Jeff Guertin 10/09/07 Orectolobiformes Rhincodontidae One Genus




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Jeff Guertin

10/09/07
Orectolobiformes Rhincodontidae
One Genus

  • Only one genus and species, Rhincodon typus, also known as the whale shark

  • Etymology: Greek, rhyngchos = snout, muzzle + Greek, odous, odontos = tooth, teeth

  • First identified in 1828

  • Believed to be about 60 million years old


General Characteristics


Distinctive features

  • A unique color pattern of light spots and vertical and horizontal stripes, in the form of a checkerboard

  • World’s largest fish (maximum reported length 13.7 m

  • No subterminal notch on caudal fin

  • Large first and small second dorsal fin

  • Very large pectoral fins (much larger than pelvic)


Habitat

  • Inhabitat tropical and subtropical habitats circumglobally

  • Primarily pelagic with coastal feeding aggregations at times (migrations)

  • Up to 700m

  • Usually solitary, but found in feeding aggregations of over 100 individuals


Food Habits

  • Feeds on planktonic and nektonic prey, such as small fishes (sardines, anchovies, mackerel, juvenile tunas and albacore), small crustaceans and squids

  • Have homodont teeth (all the same shape and no abrupt change in size) which is rare for sharks

  • No nictitating membrane; use the extraocular muscles to rotate the entire eye back into the orbit to protect it from abrasion during feeding

  • Ram filter feeders, where plankton is trapped against the dermal denticles. Any material caught in the filter between the gill bars is swallowed.

  • Whale sharks are highly migratory, with their movements probably timed with blooms of planktonic organisms and changes in temperatures of water masses

    • During March and April, they aggregate on the continental shelf of central western Australian coast in response to coral spawning events that occur each year

    • Make regular oscillations between the surface and the bottom off the coast, probably to search for food throughout the water column


Size, Age, Growth

  • Average size is 8m, can grow up to 12.5m; largest specimen regarded as accurately recorded was caught in 1947 near India (12.65m, ~47,00lbs)

    • Reports of specimen as large as 18m

  • Little known about age and growth rates

    • Age estimates unknown, but thought to be well over 60 years (maybe upwards of 100)

    • Females as large as 8-9m have been found to be immature


Reproduction

  • Originally thought to be oviparous, but in 1995 a female was harpooned off the coast of Taiwan which showed that they are ovoviviparous; litter size was over 300 pups

    • Sex ratio was about 1:1

  • Give birth to pups 40-60cm big

  • Sexual maturity estimated at 30 years of age, but really unknown


Predators

  • Some whales and dolphins (killer whales)

  • A juvenile specimen was found in the stomach of a blue shark (Prionace glauca). Another specimen was found in the gut contents of a blue marlin (Makaira nigricans).

  • Humans


Conservation

  • Utilized fresh, frozen, dried and salted for human consumption, liver processed for oil, fins used for shark-fin soup, cartilage for health supplements and skin for leather products

  • Used in Chinese medicine

  • Status is vulnerable


Bibliography
1) Carrier J, Musick J, Heithaus M. 2004. Biology of Sharks and their Relatives. CRC Press, Boca Raton, FL, pp. 38-67, 167-187, 227, 327, 419, 496-500.
2) Compagno, L.J.V., 1984. FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 1 - Hexanchiformes to Lamniformes. FAO Fish. Synop. 125(4/1):1-249.
3) Florida Museum of National History. Accessed online 03 October 2007 at http://www.flmnh.ufl.edu/fish/Gallery/Descript/Whaleshark/whaleshark.html.
4) IUCN 2006. 2006 IUCN Red List of Threatened Species. Accessed online 03 October 2007 at www.iucnredlist.org.
5) Norman B & Stephens J. 2007. Size and maturity status of the whale shark (Rhincodon typus) at Ningaloo Reef in Western Australia. Fisheries Science 84, 81-86.
6) Taylor, J. 1996. Seasonal occurrence, distribution and movements of the whale shark, Rhincodon typus, at Ningaloo Reef, Western Australia. Marine and Freshwater Research 47, 637–642.
7) Whale Shark Project. Accessed online 03 October 2007 at http://www.whalesharkproject.org/.


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