Thresher shark

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Thresher shark
Temporal range: 49–0  Ma [1]
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Thresher.jpg
Pelagic thresher (A. pelagicus)
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Lamniformes
Family: Alopiidae
Bonaparte, 1838
Genus: Alopias
Rafinesque, 1810
Type species
Alopias vulpinus
Bonnaterre, 1788
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 three extant species, all within the genus Alopias.

Contents

All three thresher shark species have been listed as vulnerable to extinction by the World Conservation Union since 2007 (IUCN). [2] All are popular sport fish.[ citation needed ] In addition, they are hunted for their meat, livers (for shark liver oil), skin (for leather), and fins for use in shark-fin soup.

Thresher shark jumping in Costa Rica Thresher shark jumping.jpg
Thresher shark jumping in Costa Rica

They do not appear to be a threat to humans.[ citation needed ]

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. [3] 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. [4]

Phylogeny and evolution

Megachasmidae

Alopiidae

A. vulpinus

undescribed Alopias sp.

A. superciliosus

A. pelagicus

Cetorhinidae

Lamnidae

Phylogeny of Alopiidae [4] [5]

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. [5] [6]

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. [4]

Distribution and habitat

Although occasionally sighted in shallow, inshore waters, thresher sharks are primarily pelagic; they prefer the open ocean, characteristically preferring water 500 metres (1,600 ft) and less.[ citation needed ] Common threshers tend to be more prevalent 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. A bigeye has also been found in the western Mediterranean, and so distribution may be wider than previously believed, or environmental factors may be forcing sharks to search for new territories. [7]

Anatomy and appearance

Small purple colored thresher caught at Pacifica Pier, California Pacifica thresher shark.jpg
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. [8] [9] 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. [10] 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 mass 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. [11] The three species can be roughly distinguished by the primary 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

The thresher shark mainly feeds on pelagic schooling fish such as bluefish, juvenile tuna, and mackerel, which they are known to follow into shallow waters, squid and cuttlefish. Crustaceans and occasionally seabirds are also taken. The thresher shark stuns its prey using its elongated tail as a weapon.

Behavior

External video
Nuvola apps kaboodle.svg Stunning tail: Thresher sharks evolved to slap and kill their preyNBC 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 "whip" the water. [11] The elongated tail is used to swat smaller fish, stunning them before feeding. Sometimes the thresher shark will slice the fish in half before eating. [12] Thresher sharks are one of the few shark species known to jump fully out of the water,using their elongated tail to propel them 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 (family Lamnidae) 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 feasting 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 first picture of a thresher shark giving birth was taken off the coast of the Philippines. [13]

Fisheries

Thresher sharks are classified as prized game fish in the United States and South Africa.[ citation needed ] Common thresher sharks are the target of a popular recreational fishery off Baja, Mexico.

Status

Because of their low fecundity, thresher sharks are highly vulnerable to overfishing.[ citation needed ] All three thresher shark species have been listed as vulnerable to extinction by the World Conservation Union since 2007 (IUCN). [2]

See also

Related Research Articles

Lamniformes order of fishes

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Shortfin mako shark the fastest living shark in the world

The shortfin mako shark, also known as the blue pointer or bonito shark, is a large mackerel shark. It is commonly referred to as the mako shark, as is the longfin mako shark. The shortfin mako can reach a size of 4 m (13 ft) in length. The species is classified as Endangered by the IUCN.

Atlantic mackerel Atlantic fish

The Atlantic mackerel, also known as Boston mackerel, Norwegian mackerel, Scottish mackerel or just mackerel, is a species of mackerel found in the temperate waters of the Mediterranean Sea, the Black Sea, and the northern Atlantic Ocean, where it is extremely common and occurs in huge shoals in the pelagic zone down to about 200 m (660 ft). It spends the warmer months close to shore and near the ocean surface, appearing along the coast in spring and departing with the arrival of colder weather in the fall and winter months. During the fall and winter, it migrates out into deeper and more southern water, seeking warmer temperatures.

Yellowfin tuna species of fish

The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.

Lamnidae family of fishes

The Lamnidae are the family of mackerel or white sharks. They are large, fast-swimming sharks, found in oceans worldwide. The name of the family is formed from the Greek word, lamna, which means fish of prey, and was derived from the Greek legendary creature, the Lamia.

