This week’s Featured Species focuses on one of the more primitive shark forms, first appearing in the fossil record around 100 to 60 million years ago, around the dawn of the age of modern sharks (Klimley, 2013). The Broadnose Sevengill Shark (Notorynchus cepedianus) belongs to the Hexanchidae family, which is made up of the five species of six and seven gilled cow sharks:
- Bluntnose Sixgill Shark (Hexanchus griseus)
- Bigeyed Sixgill Shark (Hexanchus nakamurai)
- Sharpnose Sevengill Shark (Heptranchias perlo)
- Broadnose Sevengill Shark (Notorynchus cepedianus)
- And the recently discovered Atlantic sixgill (Hexanchus vitulus)
The cow sharks are generally characterized by a single dorsal fin set low on the back near the caudal fin (Tricas, et al., 1997). These sharks are also known and named for their extra pair or pairs of gills – in the case of the sevengill cow sharks (Skomal, 2016). With the exception of the cow sharks’ immediate cousins, the Frilled Sharks (members of family Chlamydoselachidae, which are the only other members, beside Hexanchidae, of the order Hexanchiformes), all other species of shark have five pairs of gill slits. The sixgilled sharks are the larger species in the family, reaching lengths of nearly 16 feet (4.8 m), while the smaller sevengilled sharks reach lengths of 10 feet (5.04 m) (Tricas, et al., 1997).
The broadnose sevengill sharks may also resemble their prehistoric ancestors in their internal body structures. Extant sharks – that is sharks that are alive today – exhibit two major brain organization patterns:
- Primitive – This form is found in the six and sevengill sharks, sawsharks, angelsharks, and dogfishes (these sharks are sometimes referred to as Squaloforms). These sharks exhibit a smooth surface of cerebellum (Klimley, 2013).
- Advanced – This form is found in bullhead, carpet, and ground sharks (these sharks are referred to as Galeoforms). These sharks have convoluted and highly foliated brains (Klimley, 2013).
The teeth of the sevengill shark also more closely resemble more prehistoric sharks. The upper jaw is made up of long, slender, hooked teeth with a central cusp and a smaller secondary cusplet. The lower jaw is made of a tall cusp with several lateral cusplets. Not only do these teeth serve the sevengill shark well in hunting other sharks, seals, bony fishes, and scavenging carrion, but they have also been used by the Maoris people of New Zealand to make weapons of war (Tricas, et al., 1997).
I saw my first broadnose sevengill shark almost two years ago now, when I visited the amazing Monterey Bay Aquarium in March of 2016. If you have not had the please of visiting Monterey, Califorina I highly recommend it. The bay is breathtakingly beautiful and I personally feel there is no better place to enjoy the view than from the observation deck and tide pools of the aquarium. But I am be slightly biased! Anyway! It was while I was visiting Monterey that I came face to face with my first broadnose sevengill – two actually. And the ladies were perfect! Enjoy a little video from that day!
Amanda Flannery. (2016 March 17). Broadnose Sevengill Sharks of Monterey Bay Aquarium [Video Clip].
Authority: Péron, 1807
Family: Hexanchidae, 5 species
Length: About 10 feet (5.04 m)
Weight: Up to 236 lbs (107 kg)
Habitat: Continental shelves and upper slopes
Depth: Ranging from depths of less than 3 feet (1 m) at the surface to 446 feet (136 m)
Gestation: Period unknown, suspected to be a year or less
Litter Range: 82 young recorded; mature female ovaries suggesting litter ranges from 67 to 104
Home Range: Temperate coastal waters of Eastern and Western Pacific Ocean, Southwestern Atlantic Ocean, Southeastern Atlantic Ocean and Indian Ocean
Diet: Other sharks, rays, bony fishes, seals, and carrion
IUCN Status: Data Deficient
(Ebert, 1996; Tricas, et al., 1997; Compagno, 2005; Skomal, 2016)
Thanks for checking out these incredible sharks this week! Remember to have a look at the Swell Shark if you missed last week’s Featured Species. If you have a species of elasmobranch you’d love to see featured, please send me a message or leave me a comment! I’d love to know what you’d like to know more about!
The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!
Remember you can make a difference for marine ecosystems by contacting your Congress man or woman and telling them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics.
Featured Image Source
Monterey Bay Aquarium. (Photographer). (n.d.) Broadnose Sevengill Shark [Digital Image]. Retrieved from http://www.montereybayaquarium.org/animal-guide/fishes/broadnose-sevengill-shark
Compagno, L.J.V. 2005. Notorynchus cepedianus. The IUCN Red List of Threatened Species 2005: e.T39324A10200310.
Ebert, D. A. (1996). Biology of the sevengill shark Notorynchus cepedianus (Peron, 1807) in the temperate coastal waters of southern Africa. South African Journal of Marine Science, 17(1), 93-103.
Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.
Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.
Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.