Sharpnose sevengill shark

2/16/2016

Probably the most distinguishable part of the sharpnose sevengill shark, Heptranchias perlo, are its eyes. Placed on its narrow head, two big, fluorescent green eyes are what immediately stand out from this animal. And my, what pretty eyes they are…

The eyes aren’t the only captivating thing about this species. In family Hexanchidae, they are the only species in the Heptranchias genus.

This species is not to be confused with the broadnose sevengill shark (Notorynchus cepedianus). These sharks are the only extant member of the genus Notorynchus, in the family Hexanchidae. So, same family, similar name, very different sharks.

They are on the smaller spectrum when it comes to shark length, their max length being 1.4 m (4.6 ft). Although small, they are noted as voracious predators in their respective ecosystem. So, almost like dynamite- small, but they pack a punch. A dark grey/blue/brown color, they (like the broadnose sevengill shark) have one dorsal fin located behind their pelvic fins. Juveniles have dark blotches on the ventral side to begin with, fading to a creamy white with age. They have rather slim bodies, and unlike most sharks, have seven gills.

They are a pretty circumglobal animal, found in most tropical and temperate seas except the northeastern Pacific Ocean. This wide range suggested they are probably good swimmers. They are a deep-water shark, usually caught at around 300-600 m (980-1,970 ft) but have been seen on the surface (although this might be due to mis-identification).

They feed mainly at night, feasting upon small bony fish, shrimps, crabs, lobsters, squid, cuttlefish and even their cousins, rays. They do eat smaller sharks, and are also on the menu for larger sharks. These sharks suffer from parasites. Known parasites include nematodes in the genera Anisakis and Contracaecum, and the cestode, Crossobothrium dohrnii.

Reproduction is viviparous with yolk-sac, with no set "season" for reproduction being found yet. Gestation is unknown, however females are known to have 9-20 pups in each litter. Pups measure 0.25 m (0.8 ft) when born.

Very few sharpnose sevengill sharks are captured as bycatch by commercial fisheries on longlines or in trawls. They are primarily used for fishmeal and liver oil; although their meat is said to be good, it's said to be mildly poisonous to humans.

The IUCN has declared this species as Near Threatened (NT); scientists fear their unknown reproduction and and unknown population numbers can put this animal under pressure. These animals have been seen in captivity in Japan, though, so that's something cool to check out! There are currently no conservation actions in effect or proposed for this species.

did you know about this seven-gilled animal?

glossary

Bycatch: The part of a fishery’s catch that is made up of non-target species.
Circumglobal: Around the world; spanning the globe.
Commercial fishery: The activity of catching fish and other seafood for profit.
Dorsal fin: Fin located on the back.
Fluorescent: having or showing fluorescence.
Gestation: The period in which a fetus develops, beginning with fertilization and ends at birth.
IUCN: International Union for Conservation of Nature.
Pelvic fins: Fins located behind the gills on either side.
Pups: Baby sharks.
Viviparous with yolk-sac: Also known as aplacental viviparous and previously known as ovoviviparous/ovoviviparity; it is the production of eggs that are fertilised and hatch inside the female shark but the embryos lack a placental connection to the oviduct or uterus and so do not feed off the mother.