Thresher Shark Info

Thresher Shark Info

Thresher Shark Info

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

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 before been misidentified as the bigeye thresher. Thus far, it is only known from muscle samples and no aspect of its morphology has been documented.

Alopias pelagicus H. Nakamura, 1935 (pelagic thresher)
Alopias superciliosus R. T. Lowe, 1841 (bigeye thresher)
Alopias vulpinus (Bonnaterre, 1788) (common thresher)

Phylogeny and evolution

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.

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.

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

Named for and easily recognised by their exceptionally long, thresher-like tail or caudal fins (which can be as long as the total body length), thresher sharks are active predators; the tail is actually 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. 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. 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.

Behaviour

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 or oceanodromous habits. When hunting schooling fish, thresher sharks are known to “slap” the water, herding and stunning prey. The elongated tail is used to swat smaller fish, stunning them before feeding. Thresher sharks are one of the few shark species known to jump fully out of the water, making turns like dolphins, this behaviour 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. The 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.

Importance to humans

Threshers have a low fecundity, like all large sharks, and are highly vulnerable to overfishing. Besides being hunted for its 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.

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 managed in some areas for their value as both a recreational sport fish and commercial species.

Scientific classification   Kingdom: Animalia   Phylum: Chordata   Class: Chondrichthyes   Subclass: Elasmobranchii   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

Blue Shark Info

Blue Shark Info

blue shark info photo

The blue shark (Prionace glauca) is a species of requiem shark, family Carcharhinidae, that inhabits deep waters in the world’s temperate and tropical oceans. Preferring cooler waters,blue sharks migrate long distances, for example from New England to South America. Although generally lethargic, they can move very quickly. Blue sharks are viviparous and are noted for large litters of 25 to over 100 pups. They feed primarily on small fish and squid, although they can take larger prey. Blue sharks often school segregated by sex and size, and this behavior has led to their nickname “wolves of the sea”.

Blue sharks are light-bodied with long pectoral fins. The top of the body is deep blue, lighter on the sides, and the underside is white. It grows to 3.8 meters (12.5 ft) long and can weigh up to 204 kilograms (450 lb). The highest reported weight was 391 kilograms (860 lb) .

Reproduction

They are viviparous, with a yolk-sac placenta, delivering 4 to 135 pups per litter. The gestation period is between 9 and 12 months. Females mature at 5 to 6 years of age and males at 4 to 5. Courtship is believed to involve biting by the male, as mature specimens can be accurately sexed according to the presence or absence of bite scarring. Female blue sharks have adapted to the rigorous mating ritual by developing skin 3 times thicker than male skin.

Range and habitat

The blue shark is an oceanic and epipelagic shark found worldwide in deep temperate and tropical waters from the surface to about 350 meters. In temperate seas it may approach shore where it can be observed by divers, while in tropical waters it inhabits greater depths. It lives as far north as Norway and as far south as Chile. Blue sharks are found off the coasts of every continent, except Antarctica. Its greatest Pacific concentrations occur between 20° and 50° North but with strong seasonal fluctuations. In the tropics it spreads evenly between 20° N and 20° S. It prefers waters with a temperature range of 7–16 °C (45–61 °F) but will tolerate temperatures of 21 °C (70 °F) or above. Records from the Atlantic show a regular clockwise migration within the prevailing currents.

Feeding

Squid are important prey for blue sharks, but their diet includes other invertebrates such as cuttlefish and pelagic octopuses, as well as lobster, shrimp, crab, a large number of bony fishes, small sharks, mammalian carrion and occasional sea birds. Whale and porpoise blubber and meat have been retrieved from the stomachs of captured specimens and they are known to take cod from trawl nets. Blue sharks rarely eat tuna.

Predators

Adult blue sharks do not suffer predation on a regular basis, except by humans. Young and smaller individuals may get eaten by any sufficiently larger sharks such as the Great White Shark and the Tiger Shark . However, they are host to several species of parasites. For example, the blue shark is the definite host of the tetraphyllidean tapeworm, Pelichnibothrium speciosum (Prionacestus bipartitus). They become infected by eating intermediate hosts, probably Opah, (Lampris guttatus), and/or longnose lancetfish, (Alepisaurus ferox).