Bigeye thresher species of shark

The bigeye thresher is a species of thresher shark, family Alopiidae, found in temperate and tropical oceans worldwide. Like other thresher sharks, nearly half its total length consists of the elongated upper lobe of the tail fin. Its common name comes from its enormous eyes, which are placed in keyhole-shaped sockets that allow them to be rotated upward. This species can also be distinguished by a pair of deep grooves on the top of its head, from which its scientific name is derived.

Common thresher species of shark (Alopias vulpinus)

The common thresher, also known as Atlantic thresher, big-eye thresher, is the largest species of thresher shark, family Alopiidae, reaching some 6 m (20 ft) in length. About half of its length consists of the elongated upper lobe of its caudal fin. With a streamlined body, short pointed snout, and modestly sized eyes, the common thresher resembles the pelagic thresher. It can be distinguished from the latter species by the white of its belly extending in a band over the bases of its pectoral fins. The common thresher is distributed worldwide in tropical and temperate waters, though it prefers cooler temperatures. It can be found both close to shore and in the open ocean, from the surface to a depth of 550 m (1,800 ft). It is seasonally migratory and spends summers at lower latitudes.

Longfin mako shark species of shark (Isurus paucus)

The longfin mako shark is a species of mackerel shark in the family Lamnidae, with a probable worldwide distribution in temperate and tropical waters. An uncommon species, it is typically lumped together under the name "mako" with its better-known relative, the shortfin mako shark. The longfin mako is a pelagic species found in moderately deep water, having been reported to a depth of 220 m (720 ft). Growing to a maximum length of 4.3 m (14 ft), the slimmer build and long, broad pectoral fins of this shark suggest that it is a slower and less active swimmer than the shortfin mako.

King-of-the-salmon species of fish

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Pelagic thresher species of shark (Alopias pelagicus)

The pelagic thresher is a species of thresher shark, family Alopiidae; this group of sharks is characterized by the greatly elongated upper lobes of their caudal fins. The pelagic thresher occurs in the tropical and subtropical waters of the Indian and Pacific Oceans, usually far from shore, but occasionally entering coastal habitats. It is often confused with the common thresher, even in professional publications, but can be distinguished by the dark, rather than white, color over the bases of its pectoral fins. The smallest of the three thresher species, the pelagic thresher typically measures 3 m (10 ft) long.

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References

  1. Bourdon, J. (April 2009). Fossil Genera: Alopias. The Life and Times of Long Dead Sharks. Retrieved on October 6, 2009.
  2. 1 2 "More oceanic sharks added to the IUCN Red List" (Press release). IUCN. 2007-02-22. Retrieved 2015-03-11.
  3. "fox shark - shark species". Encyclopædia Britannica.
  4. 1 2 3 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. doi:10.2307/1446753. JSTOR   1446753.
  5. 1 2 Sims, D.W., ed. (2008). Advances in Marine Biology, Volume 54. Academic Press. p. 175. ISBN   0-12-374351-6.
  6. Shimada, K. (2005). "Phylogeny of lamniform sharks (Chondrichthyes: Elasmobranchii) and the contribution of dental characters to lamniform systematics". Paleontological Research. 9 (1): 55–72. doi:10.2517/prpsj.9.55.
  7. Tsikliras, Athanassios C.; Oliver, Simon P.; Turner, John R.; Gann, Klemens; Silvosa, Medel; D'Urban Jackson, Tim (2013). "Thresher Sharks Use Tail-Slaps as a Hunting Strategy". PLoS ONE. 8 (7): e67380. Bibcode:2013PLoSO...867380O. doi:10.1371/journal.pone.0067380. ISSN   1932-6203. PMC   3707734 . PMID   23874415.
  8. https://www.youtube.com/watch?v=lHoCCPsRuhg
  9. "Family Alopiidae: Thresher Sharks – 3 species". ReefQuest Centre for Shark Research. Retrieved 2011-10-17.
  10. 1 2 "Thresher Shark".
  11. 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
  12. "Rare shark birth photographed for the first time". www.msn.com. Retrieved 7 April 2018.