Broadnose Sevengill Shark, Notoryncus cepedianus
Broadnose Sevengill Shark, Notoryncus cepedianus. Fish caught from coastal waters off San Diego, California, March 2018. Length: 1.96 m (6 feet 4 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.
Broadnose Sevengill Shark, Notoryncus cepedianus. Fish caught from coastal waters off San Diego, California, March 2018. Length: 2.06 m (6 feet 9 inches). Catch, photograph and identification courtesy of Ben Cantrell, San Diego, California.
The Broadnose Sevengill Shark, Notoryncus cepedianus, is a member of the Cow Shark or Hexanchidae Family, also known as the Cow Shark, the Mud Shark, the Sevengill Shark and the Sevengill and in Mexico as tiburón de siete banquias and tiburón pinto. This fish is the sole member of the genus Notoryncus, and it is found in Mexican waters of the Pacific Ocean.
The Broadnose Sevengill Shark has a heavy large thick fusiform body. They are reddish-brown to silvery gray or olive color dorsally, transitioning to pale white ventrally. Their fins and body are covered with numerous small black and white spots. In juveniles the margins of the fins are white and they have a black stripe from the caudal peduncle to the tip of the caudal fin. The Broadnose Sevengill has a broadly rounded head, a broad blunt snout, a short blunt nose, small eyes, and a wide mouth located ventrally, equipped with 15 or 16 jagged cusped teeth on the top jaw and 13 comb-shaped teeth on the bottom jaw, and seven gill slits that are found in front of the pectoral fins, giving rise to their common name. Their anal fin is smaller than their single small dorsal fin which is set far back on the body just behind their pelvic fins; and, their caudal fin has a much larger upper lobe than lower lobe and has a slight notch near the tip.
The Broadnose Sevengill Shark is highly migratory. They are primarily a deepwater species that resides on the outer continental shelf and insular shelves over rocky bottom habitats and inshore over sandy and muddy bottoms. They are found from the surface to depths up to 570 m (1,870 feet) and are normally found swimming slowly just above the ocean floor. They associate in groups with other individuals of the same sex and size. Their movements in bays are correlated with tides. They are found in waters with temperatures between 12oC (54oF) and 18oC (65oF) at depths up to 570 m (1,870 feet). They are sexually dimorphic with females being larger than males and the males sexually maturing sooner than females. They reach a maximum of 2.96 m (9 feet 9 inches) in length and 182 kg (400 pounds) in weight. As of January 1, 2023, the International Game Fish Association world record stood at 155 kg (342 lbs) with the fish caught in San Francisco Bay, San Francisco, California, July 2017. They are a diurnal species, inactive and resting on the bottom during daylight hours and migrating vertically toward the surface and shallow waters to feed at night. They will occasionally spy-hop, sticking their head above the water. They are opportunistic predators that that are known to hunt in packs. They feed on a wide variety of bony fishes including chimaeras, rays, sharks and marine mammals such as dolphins, porpoises, and seals. In shallow water environments they are the top end predator that hunts as lie-in-wait stealth ambush predators known for making lightening attacks. The juveniles consume bivalves, cephalopods and crustaceans. They have low metabolic rates and only require one-tenth of their body weight for food on a monthly basis and can go for days without eating. Reproduction is ovoviviparous and polygynandrous (promiscuous) and involves a 2-year cycle (biennial), internal fertilization, a 12-month gestation period. The eggs hatch inside the female’s body and the embryos receive nourishment via a yolk sac inside the uterus. When the yolk sac is depleted, the embryos absorb nutrients from secretions within the uterus until they are born. Litter sizes are 82 to 95, miniature adult-like pups that are 40 cm (15.5 inches) and 45 cm (17.5 inches) in length. They are released in shallow bay and estuary environments and are on their own, having to fend for themselves. As they mature, they move into deeper waters. They have well-developed chemical sensory abilities, as well as being able to detect changes in water pressure and electrical currents. They have lifespans of up to fifty years.
The Broadnose Sevengill Shark has few known predators. They are known to be preyed upon by the Great White Shark, Carcharodon carcharias, and Killer Whales, Orcinus orca. They are also known to practice cannibalism.
The Broadnose Sevengill Shark is a wide-ranging circumglobal species, however they are absent from the north Atlantic and the Mediterranean. In Mexico they are a resident of the Pacific Ocean but have a limited distribution being found only along the entire west coast of Baja.
The Broadnose Sevengill Shark is a straightforward identification due to their body profile, color and gill ray counts. They are similar to the Bluntnose Sixgill Shark, Hexanchus griseus (six gills) and the Swell Shark, Cephaloscyllium ventriosum (darks bars and spots on the body). They are also similar to the Sharpnose Sevengill Shark, Heptranchias perlo (in Mexican waters an Atlantic Ocean only species; larger eyes, pointed snout; lack spots on the dorsal surface).
From a conservation perspective the Sevengill Shark is currently considered to be Data Deficient as their catch levels are poorly reported and poorly documented. In some parts of their range, specially the Eastern Tropical Pacific, their populations have declined significantly and they are considered to be Near Threatened. In some parts of their region they are utilized for human food and processed for their leather, liver oil and vitamin A. In some regions that are fished commercially, they are also caught with some frequency as a by-catch in drift nets and trawls. They are also pursued heavily by recreational anglers including shore anglers as they are easily hooked, but exceeding difficult to land. The Sevengill Shark is aggressive when provoked and is considered potentially dangerous to humans. Only five documented unprovoked attacks on humans have occurred since the 16th century with no known fatalities. They can be found in large public aquariums since they quickly adapt to captivity. Historically they were heavily pursued in California by commercial fishermen; in the 1940s this fishery receded. In the late 1980s the Broadnose Sevengill became popular with the recreational fishermen. They are decedents of seven gills that date to the Early Cretaceous Period (145,000,000 years ago).