Relationship to humans

It is estimated that 10 to 20 million of these species are killed each year as a result of fishing. The flesh is edible, but not widely sought after; it is consumed fresh, dried, smoked and salted and diverted for fishmeal. The skin is used for leather, the fins for shark-fin soup and the liver for oil. Blue sharks are occasionally sought as game fish for their beauty and speed.   As of 2009 there have been 13 attacks on humans and 4 fatalities.

In captivity

Blue sharks, like most pelagic sharks, tend to fare poorly in captivity. Attempts at keeping them using circular tanks with long glide paths, and pools with 3 meters (9.8 ft) central depth gently ascending to zero depth have met with mixed results at best; most specimens last less than 30 days. As with other pelagic sharks, they seem to have trouble avoiding walls or other obstacles. In one case at Sea World San Diego, the Blue shark did fairly well until bull sharks were added to the tank; the Bull sharks ate the Blue shark. The captivity record for blue sharks as of 2008 was held by The New Jersey Aquarium for a specimen that lasted roughly 7 months before expiring of an apparent bacterial infection.

Scientific classification   Kingdom: Animalia   Phylum: Chordata   Class: Chondrichthyes   Subclass: Elasmobranchii   Order: Carcharhiniformes   Family: Carcharhinidae   Genus: Prionace   Species: P. glauca   Binomial name Prionace glauca

 

Mako Shark Info

Mako Shark Info

mako shark info photo

The shortfin mako shark (Isurus oxyrinchus—meaning “sharp nose”) is a large mackerel shark. It is commonly referred to as the mako shark together with the longfin mako shark (Isurus paucus).

In 1809, Constantine Rafinesque first described shortfin mako and coined the name Isurus oxyrinchus (Isurus means “the same tail”, oxyrinchus means “pointy snout”). “Mako” comes from the Māori language, meaning either the shark or a shark tooth. It may have originated in a dialectal variation as it is similar to the common words for shark in a number of Polynesian languages.

Range and habitat

The shortfin mako inhabits offshore temperate and tropical seas worldwide. The closely related longfin mako shark, Isurus paucus, is found in the Gulf Stream or warmer offshore waters.   It is a pelagic species that can be found from the surface down to depths of 150 m (490 ft), normally far from land though occasionally closer to shore, around islands or inlets. One of only four known endothermic sharks, it is seldom found in waters colder than 16 °C (61 °F).   In the western Atlantic it can be found from Argentina and the Gulf of Mexico to Browns Bank off of Nova Scotia. In Canadian waters these sharks are neither abundant nor rare. Swordfish are a good indication of shortfin makos as the former is a source of food and prefers similar environmental conditions.   Shortfin makos travel long distances to seek prey or mates. In December 1998, a female tagged off California was captured in the central Pacific by a Japanese research vessel, meaning this fish traveled over 1,725 miles (2,776 km). Another swam 1,322 miles (2,128 km) in 37 days, averaging 36 miles (58 km) a day.

The shortfin mako feeds mainly upon cephalopods, bony fishes including mackerels, tunas, bonitos, and swordfish, but it may also eat other sharks, porpoises, sea turtles, and seabirds. They hunt by lunging vertically up and tearing off chunks of their preys’ flanks and fins. Makos swim below their prey, so they can see what is above and have a high probability of reaching prey before it notices. Biting the caudal peduncle (near the tail) can immobilize the prey. In Ganzirri and Isola Lipari, Sicily, shortfin makos have been found with amputated swordfish bills impaled into their head and gills, suggesting that swordfish seriously injure and likely kill makos. In addition, this location, and the late spring and early summer timing, corresponding to the swordfish’s spawning cycle, suggests that these makos hunt while the swordfish are most vulnerable, typical of many predators.

