Heptranchias Perlo

– Sharpnose Sevengill Shark –

The sharpnose sevengill shark (Heptranchias perlo), also known as one-finned shark, perlon shark, sevengill cow shark, sharpsnouted sevengill or slender sevengill, is a species of shark in the family Hexanchidae, and the only living species in the genus Heptranchias.^[3] Found almost circumglobally in deep water, it is one of the few species of sharks with seven pairs of gill slits as opposed to the usual five. The other shark species with seven gill slits is the broadnose sevengill shark. Though small, this shark is an active, voracious predator of invertebrates and fish. When caught, this species is notably defensive and will attempt to bite. It is of minor commercial importance.^[4]

Description

This species has a slender, spindle-shaped body with a narrow pointed head. The eyes are very large and a fluorescent green in live specimens. The mouth is narrow and strongly curved, containing 9 – 11 teeth on both sides of the upper jaw and 5 teeth on both sides of the lower jaw. The upper teeth are narrow and hooked with small lateral cusps, while the lower teeth are wide and comb-shaped.

Unlike many other sharks, there are seven pairs of gill slits that extend towards the throat. There is a single small dorsal fin located behind the pelvic fins, with a straight front margin, a narrowly rounded tip, and a concave posterior margin. The pectoral fins are small with a faint convex outer margin. The anal fin is small with almost straight margins. The caudal peduncle is long, and the distance between the origin of the dorsal fin and the caudal fin is more than twice the base of the dorsal fin.

The closely overlapping dermal denticles are very thin and transparent; each is longer than wide, with a distinct median ridge and two lateral ridges ending in marginal teeth. The color varies from gray to olive green on the back and paler on the ventrally; some individuals have dark spots on the body or light hind fin margins. Juveniles have dark flank spots and dark spikes on the dorsal fin and upper caudal lobe.

Known parasites of the beef shark include nematodes of the genera Anisakis and Contracaecum, and the cestode Crossobothrium dohrnii.

Usually measuring 60–120 cm (2.0–3.9 ft) long, sharpnose sevengill sharks attain a maximum length of 1.4 m (4.6 ft). This species has a slender, fusiform body with a narrow, pointed head. The eyes are very large and fluoresce green in live specimens. The mouth is narrow and strongly curved, containing 9-11 teeth on either side of the upper jaw and five teeth on either side of the lower. The upper teeth are narrow and hook-shaped with small lateral cusps, while the lower teeth are broad and comb-shaped (except for a symmetrical symphysial tooth). Unlike most other sharks, there are seven pairs of gill slits that extend onto the throat.^[5][7]

A single small dorsal fin is located behind the pelvic fins, with a straight front margin, narrowly rounded tip, and concave rear margin. The pectoral fins are small with a weakly convex outer margin. The anal fin is small with nearly straight margins. The caudal peduncle is long, and the distance between the dorsal fin origin and the caudal fin is more than twice the dorsal fin base. The closely overlapping dermal denticles are very thin and transparent; each is longer than it is broad, bearing a distinct median ridge and two lateral ridges ending in marginal teeth. The coloration is brownish gray to olive above and lighter below; some individuals have dark blotches on the body or light posterior fin margins. Juveniles have dark blotches on the flank and dark tips on the dorsal fin and upper caudal lobe.^[4][5]

Distribution

The sharpnose sevengill shark is uncommon, but widely distributed in the tropical and temperate regions of all oceans except for the northeastern Pacific Ocean. It is found from North Carolina to Cuba, including the northern Gulf of Mexico, and from Venezuela to Argentina in the western Atlantic. In the eastern Atlantic, it occurs from Morocco to Namibia, including the Mediterranean Sea. It is reported from the Indian Ocean off southwestern India, Aldabra Island, southern Mozambique, and South Africa. In the Pacific Ocean, it is known from Japan to China, Indonesia, Australia, New Zealand, and northern Chile.^[5]

The beef shark is rare, but widespread in tropical and temperate regions of all oceans except the northeastern Pacific Ocean.

It is found from North Carolina to Cuba, including the northern Gulf of Mexico, and from Venezuela to Argentia in the western Atlantic. In the eastern Atlantic, it is found from Morocco to Namibia, including the Mediterranean Sea.

It has been sighted in the Indian Ocean off southwestern India, Aldabra Island, southern Mozambique and South Africa. In the Pacific Ocean, it is known from Japan to China, Indonesia, Australia, New Zealand and northern Chile.

