This week’s featured species is a strikingly beautiful species from the Northwestern Pacific Ocean. The Japanese Bullhead Shark (Heterodontus japonicus) is a small shark, typically reaching lengths of 3.5 feet (1.2 m). They have stocky, blunt heads with prominent eye ridges (Ebert, Fowler, & Dando, 2015). As juveniles, they have 12 irregular dark saddle-like bands along their bodies. As they age, the vivid bands become lighter in color. They also have sharp spines that along the leading edge of each tall dorsal fin. The Japanese bullhead shark uses these spines for defense against larger predators.
Underwater Video JP (Videographer). (2016 May). ネコザメ Japanese Bullhead Shark [Video Clip]. Retrieved from https://www.youtube.com/
The Japanese bullhead shark is a member of the Order Heterodontiformes, in the Family Heterodontidae (Skomal, 2016). Today there are 9 extant species within this family that includes the horn sharks and the bullhead sharks.
- California horn shark (Heterodontus francisci)
- Mexican horn shark (Heterodontus mexicanus)
- Port Jackson shark (Heterodontus portusjacksoni)
- Crested bullhead shark (Heterodontus galeatus)
- Zebra bullhead shark (Heterodontus zebra)
- Whitespotted bullhead shark (Heterodontus ramalheira)
- Galapagos bullhead shark (Heterodontus quoyi)
- Oman bullhead shark (Heterodontus omanensis)
- and the Japanese bullhead shark (Heterodontus japonicus)
Heterodontidae sharks are characterized by a pig-like snout with a small mouth that is completely anterior to their eyes; a caudal in with a conspicuous subterminal lobe; very distinct brow ridges above the eyes; spines along the leading edge of the dorsal fins; and the presence of different teeth morphology throughout the jaw (Ebert, Fowler, & Dando, 2015).
As I mentioned above, Heterodontidae sharks are known for having different teeth morphology throughout their jaws. The name Heterodontidae means different, or other, (“hetero-“) teeth (“dont”). The Japanese bullhead shark is no exception. In the anterior, or front, part of the jaw, they have short but very sharp teeth that are designed to grab and pull their prey into their mouths. The posterior, or back, of the jaw is made of flat, pavement-like teeth that are made for crushing their favorite prey items (Klimley, 2013). Like many other members of Heterodontidae, the Japanese bullhead shark prefers benthic prey items including mollusks, small fishes, crustaceans, and sea urchins (Smith, 1942).
The Japanese bullhead shark is a relatively fecund shark, meaning they are capable of producing a relatively high number of offspring. One of the reasons for their high fecundity is because they are oviparous, or egg layers. Each year between March and September, mature females lay pairs of corkscrew shaped eggs at depths around 26 to 29 feet (8 to 9 m) (Smith, 1942; Compagno, 2001). A female will continue to deposit pairs of eggs in 6 to 12 spawnings throughout the six month breeding season (Smith, 1942).
The Japanese bullhead shark is found in a relatively small region in the temperate kelp beds and rocky inshore habitats of the Northwestern Pacific Ocean. Throughout this region, the Japanese bullhead shark is subjected to pollution from terrestrial runoff. This area is also being closely monitored following the Fukushima Nuclear Accident that occurred as a result of the tsunami on March 11, 2011 (Men, He, Wang, Wen, Li, Huang, & Yu, 2015). The full extent of the impacts on the region and its species are not fully understood and it may take decades before we do. The Japanese bullhead shark is also taken in commercial fisheries as bycatch (Tanaka & Nakaya, 2009). While the Japanese bullhead shark is not directly targeted by these fisheries, they are sometimes caught in gillnets and by other inshore fisheries. To date, the Japanese bullhead shark is categorized as Least Concern by the International Union for the Conservation of Nature (IUCN) and no current conservation measures are in place for this species specifically (Tanaka & Nakaya, 2009). However, the quality of their habitat should be closely monitored throughout the region to be able to reassess any potential threats.
Authority: Miklouho-Maclay & Macleay, 1884
Family: Heterodontidae; 9 species
Length: Up to 3.9 feet (1.2 m)
Weight: Maximum weight unknown
Habitat: Temperate Intertidal zones
Depth: 20 – 122 feet (6 – 37 m)
Gestation: Approximately 12 months
Litter Range: Females deposit 2 eggs during 6 to 12 spawnings from March to September
Home Range: Temperate Northwestern Pacific Ocean
Diet: Molluscus, small fish, sea urchins
IUCN Status: Least Concern
(Smith, 1942; Tanaka & Nakaya, 2009; Ebert, Fowler, & Dando, 2015; Skomal, 2016)
Thanks so much for checking out the Japanese Bullhead Shark! If you missed last week’s featured species, please be sure to check out the charming Whitespotted Bamboo Shark! If there is a species of elasmobranch you’d love to know more about, leave me a comment or send me a message! I would love to do a feature on your favorite species. So connect with me on Instagram and Facebook for even more elasmo fun!
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!
Conservation legislation needs public support in order to become law and help protect the environment and wildlife. Tell your representatives that you care about environmental and wildlife conservation. It only takes a moment to make a change that will last a lifetime. Until next time finactics!
Featured Image Source
Yzx (photographer). (2013 May). Japanese bullhead shark (Heterodontus japonicus) at the Port of Nagoya Aquarium [Digital Image]. Retrieved from https://commons.wikimedia.org/
Compagno, L. J. (2001). Sharks of the world. An annotated and illustrated catalogue of shark species known to date, vol 2. Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). FAO species catalogue for fishery purposes, 1, viii+-1.
Ebert, D. A., Fowler, S. L., & Dando, M. (2015). Sharks of the world: a fully illustrated guide. Wild Nature Press.
Men, W., He, J., Wang, F., Wen, Y., Li, Y., Huang, J., & Yu, X. (2015). Radioactive status of seawater in the northwest Pacific more than one year after the Fukushima nuclear accident. Scientific reports, 5, 7757.
Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.
Smith, B. G. (1942). The Heterodon Tid Sharks: Their Natural History, and the External Development of” Heterodontus Japonicus” Based on Notes and Drawings by Bashford Dean. By Bertram G. Smith,... American Museum of natural history.
Tanaka, S. & Nakaya, K. 2009. Heterodontus japonicus. The IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/161714/5486896