Shortfin consume 3% of its weight each day and takes about 1.5–2 days to digest an average-sized meal. By comparison, an inactive species such as the sandbar shark consumes 0.6% of its weight a day and takes 3 to 4 days to digest it. An analysis of the stomach contents of 399 male and female mako sharks ranging from 67–328 centimetres (26–129 in) suggest makos from Cape Hatteras to the Grand Banks prefer bluefish, constituting 77.5% of the diet by volume. The average capacity of the stomach was 10% of the total weight. Shortfin makos consumed 4.3% to 14.5% of the available bluefish between Cape Hatteras and Georges Bank.

Shortfin over 3 metres (9.8 ft) have interior teeth considerably wider and flatter than smaller makos, which enables them to prey effectively upon dolphins, swordfish, and other sharks. An amateur videotape, taken in Pacific waters, shows a moribund spotted dolphin whose tail was almost completely severed, with a very large shortfin mako circling the dying dolphin. Makos also have the tendency to scavenge long-lined and netted fish.

Jaw

Its endothermic constitution partly accounts for its relatively great speed.

Like other lamnid sharks, the shortfin mako has a heat exchange circulatory system that allows the shark to be 7-10°F (4-7°C) warmer than the surrounding water. This system enables makos to maintain a stable, very high level of activity, giving it an advantage over its cold-blooded prey.   Behavior   The shortfin mako’s speed has been recorded at 50 kilometres per hour (31 mph) with bursts of up to 74 kilometres per hour (46 mph). They can leap approximate 9 metres (30 ft) high or higher in the air. Some scientists suggest that the shortfin mako can swim up to 100 kilometres per hour (62 mph), though scientists are still in debate over exactly how fast the shortfin mako shark can swim. This high-leaping fish is a highly sought-after game fish worldwide. There are cases when an angry mako jumped into a boat after having been hooked.   This shark is highly migratory.

Reproduction

The shortfin mako shark is a yolk-sac ovoviviparous shark, giving birth to live young. Developing embryos feed on unfertilized eggs in uterus during the 15 to 18 month gestation period. This is called (oophagy) (i.e. egg-eating). Shortfins do not engage in sibling cannibalism unlike the sand tiger shark (Carcharias taurus). The 4 to 18 surviving young are born live in the late winter and early spring at a length of about 70 centimetres (28 in). It is believed that females may rest for 18 months after birth before mating again. Last and Stevens (2009) report shortfin makos bear young on average every 3 years.   Lifespan   A landmark study by Natanson et al. (2006) has overturned previous highly inaccurate estimations of lifespan and sexual maturity in shortfin makos from the North Atlantic. Natanson et al. (2006) aged vertebrae of 258 specimens and recorded:  Maximum age of 29 years in males (260 cm FL)  Maximum age of 32 years in females (335 cm FL)  50% sexual maturity at 8 years in males (185 cm FL)  50% sexual maturity at 18 years in females (275 cm FL)   Last and Stevens (2009) report similar findings.

Captivity

Of all recorded attempts to keep pelagic shark species in captivity, the shortfin mako has fared the poorest; even more so than the oceanic whitetip shark, the blue shark and the great white shark. The current record is held by a specimen that, in 2001, was kept at the New Jersey Aquarium for only five days. Like past attempts at keeping Isurus in captivity, the animal appeared strong upon arrival but had trouble negotiating the walls of the aquarium, refused to feed, quickly weakened and died.[22]   Attacks on humans   ISAF statistics records forty-two shortfin attacks on humans between 1980 and 2010, three of which were fatal, along with twenty boat attacks.[23] Sharks can be attracted to spear fishermen carrying a stuck fish, and may slap them with cavitation bubbles from a swift tail flick. Generally these species of sharks will not attack humans; when humans are attacked, it is thought to be because they are mistaken for weakened or hurt prey.[citation needed]

 

Scientific classification   Kingdom: Animalia   Class: Chondrichthyes   Order: Lamniformes   Family: Lamnidae   Genus: Isurus   Species:   I. oxyrinchus

Binomial name Isurus oxyrinchus