Sevengill Sharks, Notorynchus cepedianus
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Description & Behavior
Sevengill sharks, Notorynchus cepedianus (Péron, 1807), aka bluntnoses, broadnoses, broad snouted, broad-snouts, broadsnout sevengill sharks, Pacific seven-gills, and Tasmanian tiger sharks, are members of the most ancient frill and cow sharks order, Hexanchiformes. Hexanchiform sharks are identified by a single dorsal fin set far back on their bodies, either six or seven gill slits (versus the five found in all other existing sharks), and no nictitating membranes (protective third eyelids). Frilled sharks, Chlamydoselachus sp., are so different from the cow sharks that they are likely to be moved to their own Order Chlamydoselachiformes in the near future.
There are currently four known species of cow sharks:
- Sevengill sharks, Notorynchus cepedianus,
- Sharpnose sevengill sharks, Heptranchias perlo,
- Sixgill sharks, Hexanchus griseus, and
- Bigeyed sixgill sharks, Hexanchus nakamurai.
Sevengill sharks, named for having seven gill slits on either side of their bodies, reach lengths of at least 3 m with an average length of 1.5 m. They weigh up to 107 kg and are known to live as long as 49 years. Sevengills are thought to reach sexual maturity when they reach 1.5 to 2.2 m in length.
These are large active sharks with wide heads, small eyes, short blunt snouts and fusiform (spindle-shaped, wide in the middle, tapering at both ends) bodies. They have small single dorsal fins that are set far back over their pelvic fins. Their anal fin is smaller than their dorsal fin.
Sevengill sharks have a tooth "count" of 15-16/13 (upper/lower jaw). Their teeth are wide, large and comb-shaped in their lower jaws, which they use to tear and cut into prey. The teeth in their upper jaws are sharp and jagged which they use to hold onto prey.
Sevengill sharks are reddish-brown to silvery-gray or olive-brown with numerous small black spots on their bodies and fins; their undersides are a light or cream color. This counter-shading is a common type of camouflage that helps the sevengill blend into the sea bottom or ocean depths when viewed from above and the lighter surface waters when viewed from below. This counter-shading is also common among many pelagic species of sharks and fishes as well as other marine species.
Sharpnose sevengill sharks, Heptranchias perlo is a similar species but can be distinguished by the lack of black spots on the body as well as larger eyes and smaller bodies than sevengills.
World Range & Habitat
Sevengill sharks, Notorynchus cepedianus, are demersal (on or near the bottom of the sea) and at depths of 0 - 570 m with a typical depth of around 80 m. They inhabit waters of the subtropics at 56°N - 55°S, 131°W - 177°E. Sevengills are usually found over the continental shelves and often in shallow waters. They are often sighted close inshore, in bays and estuaries, with larger individuals having ranges that include deeper waters offshore and deep channels in bays to 570 m. They are seen usually cruising slowly near the bottom, even in waters as shallow as a meter, and sometimes at the surface. Sevengills are known to attack at great speeds when pursuing prey. These sharks seem to prefer rocky bottom habitats although they commonly occur over sandy and muddy bottoms as well.
Sevengills are circumglobal (distributed around the world within a range of latitudes) in tropical to temperate waters except for the North Atlantic and Mediterranean Sea. Sevengills are found in the southwest Atlantic in the waters off southern Brazil to northern Argentina. They are also found in the southeast Atlantic off Namibia to East London, South Africa. In the western Pacific, they are found off southern Japan to New Zealand and in the eastern Pacific, they are found from British Columbia, Canada to Chile.
Feeding Behavior (Ecology)
Sevengill sharks, Notorynchus cepedianus, typically feed on relatively large fish of all kinds, including other sharks, as well as crustaceans and carrion. They are opportunistic predators and have been found to eat almost anything including rays, chimaeras, hagfish, dolphins, porpoises, seals, shark egg cases, sea snails and rats and human carrion (dead bodies found at sea).
Sevengill sharks sometimes hunt in packs, working as a team to capture large prey such as marine mammals and other sharks. They are also known to stalk prey from behind and then swim forward rapidly to capture prey.
Sevengill sharks, Notorynchus cepedianus, like all cow sharks, are ovoviviparous, with the embryos developing inside eggs-cases inside the mother's body until they hatch, with 82 to 95 pups per litter.
