This week’s featured species is found in the Indian and Pacific oceans in tropical waters. The Zebra Shark (Stegostoma fasciatum) is named for its juvenile morphology, which is dark bodied with stark white stripes (Parker, 2008). However the zebra shark is also known regionally by another name- the leopard shark- for its adult stage, not to be confused with the leopard shark (Triakis semifasciata) endemic to the North American Pacific coast (Tricas, et al., 1997). As the zebra shark ages, their stripes begin to break apart and their bodies become lighter until they reach their adult form.
The zebra shark is oviparous, which means female produce egg cases, also known as a mermaid purse (Parker, 2008). These egg cases are secured to kelp beds, rocky coral ledges, even the seafloor with adhesive tendrils (Kunze & Simmons, 2004). Zebra sharks have also been documented on several occasions producing young in one of the most amazing ways, through parthenogenesis (Robinson, Baverstock, Al‐Jaru, Hyland, & Khazanehdari, 2011; Dudgeon, Coulton, Bone, Ovenden, & Thomas, 2017). This means that a female zebra shark can reproduce without the aid of a male to fertilize her young (Robinson, et al., 2011; Dudgeon, et al., 2017)! After the mother deposits her young, there is no further parental care (Parker, 2008). The young sharks develop inside the egg cases for up to 6 months, where they depend on an egg yolk for their developmental nutrients (Kunze, & Simmons, 2004). When the young are ready to enter the world, they break free of their egg cases fully formed little sharks.
Oli Underwood. (2016 February 18). Shark hatching from egg (Stegostoma fasciatum) [Video Clip]. Retrieved from https://www.youtube.com/
So why does the zebra shark go through such a dramatic change in morphology? It has been suggested that the young sharks use Batesian mimicry- or mimicry in which an edible animal resembles a noxious animal and is therefor protected from predators (Dudgeon, & White, 2012). Juvenile zebra sharks may be colored with their alternating dark and white stripes in order to mimic a toxic banded sea snake (Dudgeon, & White, 2012). This protects the small developing sharks from other larger predators like other sharks, which also may explain why this morphology is prevalent in juveniles and not present in the larger adults.
Color morphology changes are just one adaptation zebra sharks have evolved to suit their environment. The is upper lobe of the caudal fin are large and elongated with a minimal lower lobe (Parker, 2008). This tail structure is common for sharks that spend their lives near the seafloor like zebra sharks do. Their teeth are also well developed for hunting invertebrates and hard-bodied prey like crustaceans. Their teeth are small, flat, and pavement-like. The central cusp faces towards the shark’s throat, hooking on slippery prey, while the flat surface of the teeth do the crushing (Parker, 2008).
Zebra sharks are popular in zoos and aquariums, as they adapt to life in human care well (Tricas, et al., 1997). Like many species of elasmobranchs, zebra sharks have been successfully trained to respond to particular audio and visual stimuli. Check out the training that takes places between staff and sharks are Shedd Aquarium’s Wild Reef exhibit in the video clip below.
Discovery. (2008, July 17). Shark Week- Training a Shark? [Video Clip]. Retrieved from https://www.youtube.com/
Authority: Hermann, 1783
Family: Stegostomatide, 1 species
Length: Maximum of 8.2 feet (2.5 m), unsubstantiated claim of 11 feet (3.35 m)
Weight: 66 lbs (40 kg)
Habitat: Coastal waters, coral reefs, lagoons
Depth: Shallow waters to depths of 203 feet (62 m)
Reproduction: Oviparous; capable of parthenogenesis
Gestation: Young hatch from their eggs after 4 to 6 months
Litter Range: Several dozen eggs laid; have been documented laying 46 eggs in 112 days
Home Range: Tropical waters of Indian and West Pacific Oceans
Diet: Small bony fishes, invertebrates
IUCN Status: Endangered
(Dudgeon, Simpfendorfer, & Pillans, 2016; Robinson, et al., 2011; Kunze & Simmons, 2004; Parker, 2008; Skomal, 2016)
Thanks for checking out this week’s featured species! If you missed last week be sure to head over and find out more about the Frilled Shark. Haven’t seen your favorite species features here yet? Leave me a comment and let me know what species you’d love to see!
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Featured Image Source
Zebra shark [Digital Image]. (2017 January 18). Retrieved from http://chanchinthar.com/
Dudgeon, C. L., Coulton, L., Bone, R., Ovenden, J. R., & Thomas, S. (2017). Switch from sexual to parthenogenetic reproduction in a zebra shark. Scientific reports, 7, 40537.
Dudgeon, C.L., Simpfendorfer, C. & Pillans, R.D. 2016. Stegostoma fasciatum. The IUCN Red List of Threatened Species 2016: e.T41878A68645890.
Dudgeon, C. L., & White, W. T. (2012). First record of potential Batesian mimicry in an elasmobranch: juvenile zebra sharks mimic banded sea snakes?. Marine and Freshwater Research, 63(6), 545-551.
Kunze, K., & Simmons, L. (2004). Notes on reproduction of the zebra shark, Stegostoma fasciatum, in a captive environment. The Elasmobranch Husbandry Manual: Captive Care of Sharks, Rays and their Relatives, 493-497.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Robinson, D. P., Baverstock, W., Al‐Jaru, A., Hyland, K., & Khazanehdari, K. A. (2011). Annually recurring parthenogenesis in a zebra shark Stegostoma fasciatum. Journal of Fish Biology, 79(5), 1376-1382.
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.