Sharks, skates, and rays, which together form a group of about 900-1150 species(1,2) of ocean-dwelling and freshwater-dwelling fish(3,4) called elasmobranchs,(1) are some of the most fascinating creatures of the deep. While they come in many sizes and shapes—from the giant whale shark(5) and the huge manta ray (3) to the dwarf lanternshark(6) and the tiny short-nosed electric ray,(3) and the from the odd-looking hammerhead sharks(4) to the totally bizarre sawfish(3)—all living elasmobranchs share certain key features. First of all, their skeletons are made up of a strong, flexible, and light material called cartilage,(7) rather than bone, making them (along with another fish group called chimaeras(1)) fundamentally different from other fish.(1,3,8) Other important characteristics include their rows of replaceable teeth(2) and the 5-7 gill slits on each side of their body.(3) In addition, although these creatures are ancient—the first elasmobranchs evolved at least 400 million years ago!(1,5,8,9)—they have many highly-developed senses,(4,10) including the amazing ability to perceive tiny changes in electricity around them.(10,11) Sharks, as well as rays and skates (which you can tell apart from sharks by their generally flattened, diamond-shaped bodies(3)), often use this sense for finding prey, as well as for finding their way through the water.(10,11) In at least some elasmobranchs this sense may even be used in various social and mating behaviors.(11) In part thanks to this electric sense, many elasmobranchs are skillful hunters, often serving as the top predators in the food chain and keeping their environments in the proper balance.(9,12,13) These creatures also have an important relationship with humans. Some rays, such as stingrays and electric rays, can cause injury to people.(3,4) And even if you haven’t heard much about the dangers of those fish, you’ve definitely heard of shark attacks, which have given sharks a very dark reputation even though these attacks are actually rare.(4,12,14) In fact, although elasmobranchs can pose dangers to humans, humans pose a much greater danger to them.(13) For over 5000 years shark meat has been eaten by people,(8) and ray meat, skate meat, shark skin, and other elasmobranch products are also sometimes used by humans today.(3,8,13) Overfishing, accidental catching (called “bycatch”),(1,9,13,15,16) higher numbers of people living on the coast, and greater damage to coastal environments(13,15) are all threatening sharks, skates, and rays. And because elasmobranchs generally grow slowly, reproduce late in life, and have only a small number of children, they have trouble recovering from population decline caused by humans.(1,5,8,12,13,15) As a result, many elasmobranchs around the world are endangered.(13,15)
- 1. Kyne, Peter M. and Colin A. Simpfendorfer. “A Collation and Summarization of Available Data on Deepwater Chondrichthyans: Biodiversity, Life History and Fisheries.” IUCN SSC Shark Specialist Group. 2007.
- 10. Bleckmann, Horst and Michael H. Hofmann. “Special Senses.” Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes. Ed. William C. Hamlett. Baltimore: Johns Hopkins University Press, 1999.
- 11. Tricas, T. C. and J. G. New. “Sensitivity and Response Dynamics of Elasmobranch Electrosensory Primary Afferent Neurons to Near Threshold Fields.” Journal of Comparative Physiology A—Sensory Neural and Behavioral Physiology 182.1 (1998): 89-101.
- 12. Branstetter, Steven, ed. NOAA Technical Report NMFS 115: Conservation Biology of Elasmobranchs. Springfield: U.S. Department of Commerce, 1993.
- 13. Simpfendorfer, C. A., M. R. Heupel, W. T. White, and N. K. Dulvy. “The Importance of Research and Public Opinion to Conservation Management of Sharks and Rays: A Synthesis.” Marine and Freshwater Research 62.6 (2011): 518-527.
- 14. “Shark Attacks in Perspective.” Florida Museum of Natural History Ichthyology Department: Sharks. International Shark Attack File. 1991. 21 Jul. 2011. http://www.flmnh.ufl.edu/fish/sharks/Attacks/perspect.htm
- 15. Cavanagh, Rachel D. and Claudine Gibson. Overview of the Conservation Status of Cartilaginous Fishes (Chondrichthyans) in the Mediterranean. Malaga: IUCN, 2007.
- 16. Ebert, David A. and James A. Sulikowski. “Preface: Biology of Skates.” Environmental Biology of Fishes 80.2-3 (2007): 107-110.
- 2. Compagno, Leonard J. V. “Systematics and Body Form.” Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes. Ed. William C. Hamlett. Baltimore: Johns Hopkins University Press, 1999.
- 3. Bester, Cathleen. “Ray and Skate Basics.” Florida Museum of Natural History Ichthyology Department: Education. 7 Sept. 2011. http://www.flmnh.ufl.edu/fish/education/questions/raybasics.html
- 4. “Know Before You Go – Marine Animals.” Wet Tropics Visitor Information. Wet Tropics Management Authority. 2010. 7 Sept. 2011. http://www.wettropics.gov.au/vi/vi_marine.html
- 5. Hoenig, John M. and Samuel H. Gruber. “Life-History Patterns in the Elasmobranchs: Implications for Fisheries Management.” NOAA Technical Report NMFS 90: Elasmobranchs as Living Resources: Advances in the Biology, Ecology, Systematics, and the Status of the Fisheries. Harold L. Pratt, Jr., Samuel H. Gruber, and Toru Taniuchi, eds. Springfield: U.S. Department of Commerce, 1990.
- 6. Martin, R. Aidan. “Order Squaliformes: Dogfish Sharks – 119 Species.” ReefQuest Centre for Shark Research. 21 Jul. 2011. http://www.elasmo-research.org/education/shark_profiles/squaliformes.htm
- 7. Martin, R. Aidan. “The Importance of Being Cartilaginous.” ReefQuest Centre for Shark Research. 21 Jul. 2011.
- 8. Schubring, Reinhard. “DSC Measurements on Sharks.” Thermochimica Acta 458.1-2 (2007): 124-131.
- 9. “Sharks: Overview.” Oceana. 2010. 25 Jul. 2011. http://na.oceana.org/en/our-work/protect-marine-wildlife/sharks/overview