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