Animal Diversity Web

Ge­o­graphic Range

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. (Mac­Quity and King, 2000)

• Biogeographic Regions
• indian ocean
• atlantic ocean
• pacific ocean
• mediterranean sea

• Other Geographic Terms
• cosmopolitan

Habi­tat

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. (Mar­tin, 2000; Mu­sick and McMil­lan, 2002)

• Habitat Regions
• temperate
• tropical
• saltwater or marine

• Aquatic Biomes
• benthic
• coastal

• Range depth

  3 to 2,500 m

  9.84 to ft

Phys­i­cal De­scrip­tion

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. (Mac­Quity and King, 2000; Mar­tin, 2000)

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. (Parker and Parker, 2002)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• female larger

• Range mass

  480 to 720 kg

  1057.27 to 1585.90 lb

• Average mass

  500 kg

  1101.32 lb

• Range length

  3.5 to 4.8 m

  11.48 to 15.75 ft

• Average length

  3.7 m

  12.14 ft

De­vel­op­ment

Lit­tle is yet known about the life cycle and fetal de­vel­op­ment of Hexa­nchus griseus. (Ebert, 2002)

Re­pro­duc­tion

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. (Mac­Quity and King, 2000)

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. (Mu­sick and McMil­lan, 2002; Parker and Parker, 2002)

• Key Reproductive Features
• seasonal breeding
• sexual
• fertilization
  • internal
• ovoviviparous

• 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

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. (Mar­tin, 2000)

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifes­pan/Longevity

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. (Mc­Far­lane , et al., 2002; Mu­sick and McMil­lan, 2002)

• Average lifespan
  Status: wild

  about 80 years

Be­hav­ior

Re­searchers have had very lit­tle op­por­tu­nity to ob­serve the blunt­nose sixgill shark's be­hav­ior in the wild. These sharks are mainly soli­tary an­i­mals and most likely never swim in schools or seek out in­ter­ac­tion. Some re­searchers, how­ever, have spec­u­lated that H. griseus re­turn to shal­low wa­ters year after year (dur­ing the months of May to No­vem­ber) in order to in­ter­act so­cially with other blunt­nose sharks, most likely for the sole pur­pose of mat­ing. Richard Mar­tin sug­gests that these light-sen­si­tive sharks are drawn up to the shal­lower depths due to the yearly sum­mer algae bloom which greatly in­creases light at­ten­u­a­tion, al­low­ing the sharks com­fort while pro­vid­ing them with more prey items. Dur­ing these sea­sonal in­ter­ac­tions, males are be­lieved to nip at the gills of fe­males to court the fe­males. Dur­ing non-mat­ing sea­son, H. griseus re­mains at the lower depths ris­ing only to feed at night. (Mar­tin, 2000; Parker and Parker, 2002)

• Key Behaviors
• natatorial
• nocturnal
• motile
• migratory
• solitary

Com­mu­ni­ca­tion and Per­cep­tion

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). (Mac­Quity and King, 2000; Mu­sick and McMil­lan, 2002)

• Communication Channels
• visual
• tactile

• Perception Channels
• visual
• tactile
• acoustic
• vibrations
• chemical
• electric

Food Habits

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. (Parker and Parker, 2002)

• Primary Diet
• carnivore
  • piscivore
  • eats non-insect arthropods
  • molluscivore

• Animal Foods
• mammals
• fish
• carrion
• mollusks
• aquatic crustaceans

Pre­da­tion

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. (Mar­tin, 2000; Mar­tin, 2000)

• Known Predators

  • Steller's sea lions (Eumetopias jubatus)
  • great white sharks (Carcharodon carcharias)
  • killer whales (Orcinus orca)

Ecosys­tem Roles

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. (Mar­tin, 2000; Mu­sick and McMil­lan, 2002)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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. (Bester, 2001; Mac­Quity and King, 2000; Mar­tin, 2000; Mc­Far­lane , et al., 2002)

• Positive Impacts
• food

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

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.

Con­ser­va­tion Sta­tus

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. (Bester, 2001)

• IUCN Red List

  Near Threatened
  More information

• IUCN Red List

  Near Threatened
  More information

• US Federal List

  No special status

• CITES

  No special status

Other Com­ments

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.

Con­trib­u­tors

David Ar­mitage (ed­i­tor), An­i­mal Di­ver­sity Web, George Ham­mond (ed­i­tor), An­i­mal Di­ver­sity Web.

Jes­sica Bauml (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Phil Myers (ed­i­tor), Mu­seum of Zo­ol­ogy, Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

Shark Foun­da­tion. "Hexa­nchus griseus" (On-line ). Ac­cessed 3/17/03 at http://​www.​shark.​ch/​cgi-bin/​Sharks/​spec_​conv.​pl?​E+Hexanchus.​griseus.

IUCN. "IUCN Red List of Threat­ened Species: Hexa­nchus griseus" (On-line ). Ac­cessed 3/19/03 at http://​www.​redlist.​org/​search/​details.​php?​species=10030.

Bester, C. 2001. "Blunt­nose Sixgill Shark" (On-line). Ic­thy­ol­ogy at the Florida Mu­seum of Nat­ural His­tory. Ac­cessed De­cem­ber 07, 2004 at http://​www.​flmnh.​ufl.​edu/​fish/​Gallery/​Descript/​BSixgill/​Bsixgill.​html.

Ebert, D. 2002. Some ob­ser­va­tions on the re­pro­duc­tive bi­ol­ogy of the Sixgill Shark Hexa­nchus griseus . South African Jour­nal of Ma­rine Sci­ence, 24: 359-363.

Mac­Quity, M., D. King. 2000. SHARKS. New York: DK Pub­lish­ing, Inc.

Mar­tin, R. 2000. "Bi­ol­ogy of the Blunt­nose Sixgill" (On-line). Ac­cessed July 28, 2004 at http://​elasmo-research.​org/​research/​sixgill.​htm.

Mc­Far­lane , G., J. King, M. Saun­ders . 2002. Pre­lim­i­nary study on the use of neural arches in the age de­ter­mi­na­tion of blunt­nose sixgill sharks. Fish Bul­letin, 4: 861-864.

Mu­sick, J. A., B. McMil­lan. 2002. The Shark Chron­i­cles. New York: Henry Holt and Com­pany, Inc.

Nev­ell, L. "British Ma­rine Life Study So­ci­ety: Six-gilled Shark" (On-line ). Ac­cessed 3/17/03 at http://​ourworld.​compuserve.​com/​homepages/​BMLSS/​six-gill.​htm.

Parker, S., J. Parker. 2002. The En­cy­clo­pe­dia of Sharks. On­tario: Fire­fly Books LTD.