- Thresher shark
Taxobox
name = Thresher shark
fossil_range = Fossil range|56|0 EarlyEocene to Present [cite journal
last = Sepkoski
first = Jack
authorlink =
coauthors =
title = A compendium of fossil marine animal genera (Chondrichthyes entry)
journal = Bulletins of American Paleontology
volume = 364
issue =
pages = p.560
publisher =
location =
date = 2002
url = http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=575&rank=class
doi =
id =
accessdate = 2008-01-09 ]
image_width = 200px
image_caption =Pelagic thresher , "Alopias pelagicus"
status = VU
regnum =Animal ia
phylum = Chordata
classis =Chondrichthyes
subclassis =Elasmobranchii
ordo =Lamniformes
familia = Alopiidae
familia_authority = Bonaparte, 1838
genus = "Alopias"
genus_authority = Rafinesque, 1810
subdivision_ranks = Species
subdivision = For species see text.Thresher sharks are large
lamniform shark s of the family Alopiidae. Found in all temperate and tropicalocean s of the world, the family contains threespecies all within thegenus "Alopias".Naming
The genus and family name derive from the Greek word "alopex", meaning
fox . Indeed thelong-tailed thresher shark , "Alopias vulpinus", is named the fox shark by some authorities.Distribution and habitat
Although occasionally sighted in shallow, inshore waters, thresher sharks are primarily pelagic; they prefer the open ocean, staying within the first 500 m of the
water column . Common threshers tend to be more common in coastal waters over continental shelves. In the North Pacific, common thresher sharks are found along the continental shelves of North America and Asia. They are rare in the Central and Western Pacific. In the warmer waters of the Central & Western Pacific, bigeye and pelagic thresher sharks are more common.Anatomy and appearance
[
Small purple colored thresher caught atPacifica Pier ,California .] Named for and easily recognised by their exceptionally long,thresher -like tail or "caudal fin s" (which account for 1/3 of their total body length), thresher sharks are active predators; the tail is actually used as a weapon to stun prey. By far the largest of the three species is theCommon thresher , "Alopias vulpinus", which may reach a length of 20 ft and aweight of over 500 kg. TheBigeye thresher , "Alopias superciliosus", is next in size, reaching a length of 4.9 m (16 ft); at just 3 m (10 ft), thePelagic thresher , "Alopias pelagicus", is the smallest.Thresher sharks are fairly slender, with small dorsal fins and large, recurved pectoral fins. With the exception of the Bigeye thresher, these sharks have relatively small eyes. Coloration ranges from brownish, bluish or purplish gray dorsally with lighter shades ventrally.The three species can be roughly distinguished by the main color of the dorsal surface of the body. Common threshers are dark green, Bigeye threshers are brown and Pelagic threshers are generally blue. Lighting conditions and water clarity can affect how any one shark appears to an observer, but the color test is generally supported when other features are examined.
Diet
Pelagic schooling fish (such as bluefish, juvenile tuna, and mackerel), squid and cuttlefish are the primary food items of the thresher sharks. They are known to follow large schools of fish into shallow waters. Crustaceans and the odd seabird are also taken.
Behavior
Thresher sharks are solitary creatures which keep to themselves. It is known that thresher populations of the
Indian Ocean are separated by depth and space according to gender. All species are noted for their highly migratory oroceanodromous habits.Thresher sharks are one of the few shark species known to jump fully out of the water making turns like
dolphin s, this behaviour is called breaching.Reproduction
No distinct breeding season is observed by thresher sharks. Fertilization and embryonic development occur internally; this ovoviviparous or live-bearing mode of reproduction results in a small litter (usually 2 to 4) of large well-developed pups, up to 150 cm at birth in thintail threshers. The young fish exhaust their yolk sacs while still inside the mother, at which time they begin feeding on the mother's unfertilized eggs; this is known as
oophagy .Thresher sharks are slow to mature, males reaching sexual maturity between 7 and 13 years of age and females between 8 and 14 years in bigeye threshers. They may live for 20 years or more.
Conservation
All three thresher shark species have been recently listed as vulnerable to extinction by the
World Conservation Union (IUCN). [cite press release |title=More oceanic sharks added to the IUCN Red List |publisher=IUCN |date=2007-02-22 |url=http://www.iucn.org/en/news/archive/2007/02/22_pr_sharks.htm |format= |language= |accessdate=2007-02-25 |quote= ]Importance to humans
Like all large sharks, threshers are slow growing and are therefore threatened by commercial fisheries. Other than for its meat, the sharks are hunted for their liver oil, skin (for leather), and their fins, for use in
shark-fin soup .
Wikimedia Foundation. 2010.