Sharpnose Sevengill Sharks, Heptranchias perlo
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Description & Behavior
Sharpnose sevengill sharks, Heptranchias perlo (Bonnaterre, 1788), aka one-finned sharks, perlon sharks, sevengill cow sharks, sevengilled Mediterranean sharks, sevengilled sharks, sharpnose seven-gill sharks, snouted sevengill sharks and slender sevengill sharks, are members of the most ancient frill and cow sharks order, Hexanchiformes. Hexanchiform sharks have a single dorsal fin, either six or seven gill slits (versus the 5 found in all other existing sharks), and no nictitating membranes (protective third eyelids).
There are currently four known species of cow shark:
- Sharpnose sevengill sharks, Heptranchias perlo,
- Sevengill sharks, Notorynchus cepedianus,
- Sixgill sharks, Hexanchus griseus, and
- Bigeyed sixgill sharks, Hexanchus nakamurai.
Sharpnose sevengills are deepwater sharks and the smallest of the cow sharks, reaching lengths up to only 1.37 m for males and 1.4 m for females. They are commonly 1 m in length though an unconfirmed record exists of a sharpnose sevengill that was 2.14 m. They are believed to reach sexual maturity when they reach lengths of between 0.75 and 0.98 m.
Sharpnose sevegills have narrow heads with long narrow mouths (hence the name "sharpnose"), seven gill slit pairs, slender fusiform (spindle-shaped) bodies, and small dorsal fins set far back over their pelvic fins. Sharpnose sevengills are brownish gray above and lighter below, sometimes with indistinct dark blotches, and juveniles have dark-tipped dorsal and caudal fins while adults tend to have light fin margins. Sharpnose sevengills have beautiful fluorescent green eyes.
Sharpnose sevengill sharks may be confused with broadnose sevengill sharks, Notorynchus cepedianus, though broadnoses are usually much larger, have smaller eyes, broad, rounded snouts and the distinctive black spots covering their bodies.
Sharpnose sevengills' first 3 or 4 teeth in their upper jaws are narrow with hook-like cusps and small lateral cusps while their other teeth have one or two small cusps. Their teeth in the lower jaws are broad and comb-shaped with the exception of a small symmetrical tooth located at the symphysis (joint where the sides of the jaws meet). There are 9-11 teeth on each side of the upper jaw and 5 teeth on each side of the symphysial tooth on the lower jaw (see photos here).
World Range & Habitat
Sharpnose sevengill sharks, Heptranchias perlo, are a deepwater bathydemersal (living and feeding on the bottom below 200 m) species and are found in waters usually over outer continental and island (insular) shelves at depths from 0 to 1,000 m on or near the bottom.
Sharpnose sevengills are circumglobal (58°N - 58°S, 98°W - 173°W) in tropical and temperate seas, except for the northeast Pacific. They are found in the western Atlantic from North Carolina, USA and northern Gulf of Mexico south to Cuba and from Venezuela to Argentina. They are also in the eastern Atlantic off Morocco south to Namibia, including the Mediterranean Sea. They have also been found in the Indian Ocean from southwestern India, Aldabra Island, to southern Mozambique and South Africa. In the western Pacific, sharpnose sevengills are found from Japan to China and south to Indonesia, Australia and New Zealand. In the southeast Pacific, they have been found off northern Chile.
Feeding Behavior (Ecology)
Sharpnose sevengill sharks, Heptranchias perlo, are voracious deepwater predators that feed mostly at night on smaller sharks and rays, small bony fish, shrimps, crabs, lobsters, squid, and cuttlefish. Larger sharks are likely predators of sharpnose sevengill sharks.
Sharpnose sevengill sharks, Heptranchias perlo, reproduce by ovoviviparity with 9-12 young born per litter in what appears to be no set reproductive season. Newborn pups measure about 0.25 m in length.
Conservation Status & Comments
Sharpnose sevengill sharks, Heptranchias perlo, are listed as Near Threatened (NT) on the IUCN Red List: "A wide ranging, but relatively uncommon species where it occurs. Its centers of abundance may be at outer shelf, slope, and oceanic seamounts where commercial fisheries for other target species are likely to develop. It is likely to have a low intrinsic rate of increase, and poor resilience to depletion. This species is of minor commercial importance, but bycatch in bottom trawl and longline fisheries may have caused population declines where deepwater fisheries have been underway for several decades. Increased deepwater fishing effort in many regions is likely to affect populations in the future. The species is assessed as Near Threatened due to concern that it may meet the Vulnerable A2d+A3d+4d criteria."
Sharpnose sevengills are considered harmless to humans, however, they are very active and aggressive when captured and are quick to bite. Their liver is utilized as a source of oil though they are poisonous to eat.
Although of only minor commercial fishery interest, the sharpnose sevengill shark is caught primarily as bycatch in fisheries using bottom trawls and longlines which may cause future declines of populations of this slow-reproducing species.
There are currently no conservation actions in effect or proposed for this species.
References & Further Research
The Sevengill Shark (Notorynchus cepedianus) facebook group
Shark Observation Network: collection of obsevation data and the development and dissemination of information concerning the state of shark and elasmobranch populations worldwide.
ARKive - Sharpnose sevengill shark videos, photos and facts - Heptranchias perlo
Research Heptranchias perlo » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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