BIGEYE SIXGILL SHARK|
Order - Hexanchiformes
Family - Hexanchidae
Genus - Hexanchus
Species - nakamurai
The bigeye sixgill shark was originally described as Hexanchus griseus nakamurai (Teng 1962) due to its close
relation to the bluntnose sixgill shark Hexanchus griseus. However, this name was later changed to the currently
valid name of Hexanchus nakamurai (Teng, 1962). The genus name Hexanchus is derived from the Greek "exa"
meaning six and "agcho" meaning narrow. The species name nakamurai honors Teng's colleague H. Nakamura. Hexanchus
vitulus Springer & Waller 1969 is a synonym used in previous scientific literature that refers to this species.
An interesting side note: Stewart Springer and Richard Waller described this shark from specimens caught in the
western North Atlantic Ocean, naming it Hexanchus vitulus. However, it appears they did not realize that
seven years previously, H. T. Teng described the same species in his doctoral dissertation. It is disputed whether
Teng's description is a formal publication. In 1991, it was concluded that the name H. nakamurai is a valid
name as copies of Teng's dissertation was widely distributed to Japanese ichthyologists when it was originally written.
This conclusion is now widely accepted, with revisions expected in upcoming publications.
The English language common name referring to this shark is bigeye sixgill shark in reference to its large
eyes and six gill slits. Other common names include cañabota ojigrande (Spanish), canhabota olho grande (Portuguese),
cazón de fondo (Spanish), griset (French), Grootoog-seskiefhaai (Afrikaans), grootoogzeskieuwshaai (Dutch), pating (Tagalog),
and requin-vache (French).
The bigeye sixgill shark is probably distributed worldwide in deep water. However it has been reported in the western
Atlantic Ocean from Mexico to the Bahamas, northern Cuba, Nicaragua, and Costa Rica. In the eastern Atlantic, this
shark is found from France south to Morocco, including the Mediterranean Sea. It may also reside off the coasts of
Côte d'Ivoire and Nigeria. In the Indian Ocean, this shark lives off the eastern and southern coasts of the African
continent and Aldabra Island (India). The distribution in the western Pacific Ocean includes Japan, Taiwan,
Philippines, New Caledonia, and Australia.
World distribution map for the bigeye sixgill shark
Although widely distributed, this shark has been reported in localized areas. Bigeye sixgill sharks are found on
continental and insular shelves at depths from 295-1,970 feet (90-600 m). As a primarily deepwater species, the bigeye
sixgill shark is usually found near the bottom substrate and may move toward the surface during the nighttime hours.
Importance to Humans
Bigeye sixgill shark head view: notice the large eyes
and six gill slits
© John Morrissey
- · Distinctive Features
This shark is small and relatively slender with a somewhat flattened, narrow pointed head and large eyes.
The mouth is ventrally located. There are six gill slits in contrast to the five gill slits that most
sharks possess. The single dorsal fin is small with the origin ranging from over the posterior half of
the base of pelvic fin to just behind the insertion point of the pelvic fin. The anal fin is smaller than
the dorsal fin and the caudal peduncle is long and slender.
The dorsal fin placement on the bigeye sixgill
© John Morrissey
Other species appearing similar to the bigeye sixgill shark include the bluntnose sixgill shark (Hexanchus griseus)
and the frill shark (Chlamydoselachus anguineus). The distinguishing feature of the much larger sixgill
shark is the six large teeth of either side of the lower jaw in contrast to the bigeye sixgill shark which only
has five teeth on each side of the lower jaw. The frill shark can be identified by a terminal rather than ventral
mouth and fang-like teeth.
- · Coloration
The dorsal surface of the bigeye sixgill shark is dark to light brownish gray, paling to a lighter underside. The
trailing edges of the fins have white margins. Live specimens have fluorescent green eyes. Juveniles have a black-tipped
upper caudal fin.
The ventrally located mouth contains nine teeth on each side of the upper jaw and 5 teeth on each side of the small
symphysial tooth in the lower jaw. The first two teeth in the upper jaw each have a narrow hooked cusp and lack cusplets.
The remaining teeth become wider and have more lateral cusplets toward the corners of the upper jaw. There is one small
symphysial tooth centrally located on the lower jaw. Each side of the lower jaw has five large teeth that are wide and
comb-like, each with a cusp and several large cusplets.
The bigeye sixgill shark may grow to a maximum of
5.6 feet in length
© John Morrissey
- ·Size, Age, and Growth
The maximum size of the bigeye sixgill shark is 5.9 feet (1.8 m) total length. The average size of this species is
5.6 feet (1.7 m) with weights around 44 pounds (20 kg). Males mature at 4.0-5.2 feet (1.2-1.6 m) in length and
females at 4.7-5.8 feet (142-178 cm).
- · Food Habits
Little is known regarding the feeding habits of this shark. Shark biologists believe that it probably feeds
on small to medium-sized bony fishes as well as a variety of bottom dwelling invertebrates. A small tuna was
found in one specimen's stomach contents, suggesting that the bigeye sixgill shark may feed at the surface.
- · Reproduction
The bigeye sixgill shark is ovoviviparous. Litter size may number up to 13, with each pup measuring approximately
17 inches (43 cm) at birth.
- · Predators
Large sharks are potential predators of the bigeye sixgill shark.
Of only slight importance to fisheries, the bigeye sixgill shark is caught on line gear and in trawls.
Danger to Humans
This shark is not considered dangerous to humans primarily due to its small size and deep water habitat.
According to the International Shark Attack File, there have not been any attacks attributed to this species.
The bigeye sixgill shark is currently not listed as threatened or vulnerable by the World Conservation Union (IUCN).
The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that
assesses the conservation status of species.