World Library  
Flag as Inappropriate
Email this Article

Thresher shark

Article Id: WHEBN0000554877
Reproduction Date:

Title: Thresher shark  
Author: World Heritage Encyclopedia
Language: English
Subject: Lamniformes, Pelagic thresher, Bigeye thresher, Shark, Fish fin
Collection: Alopiidae, Commercial Fish, Monogeneric Animal Families, Ovoviviparous Fish, Sport Fish, Ypresian First Appearances
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Thresher shark

Thresher shark
Temporal range: 49–0 Ma[1]
Є
O
S
D
C
P
T
J
K
Pg
N
Lutetian to Recent
Pelagic thresher (A. pelagicus)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Selachimorpha
Order: Lamniformes
Family: Alopiidae
Bonaparte, 1838
Genus: Alopias
Rafinesque, 1810
Type species
Alopias macrourus
Rafinesque, 1810
Synonyms
  • Alopecias Müller and Henle, 1837
  • Alopius Swainson, 1838
  • Vulpecula Jarocki, 1822

Thresher sharks are large lamniform sharks of the family Alopiidae found in all temperate and tropical oceans of the world; the family contains four species, all within the genus Alopias.

Contents

  • Taxonomy 1
    • Species 1.1
  • Phylogeny and evolution 2
  • Distribution and habitat 3
  • Anatomy and appearance 4
  • Diet 5
  • Behavior 6
  • Endothermy 7
  • Reproduction 8
  • Importance to humans 9
  • Conservation 10
  • See also 11
  • References 12
  • External links 13

Taxonomy

The genus and family name derive from the Greek word alopex, meaning fox. As a result, the long-tailed or common thresher shark, Alopias vulpinus, is also known as the fox shark.[2] The common name is derived from a distinctive, thresher-like tail or caudal fin which can be as long as the body of the shark itself.

Species

The three extant thresher shark species are all in the genus Alopias. The possible existence of a hitherto unrecognized fourth species was revealed during the course of a 1995 allozyme analysis by Blaise Eitner. This species is apparently found in the eastern Pacific off Baja California, and has previously been misidentified as the bigeye thresher. So far, it is only known from muscle samples from one specimen, and no aspect of its morphology has been documented.[3]

Phylogeny and evolution



Megachasmidae


voidAlopiidaevoid

A. vulpinus



undescribed Alopias sp.



A. superciliosus


A. pelagicus






Cetorhinidae


Lamnidae




Phylogeny of Alopiidae[3][4]

Based on cytochrome b genes, Martin and Naylor (1997) concluded the thresher sharks form a monophyletic sister group to the clade containing the families Cetorhinidae (basking shark) and Lamnidae (mackerel sharks). The megamouth shark (Megachasma pelagios) was placed as the next-closest relative to these taxa, though the phylogenetic position of that species has yet to be resolved with confidence. Cladistic analyses by Compagno (1991) based on morphological characters, and Shimada (2005) based on dentition, have both corroborated this interpretation.[4][5]

Within the family, an analysis of allozyme variation by Eitner (1995) found the common thresher is the most basal member, with a sister relationship to a group containing the unrecognized fourth Alopias species and a clade comprising the bigeye and pelagic threshers. However, the position of the undescribed fourth species was only based on a single synapomorphy (derived group-defining character) in one specimen, so some uncertainty in its placement remains.[3]

Distribution and habitat

Although occasionally sighted in shallow, inshore waters, thresher sharks are primarily pelagic; they prefer the open ocean, venturing no deeper than 500 metres (1,600 ft). Common threshers tend to be more common in coastal waters over continental shelves. Common thresher sharks are found along the continental shelves of North America and Asia of the North Pacific, but are rare in the Central and Western Pacific. In the warmer waters of the Central and Western Pacific, bigeye and pelagic thresher sharks are more common. A thresher shark was seen on the live video feed from one of the ROVs monitoring BP's Macondo oil well blowout in the Gulf of Mexico. This is significantly deeper than the 500m previously thought to be their limit.

