This week’s featured species is a deep water shark that is straight out of a sci-fi film. The Viper Dogfish (Trigonognathus kabeyai) is a member of the family Etmopteridae, which is the largest family of squaloid sharks with over fifty species in four genera. There is some debate on whether this family should be broken up into two clades; however, at present, the family Etmopteridae consists of the lanternsharks in genus Emtoperus, the hooktooth dogfish of Aculeola, a variety of dogfishes in genus Centroscyllium, and the viper dogfish of Trigonognathus (Ebert, Fowler, & Dando, 2015). Like most sharks in this family, the viper dogfish is a small species of shark, only reaching lengths around 1.77 feet (0.54 m) and weighs a mere 1.7 lbs (0.76 kg) (Yano, Mochizuki, Tsukada, & Suzuki, 2003). They have large eyes with deep pockets in front of very large spiracles. Their dorsal fins are low with grooved spines along the leading edges. They are known for their very long snake-like mouths with huge curved fang-like teeth, resembling a viper (Ebert, Fowler, & Dando, 2015).
The viper dogfish is a rarely encountered species, living at depths around 820 to 3280 feet (250 to 1000 m). This shark was first discovered in 1986 when two immature males were caught by a bottom trawler off southern Japan; and it was first described in 1990 for the Japanese Journal of Ichthyology (Mochiuki & Ohe, 1990).Today, their known distribution is limited to the upper continental slopes of southern Japan and Taiwan, with a single sighting documented in Hawaii in 2000 (Wetherbee, & Kajiura, 2000). Because of their rarity, very little is known about their biology, ecology, or behavior.
Many deep sea elasmobranchs, like the viper dogfish, have the ability to produce light through light producing organs called photophores. These photophores are scattered across the underside of the viper dogfish’s body (Yano, Mochizuki, Tsukada, & Suzuki, 2003). These bioluminescent organs allow for the viper dogfish to blend seamlessly into the light coming from the surface above when viewed from below (Parker, 2008). That’s a pretty neat trick in my book! This comes in pretty handy when they enter shallower waters to feed at night. The photophores make them all but invisible against the light of the moon and the dark water. The bioluminescence of the viper dogfish is different than the biofluorescence found in the swellshark (Cephaloscyllium ventriosum) and the chain catshark (Scyliorhinus retifer). Biofluorescence is the process in which animals absorb light, transform it, and emit it back as another color; they do not produce light themselves (Gruber, et al., 2016).
Discovery (Videographer). (2015). Glow-in-the-dark Sharks [Video Clip]. Retrieved from https://www.youtube.com/
The viper dogfish performs diel vertical migrations, meaning they spend their days in deep waters, and migrate vertically in the water column at night into shallower waters to feed (Yano, Mochizuki, Tsukada, & Suzuki, 2003). Their prey, small myctophid lantern fishes, also perform these migrations. To catch these small, slippery lantern fish, the viper dogfish has wicked set of teeth. Their teeth are distinctively fang-like and spaced far apart. In the lower jaw, they have seven to ten tooth rows on each side of the jaw, and six to ten tooth rows in the upper jaw. Interestingly, they have a single mid-line tooth row in each jaw. Some shark species have small mid-line teeth; however, these teeth in the viper dogfish are large and overlap when the jaw is closed, while the lateral teeth interlock. The teeth of the viper dogfish are narrow and recurved, perfectly adapted for grasping prey over cutting through flesh. Much like the goblin shark (Mitsukurina owstoni), during feeding, the lower jaw extends down in a snake-like fashion, while the free-floating top jaw protrudes forward from the bottom of the skull. Then both jaws snap forward and down rapidly, trapping its prey behind its teeth where it is swallowed whole. Using this feeding method, the viper dogfish can consume prey nearly 40% as long as itself (Yano, Mochizuki, Tsukada, & Suzuki, 2003).
The viper dogfish is currently categorized as a Data Deficient species by the International Union for the Conservation of Nature (IUCN). Due to its rarity, its population size, structure, and trends are unknown, as is much of its biology, ecology, and life history characteristics. As fisheries move further and further into deep water habitats, the potential implications for their populations is still unclear. At present, this species is still incredibly rare even as bycatch within these industries. There are no conservation actions in place for this species at the time of this writing. More scientific data is needed to assess the conservation status of this species and its need for conservation action (Yano, 2004).
I’m delighted to announce a partnership with the wonderfully talented Julius Csotonyi! Julius creates stunning shark coloring sheets that are fun and educational for all ages. From time to time you’ll see Julius’ work featured right here and on my other social media platforms! You can find more coloring sheets in the store! You are welcomed to download these beautiful sheets and enjoy them with family and friends.
Authority: Mochiuki & Ohe, 1990
Family: Etmopteridae, 50+ species
Length: 1.77 feet (0.54 m)
Weight: 1.7 lbs (0.76 kg)
Habitat: Upper continental slopes
Depth: 820 – 3280 feet (250 – 1,000 m)
Reproduction: Yolk Sac Viviparity
Litter Range: Likely under 26
Home Range: Limited distribution around Japan, single report in Hawaii, recently discovered in Taiwan
Diet: Myctophid fishes
IUCN Status: Data Deficient
(Yano, Mochizuki, Tsukada, & Suzuki, K. 2003; Yano, 2004; Ebert, Fowler, & Dando, 2015)
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. Proceeds benefit shark research and conservation with a donation to Project AWARE!
Thanks so much for checking out the alien Viper Dogfish! If you missed last week’s featured species, please be sure to check out the angelic and devilish Giant Devil Ray! 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. Also connect with me on Instagram and Facebook for even more elasmo fun!
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
Hsuan-Ching, H. (Photographer). (2018). The viper dogfish (Trigonognathus kabeyai) [Digital Image]. Retrieved from https://img.purch.com/
Ebert, D. A., Fowler, S. L., & Dando, M. (2015). Sharks of the world: a fully illustrated guide. Wild Nature Press.
Gruber, D. F., Loew, E. R., Deheyn, D. D., Akkaynak, D., Gaffney, J. P., Smith, W. L., … & Sparks, J. S. (2016). Biofluorescence in catsharks (Scyliorhinidae): fundamental description and relevance for elasmobranch visual ecology. Scientific reports, 6, 24751.
Wetherbee, B. M., & Kajiura, S. M. (2000). Occurrence of a rare squaloid shark, Trigonognathus kabeyai, from the Hawaiian Islands.
Mochizuki, K., & Ohe, F. (1990). Trigonognathus kabeyai, a new genus and species of the squalid sharks from Japan. Japanese Journal of Ichthyology, 36(4), 385-390.
Yano, K. 2004. Trigonognathus kabeyai. The IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/44205/10870401
Yano, K., Mochizuki, K., Tsukada, O., & Suzuki, K. (2003). Further description and notes of natural history of the viper dogfish, Trigonognathus kabeyai from the Kumano-nada Sea and the Ogasawara Islands, Japan (Chondrichthyes: Etmopteridae). Ichthyological Research, 50(3), 251-258.