1788) from South African waters, NISC, 2002 (OCLC , lire en ligne), p. 359-363
  7. a b c d e f g h i j et k (en) D. A. Ebert, « Diet of the sixgill shark Hexanchus griseus off southern Africa », South African Journal of Marine Science, vol. 14, no 1,‎ juin 1994, p. 213–218 (ISSN , DOI , lire en ligne, consulté le 2 août 2019)
  8. a b c d e et f David A. Ebert, « Biological Aspects of the Sixgill Shark, Hexanchus griseus », Copeia, vol. 1986, no 1,‎ 10 février 1986, p. 131 (ISSN , DOI , lire en ligne, consulté le 2 août 2019)
  9. DUMAS Jacques, ADER Denis, MALIET Vincent, SITTLER Alain-Pierre, « Hexanchus griseus (Bonnaterre, 1788) », sur https://doris.ffessm.fr, Doris, 9 mai 2019 (consulté le 3 août 2019)
  10. a b et c (en) Shawn Larson, Jeff Christiansen, Denise Griffing et Jimiane Ashe, « Relatedness and polyandry of sixgill sharks, Hexanchus griseus, in an urban estuary », Conservation Genetics, vol. 12, no 3,‎ 1er juin 2011, p. 679–690 (ISSN , DOI , lire en ligne, consulté le 2 août 2019)
  11. Last, Peter R. (Peter Robert), Swainston, Roger, 1960-, Davis, Georgina. et CSIRO Publishing., Sharks and rays of Australia, CSIRO Publishing, 2009, 644 p. (ISBN 978-0-643-09457-4 et 0643094571, OCLC , lire en ligne)

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Requin griset: Brief Summary

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Hexanchus griseus

Le requin griset ou requin à maquereaux (Hexanchus griseus) est une espèce de requins de la famille des Hexanchidae.

À ne pas confondre avec le requin perlon qui est parfois également nommé « requin griset ».

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뭉툭코여섯줄아가미상어

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뭉툭코여섯줄아가미상어(Hexanchus griseus)는 신락상어과에 속하는 상어의 일종이다. 신락상어목 중에서 가장 큰 상어로 몸길이는 약 4.8m에 이른다.

특징

전 세계의 열대와 온대 해역에 널리 분포한다. 수심 2,000m까지의 심해에서 서식한다. 몸길이는 4.8m에 달한다. 등쪽 몸색깔은 회색이나 갈색 또는 올리브색을 띠고 있기도 한다. 배쪽으로는 흰색을 띤다. 등지느러미는 1개로 몸 뒷쪽에 위치하고 있다. 주둥이는 편평하고 크게 굽어 있다. 6쌍의 아가미 구멍을 갖고 있다. 상어는 대부분 5개의 아가미를 갖고 있는 데 반해, 6쌍의 아가미 구멍을 갖는 종은 큰눈여섯줄아가미상어(H. nakamurai)와 주름상어(Chlamydoselachus anguineus)가 있다. 치아 형태가 매우 특징적이며, 아랫턱 양쪽에 6개의 톱 모양의 이빨을 가지고 있다.

먹이의 종류는 풍부하여, 상어를 포함해 모든 어류, 갑각류, 두족류, 조개류, 포유류 등을 포식하다. 생식 방법은 태생이며, 자궁 내에서 알을 부화시키다. 한번에 22-108마리의 새끼를 낳는다. 출산 직후 새끼 상어의 크기는 약 60-75cm정도이다.

사람과의 관계

어업과 낚시의 대상이 된다. 수산물로는 고기와 간유(肝油, 상어기름)가 이용된다. 평소에는 심해에서 서식하기 때문에 사람과 부딪힐 확률이 낮기 때문에 두려워할 필요는 거의 없다. 그러나 강한 턱과 날카로운 이빨을 가지고 있기 때문에 낚시로 잡았을 때는 주의해야 한다.

각주

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Description

provided by World Register of Marine Species
Sits on the bottom by day, and rise to the surface at night to feed. Feeds on a wide range of marine organisms, including other sharks (conspecifics) rays, chimaeras, bony fishes including dolphinfishes, swordfish & marlin, herring, grenadiers, cod, ling, hake, flounders, gurnards & anglers, as well as squids, crabs, shrimps, carrion and even seals. Ovoviviparous with 22-108 in a litter. Not known to have attacked people without provocation. Sensitive to low light. Used for food either fresh, frozen, or dried salted. Also utilized for fishmeal and oil.
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Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (08/2021). Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (08/2021). Stocks, K. 2009. Seamounts Online: an online information system for seamount biology. Version 2009-1. World Wide Web electronic publication. North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS)
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Edward Vanden Berghe [email]
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Distribution

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Nova Scotia, in Emerald Basin, to Northern Argentina
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Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (08/2021). Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (08/2021). Stocks, K. 2009. Seamounts Online: an online information system for seamount biology. Version 2009-1. World Wide Web electronic publication. North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS)
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Kennedy, Mary [email]
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Kennedy, Mary [email]

Habitat

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nektonic
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Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (08/2021). Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (08/2021). Stocks, K. 2009. Seamounts Online: an online information system for seamount biology. Version 2009-1. World Wide Web electronic publication. North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS)
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Kennedy, Mary [email]
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Kennedy, Mary [email]

Habitat

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Known from seamounts and knolls
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Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (08/2021). Froese, R. & D. Pauly (Editors). (2021). FishBase. World Wide Web electronic publication. version (08/2021). Stocks, K. 2009. Seamounts Online: an online information system for seamount biology. Version 2009-1. World Wide Web electronic publication. North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS)
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[email]
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