Anatomy and appearance

Small purple colored thresher caught at Pacifica Pier, California

Named for their exceptionally long, thresher-like heterocercal tail or caudal fins (which can be as long as the total body length), thresher sharks are active predators; the tail is used as a weapon to stun prey. The thresher shark has a short head and a cone-shaped nose. The mouth is generally small, and the teeth range in size from small to large.[6] By far the largest of the three species is the common thresher, Alopias vulpinus, which may reach a length of 6.1 metres (20 ft) and a weight of over 500 kilograms (1,100 lb). The bigeye thresher, Alopias superciliosus, is next in size, reaching a length of 4.9 m (16 ft); at just 3 m (10 ft), the pelagic 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 positioned to the forward of the head. Coloration ranges from brownish, bluish or purplish gray dorsally with lighter shades ventrally.[7] 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 occasionally seabirds are also taken.

Behavior

External video
Stunning tail: Thresher sharks evolved to slap and kill their prey – NBC News

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 sex. Some species however do occasionally hunt in a group of two or three contrary to their solitary nature. All species are noted for their highly migratory or oceanodromous habits. When hunting schooling fish, thresher sharks are known to "slap" the water, herding and stunning prey.[7] The elongated tail is used to swat smaller fish, stunning them before feeding.[8] Thresher sharks are one of the few shark species known to jump fully out of the water, making turns like dolphins; this behavior is called breaching.

Endothermy

Two species of the thresher have been identified as having a modified circulatory system that acts as a counter-current heat exchanger, which allows them to retain metabolic heat. Mackerel sharks (Lamnidae family) have a similar homologous structure to this which is more extensively developed. This structure is a strip of red muscle along each of its flanks, which has a tight network of blood vessels that transfer metabolic heat inward towards the core of the shark, allowing it to maintain and regulate its body heat.

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 two to four) 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 reach sexual maturity between seven and 13 years of age and females between eight and 14 years in bigeye threshers. They may live for 20 years or more. In October 2013, the very first picture of a Thresher shark giving birth was taken by Attila Kaszo off the coast of the Philippines. http://www.msn.com/en-ca/news/techandscience/rare-shark-birth-photographed-for-the-first-time/ar-AA88wgt?ocid=mailsignoutmd

Importance to humans

Threshers have a low fecundity, like all large sharks, and are highly vulnerable to overfishing. Besides being hunted for their meat, threshers are also hunted for their liver oil, skin (for leather), and their fins, for use in shark-fin soup.

They do not appear to be a threat to humans, although some divers have been hit with the upper tail lobe. A dubious account of a fisherman being decapitated by a tail swipe as the shark breached has been reported.[9]

Thresher sharks are classified as prized game fish in the United States and South Africa. Common thresher sharks are the target of a popular recreational fishery off Baja, Mexico. Thresher sharks are farmed in some areas for their value as both a recreational sport fish and for commercial products derived from their flesh.

Conservation

All three thresher shark species have been listed as vulnerable to extinction by the World Conservation Union since 2007 (IUCN).[10]

See also

References

  • "Alopias".  
  • Froese, Rainer, and Daniel Pauly, eds. (2011). AlopiasSpecies of in FishBase. February 2011 version.
  1. ^ Bourdon, J. (April 2009). AlopiasFossil Genera: . The Life and Times of Long Dead Sharks. Retrieved on October 6, 2009.
  2. ^ "fox shark - shark species". Encyclopedia Britannica. 
  3. ^ a b c Eitner, B. (1995). "Systematics of the Genus Alopias (Lamniformes: Alopiidae) with Evidence for the Existence of an Unrecognized Species". Copeia (American Society of Ichthyologists and Herpetologists) 1995 (3): 562–571.  
  4. ^ a b Sims, D.W., ed. (2008). Advances in Marine Biology, Volume 54. Academic Press. p. 175.  
  5. ^ Shimada, K. (2005). "Phylogeny of lamniform sharks (Chondrichthyes: Elasmobranchii) and the contribution of dental characters to lamniform systematics". Paleontological Research 9 (1): 55–72.  
  6. ^ "Family Alopiidae: Thresher Sharks – 3 species". ReefQuest Centre for Shark Research. Retrieved 2011-10-17. 
  7. ^ a b "Thresher Shark". 
  8. ^ Oliver SP, Turner JR, Gann K, Silvosa M and D'Urban Jackson T (2013) "Thresher sharks use tail-slaps as a hunting strategy" PLoS ONE, 8 (7): e67380. doi:10.1371/journal.pone.0067380
  9. ^ Dawkins, Richard (2004).  
  10. ^ "More oceanic sharks added to the IUCN Red List" (Press release).  

External links

  • FishBase entry on Alopiidae
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.