This week’s Featured Species profile is going to the cats, well catsharks. The chain catshark (Scyliorhinus retifer) is sometimes referred to as the chain dogfish; however, they are a member of the family Scyliorhinidae, which is a family of ground sharks containing over 150 species of catsharks (Skomal, 2016). These catsharks are relatively small, reaching only 2 feet (0.6 m) when fully grown. Their bodies are elongated, with their first dorsal fin placed above or behind the pelvic fins. Their caudal fin has no strong ventral lobe, but instead is essentially an elongated upper lobe, which is common among benthic – or bottom dwelling – sharks. They also have large spiracles to aid in breathing when resting on the bottom for long periods (Stevens, 1997). The chain catshark has a beautiful, distinctive chain-like pattern over its back.
Chain catsharks are oviparous, meaning they are egg layers. A female chain catshark can produce between 44 to 52 eggs per year (Skomal, 2016). She lays these purse-like egg cases, which are often referred to as mermaid’s purses, with long tendrils protruding from both sides. These tendrils catch in corals, rocks, kelp beds, and other substrates. This anchors the egg for the next 7 months while the embryo develops inside (Tricas, et all., 1997). When the hatchlings are fully formed, they emerge from their egg cases, ready to hunt small bony fishes and invertebrates (Skomal, 2016).
In recent years, scientists have begun exploring the oceans for biofluorescent organisms. Biofluorescence is the process in which animals absorb light, transform it, and emit it back as another color. This process is different than bioluminescence, where organisms produce and emit their own light (Gruber, et al., 2016). Thus far, biofluorescence has been discovered in corals, several species of bony fishes, invertebrates, reptiles, and some elasmobranchs. The only two shark species known to biofluoress are catsharks: the swellshark (Cephaloscyllium ventriosum), and the chain catshark (Scyliorhinus retifer). It is still unclear what exactly these sharks use biofluorescence for. It is thought it may aid in mate detection, identifying of conspecifics, and even territorial claims (Gruber, et al., 2016).
We know from recent studies that some inferences can be made about shark behavior based on the size and structure of the brain (Klimley, 2013). A particularly important region of the brain is the telencephalon, which makes up part of the forebrain that coordinates sensory information and allows an individual to respond to stimuli (Klimley, 2013). There are 4 different portions of the brain that process sensory information:
- The Olfactory Bulb (OB) which is used in chemoreception.
- The Posterior Lateral Line Lobes (PLLLs) which is used in mechanoreception.
- The Optic Tectum (OT) which processes photoreception.
- And The Anterior Lateral Line Lobes (ALLLs) which processes electroreception.
In the chain catshark, the optic tectum contributes only 21% of the brain, which implies that this species uses its sight less in a dark, deep water environment than species found in shallower waters (Hart, Lisney, & Collin, 2006). The olfactory bulb, however, makes up a larger proportion of the brain, roughly 62%, suggesting that the chain catshark relies more heavily on its sense of small to locate prey (Hart, et al., 2006).
Over recent decades, global large shark populations have been on the decline due to pressures from the fisheries industries. Many large shark species, like the bull shark (Carcharhinus leucas), the tiger shark (Galeocerdo cuvier), and the scalloped hammerhead (Sphyrna lewini), have seen dramatic population declines over the last 30 years or so. With a reduction in predation from large sharks, smaller mesopredaters, like the sharpnose shark (Rhizoprionodon terraenovae), cownose ray, (Rhinoptera bonasus), and the chain catshark, have seen population increases. As adults, chain catsharks live in deep water between 240 – 2474 feet (73 – 754 m) and they prefer rough ground like rocky outcroppings (Sherrill-Mix, Myers & Burgess, 2006). This makes trawling them for commercial fisheries very difficult. Typically when these sharks are caught as bycatch they are juveniles, which suggests that populations are separated by age and size (Sherrill-Mix, et al., 2006). Chain catsharks are one of the few deep water species that have thrived in captivity. Pressures from the aquarium trade are not thought to have a dramatic impact on populations due to their wide distribution in the Atlantic Ocean, their habitat preference as adults offering refuge from fisheries, and their relatively high fecundity. Currently these sharks are listed at Least Concern by the IUCN (Sherrill-Mix, et al., 2006).
Authority: Garman, 1881
Family: Scyliorhinidae, 149+ species
Length: 2 feet (0.6 m)
Weight: Maximum weight unknown
Habitat: Continental shelves and slopes
Depth: Between 240 – 2474 feet (73 – 754 m)
Gestation: 7 months
Litter Range: 44 – 52 eggs per year
Home Range: Tropical and temperate waters in the Western Atlantic
Diet: Small bony fishes and invertebrates
IUCN Status: Least Concern
(Tricas, et al., 1997; Compagno, Dando, & Fowler, 2005; Sherrill-Mix, et al., 2006 Skomal, 2016)
Thank you for checking out this week’s featured species. In case you missed last week’s beautiful Deepsea Skate Featured Species post!
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!
As always, 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
Murch, A. (Photographer). (n.d.) Chain catshark [Digital Image]. Retrieved from http://www.elasmodiver.com/
For more information visit Shark Reference.
Compagno, L., Dando, M. and Fowler, S. 2005. A field guide to the sharks of the world. Harper Collins Publishers Ltd., London.
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.
Hart, N. S., Lisney, T. J., & Collin, S. P. (2006). Visual communication in elasmobranchs. Communication in fishes, 2, 337-392.
Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.
Sherrill-Mix, S.A., Myers, R.A. & Burgess, G.H. 2006. Scyliorhinus retifer. The IUCN Red List of Threatened Species 2006: e.T60233A12331224.
Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.
Stevens, J. D. (Ed.). (1997). Sharks (6th ed.). New York: Facts on File.
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.