Female sevengills are known to move into shallow bays to give birth, after a 12 month gestation period, during the spring and early summer. Each pup measures about 40-45 cm in length. Young sevengills remain in shallow water nursery grounds before moving out to deeper offshore environments in the first few years of their lives.
Conservation Status & Comments
Sevengill sharks, Notorynchus cepedianus, are currently listed as Data deficient (DD) on the IUCN Red List: "This assessment is based on the information published in the 2005 shark status survey (Fowler et al. 2005).
Although wide ranging and moderately common (where not heavily exploited), the Broadnose Sevengill Shark (Notorynchus cepedianus) is restricted to a limited inshore depth range in heavily fished temperate waters and is exposed to intensive inshore fisheries over most of its range. The central Californian stock in the San Francisco Bay area is thought to have been depleted in the early 1980s, but lack of fisheries data elsewhere make it impossible to determine whether this pattern of depletion definitely operates throughout its range."
Major threats to sevengills, according to IUCN: "This shark's flesh is of good quality and it is also taken in some areas for its hide and liver oil. Intensive commercial and sports fisheries in San Francisco Bay targeting it for its fine meat caused a marked local decline in numbers during the early 1980s. It is utilised in China for its skin and liver. Pollution may be a possible threat to inshore bays which are nurseries.
Although wide ranging in temperate waters and moderately common where not heavily exploited (e.g., southern Africa), this large shark has a limited inshore bathymetric range in heavily fished temperate waters and is often concentrated in shallow bays. This exposes it to intensive inshore bycatch and sometimes targeted commercial, sports and semi-commercial fisheries over most of its range, particularly off China, California, Argentina, Namibia and South Africa (Compagno in prep. a). Catch statistics are not reported, except for the west coast of the USA, which show a peak in landings of 1.55 t in 1981 with a sharp decline to less than 0.1 t in 1986 (Compagno in prep. a)."
According to the FLMNH Ichthyology Department (home of the International Shark Attack File): "During the 1930s and 1940s, the sevengill shark was quite common in the shark fisheries along the coast of California. Although the commercial fishery soon collapsed, recreational shark fishing for this species became popular. However, this fishery declined in the late 1980s and 1990s with recreational fishers targeting other species. Today the sevengill shark is caught primarily by anglers as well as incidental bycatch in commercial fisheries targeting other species.
Currently, the California population of sevengill sharks appears to be concentrated in the Humboldt and San Francisco Bays. These two areas provide nursery areas and safe havens for juveniles. The future of the sevengill shark in this region is highly dependent upon the conservation of these habitats.
Although this shark has a wide range, it is subject to intense fishing pressure as a result of being restricted to inshore waters. Currently the World Conservation Union (IUCN) lists the sevengill shark as "Data Deficient". Data is lacking in most regions, making it difficult to determine the overall status of this species. However, it is currently assessed as "Near Threatened" in the eastern Pacific Ocean."
Conservation Actions: There is generally no management of fisheries or protection for this species, although it occurs in at least one marine reserve in South Africa.
Sevengills are often caught by anglers from the shore and are consumed by humans, their skin for leather and their liver as a source of oil. They are commercially and recreationally fished for throughout their range in the eastern Pacific Ocean, from British Columbia to southern California, as well as in Australian waters. Sevengills are also often taken as incidental bycatch in the driftnet and trawl fisheries off the coast of California.
Sevengills are known to be aggressive when provoked and are regarded as potentially dangerous to people in open waters. They have attacked divers in captivity and may have been involved in a few shark attacks off California and South Africa. According to the International Shark Attack File, the sevengill shark has been responsible for five documented unprovoked attacks on humans since the 16th century.
References & Further Research
The Sevengill Shark (Notorynchus cepedianus) facebook group
Are Sevengill Sharks Making a Comeback? - tracking sevengill shark encounters in the San Diego area
Elasmodiver.com - image database of sharks, skates, rays, and chimaera's from around the world by Andy Murch
Shark Observation Network: collection of obsevation data and the development and dissemination of information concerning the state of shark and elasmobranch populations worldwide.
Research Notorynchus cepedianus » 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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