Broadnose sevengill shark
Large opportunistic and stealthy predator with 7 gills
The Broadnose Sevengill shark (Notorynchus cepedianus) is the only extant member of the genus Notorynchus, in the family Hexanchidae. It is recognizable because of its seven gill slits, while most shark species have five gill slits, except for the members of the order Hexanchiformes and the Sixgill sawshark.
Family: Hexanchidae – Cow Sharks
Common Name– Cow and Frilled Sharks
Common Name– Cow Sharks
Status: IUCN Red List DATA DEFICIENT
Average Size and Length: The length at birth is 15.5–17.5 inches. Mature male length is 4.9 feet and mature female length is around 7.2 feet. The maximum recorded length 9.8 feet.
Average Weight: The maximum recorded weight is 236 pounds.
Current Rare Mythical Sightings: The Broadnose Sevengill shark is also related to ancient sharks as fossils from the Jurassic Period (200 to 145 million years ago) also had seven gills.
Teeth and Jaw: It has a wide mouth with 6 rows of large has comb-shaped teeth. The top jaw has jagged cusped teeth. The tooth count is 15-16 in the upper jaw and 13 in the lower jaw.
Head: It has a large, broad head and small, blunt snout. The eyes are small.
Tail: The upper caudal fin is much longer than the lower one and is slightly notched near the tip.
Demographic, Distribution, Habitat, Environment and Range: The Broadnose Sevengill shark prefers cool, temperate, inshore waters. It has so far been found in the western Pacific Ocean off China, Japan, Australia, New Zealand, the eastern Pacific Ocean off Canada, United States and Chile, and the southern Atlantic Ocean off Argentina and South Africa. In San Francisco, California, it is significantly found in the San Francisco Bay particularly near the Golden Gate Bridge and Alcatraz Island. Large, old individuals tend to live in deep offshore environments as far down as 446 feet. However, most individuals live in either the deep channels of bays, or in the shallower waters of continental shelves and estuaries. These sharks are mainly benthic in nature, cruising along the sea floor and making an occasional venture to the surface. They often move inshore and offshore with rising and falling tides and out of low salinity conditions. They are most likely migratory.
Diet: The Broadnose Sevengill shark has been found to feed on sharks including Gummy shark, one of its main prey, and other Cow sharks, rays, chimaeras, cetaceans, pinnipeds, bony fishes and carrion. It will also feed on whatever it finds such as shark egg cases, sea snails and remains of rats and humans. Research in 2003 found that its diet consisted of 30% mammals with a frequency of occurrence of 35%.
These sharks occasionally hunt in packs to take down larger prey, using tactics such as stealth to succeed. After feeding, it slowly digests the food for several hours and days and can go weeks until eating again.
Large predatory sharks such as the Great White shark can be a threat and cannibalism among this shark has also been recorded.
Aesthetic Identification: The Broadnose Sevengill shark has a large, thick body. The dorsal surface is silver grey to brown above, and ventrally counter-shaded light below. The body and fins are covered in a scattering of small black & white spots. In juveniles, their fins often have white margins. Its single dorsal fin is set far back along the spine towards the caudal fin and is behind the pelvic fins.
Biology and Reproduction: The Broadnose Sevengill shark is ovoviviparous. Mating occurs between autumn and winter with the male maturing at 4 to 5 years and the female 11 to 21 years. The average reproductive age for a female is 20 to 25 years. After a 12-month gestation period, the female moves to a shallow bay or estuary to give birth between April and May to a large litter of between 82 and 95 pups, measuring 15.5–17.5 inches. Newborns double in length in 6 months. There is more than likely a 12-month recovery period for females after gestation.
The Broadnose Sevengill shark lives for between 30 and 50 years.
Research in 2010 found that this shark has very poorly calcified vertebrae that cannot be used for age and growth estimations.
Behavioral Traits, Sensing and Intelligence: The Broadnose Sevengill shark may use group formation to avoid predation. They have been studied and recorded to show equal amounts of activity during the day and night. However, they do prefer overcast conditions and turbid waters. They are more opportunistic than active, however can be active and strong.
The Broadnose Sevengill shark is social and have been found in aggregations. They are thought to be migratory, however different populations have different movements and patterns.
They are known to be powerful, top predators.
Speed: The Broadnose Sevengill shark is and active, strong swimmer. However, it hunts stealthily while making very little movement except for moving its caudal fin until dashing to strike.
Broadnose Sevengill Shark Future and Conservation: As recently as the 1930s and 1940s, the shark was targeted by fisheries along the coast of California and, once the commercial fishery receded, recreational fishing of the shark started in the 1980s and 1990s. The Broadnose Sevengill shark is listed as data deficient throughout most of its range, and as possibly Vulnerable in the northeast Pacific and Near Threatened in the eastern Pacific. It likely suffers great ongoing pressure from various types of fisheries, and from frequently being caught as bycatch. In Argentina, it’s fished by rod and reel and Broadnose Sevengill shark fishing competitions have been occurring since the 1960s. It is also threatened by water pollution and is hunted for its liver oil and hide which is considered good quality in places such as China. In the early 1980s, intense fishing in the San Francisco Bay caused a local decline. Its meat and fins are in demand in countries such as the USA, Brazil, Spain, Germany, Netherlands and Israel, and is packaged for frozen food. The Broadnose Sevengill is also a source of vitamin A and utilized by South African sport anglers for winter tournaments, however, this shark is not easy to land despite being readily hooked.
The Broadnose Sevengill shark is frequently kept in aquariums and can adapt in captivity.
Broadnose Sevengill Shark Recorded Attacks on Humans: It is considered potentially dangerous, but very few reports of unprovoked bites have been recorded worldwide.