Habitat

It is a demersal or semi-pelagic species usually captured at depths of 300 – 600m, but occasionally found close to the surface (although these reports may represent misidentification) or up to 1000m.

It is found primarily on the outer continental shelf and upper continental slope and may congregate around seamounts.

Taxonomy

The genus name Heptranchias is from the Greek heptra meaning “seven arms”,^{[clarification needed]} and agchein meaning “throttle”, referring to this shark’s seven pairs of gill slits. Other common names for this species include one-finned shark, perlon shark, sevengill cow shark, sevengilled Mediterranean shark, sevengilled shark, sharpnose seven-gill shark, snouted sevengill shark and slender sevengill shark.^[5] Some authors believe this species is distinct enough to merit its own family, Heptranchiidae.^[6]

Biology and Ecology

Alimentation

Despite its relatively modest size, the beef shark is considered a top predator of the ecosystem in which it lives.

At the Great Meteor Seamount in the eastern Atlantic, this species feeds mainly on teleosts and cephalopods, and to a lesser extent, on small cartilaginous fish.

Off the coast of Tunisia, crustaceans are the most hunted prey after teleosts.

Off Australia, this species consumes mostly teleosts, with the smaller individuals primarily feeding on mouse fish and the larger individuals feeding on snake mackerel and trichiuridae.

It is a strong swimmer, with power and activity levels especially at night.

This species may be preyed upon by larger sharks. Known parasites of the sharpnose sevengill shark include nematodes in the genera Anisakis and Contracaecum, and the cestode Crossobothrium dohrnii.^[5]

Dimensions

One of the largest specimens ever recorded in the Mediterranean is a 1m and 35cm female captured in the Adriatic in August 1926. Usually measuring 60cm – 1m and 20cm in length, beef sharks reach a maximum length of 1m and 40cm. .

Reproduction

Reproduction is ovoviviparous, with no apparent reproductive season. Females give birth to 9 – 20 young; newborns measure approximately 26cm in length. Males mature to 75 – 85cm in length and females to 90cm – 1m. The onset of sexual maturation in males can be marked by the formation of mucus on the tips of the pterygopods.

Relationship to Humans

The sharpnose sevengill shark is reasonably small and is located in generally deep water, and these characteristics classify this shark as harmless to humans.^[3] Small to moderate numbers of sharpnose sevengill sharks are captured as bycatch in certain deepwater commercial fisheries on longlines or in trawls.^[2] They are used for fishmeal and liver oil; the meat is said to be of good quality, but the flesh is considered to be mildly poisonous when consumed.^[5][7] When captured, it is very active and quick to bite, but it does not pose a substantial threat to people due to its small size.^[4] It has occasionally been kept in captivity in Japan.^[2]

Conservation Status

Some concern exists that populations of this slow-reproducing species may be declining in areas of sustained deepwater fishing, and it has been assessed as Near Threatened by the World Conservation Union.^[2] In June 2018 the New Zealand Department of Conservation classified the sharpnose sevengill shark as “At Risk – Naturally Uncommon” with the qualifiers “Data Poor” and “Secure Overseas” under the New Zealand Threat Classification System.^[9]

Curiosity

On 26 September 2019, in the morning, a dead carcass was found on Torre Pali’s beach, one small locality in Salento (Italy).

Dangers

This species can be preyed upon by large sharks. Small to moderate numbers of beef sharks are caught as bycatch from commercial deep-sea fishing with longlines or bottom trawls.

They are used for flour and liver oil; the meat is said to be of good quality but appears to be slightly toxic. When caught it is very active and ready to bite, but it does not pose a considerable threat to humans due to its small size.

There is some concern that populations of this slow-breeding species may be declining in sustained deep-sea fishing areas, and it has been rated Nearly Endangered by the World Conservation Union. It was occasionally kept in captivity in Japan.

Further Information

The beef shark is a species of shark in the Hexanchidae family, and the only species in the genus Heptranchias. Found in the depths of almost all over the world, it is one of the few shark species with seven pairs of gill slits compared to the usual five.

Although small, this shark is an active and voracious predator of invertebrates and fish. If caught, this species is remarkably aggressive and will try to bite. It is of little commercial importance. The genus name Heptranchias comes from the Greek heptra meaning “seven arms”, and agchein means “valve”, referring to the seven pairs of gill slits of this shark. Other common names for this species are a single fin shark, seven gill cow shark, seven gill Mediterranean shark, seven gill shark, pointed nose seven gill shark, and slender seven gill shark.

Some authors believe that this species stands out enough to deserve its family, Heptranchiidae.