Hammerhead sharks

 

The Life of Animals | Hammerhead sharks | The nine known species range from 0.9 to 6 m (3.0 to 20 ft) long and weigh from 500 to 1000 pounds. The positioning of the eyes, mounted on the sides of the shark's distinctive hammer head pointing outward like a Trex, give the shark good binocular vision, as well as 360-degree vision in the vertical plane, meaning They can see above and below Them at all times. The shape of the head was Previously thought to help the shark find food, aiding in close-quarters maneuverability and allowing sharp turning movement without losing stability.

From what is known about the Winghead shark, it would Appear That the shape of the hammer-head has to do with an evolved sensory function. Like all sharks, hammerheads have electroreceptory sensory ampullae of Lorenzini Called pores. By distributing the receptors over a Wider area, hammerheads can sweep for prey more effectively.These sharks have been Able to detect an electrical signal of half a billionth of a volt. In the evening, like other sharks, They Become solitary hunters.

Hammerheads are one of the Few Animals That acquire a tan from prolonged exposure to sunlight. Tanning Occurs a hammerhead is in shallow waters or close to the surface for long periods. Reproduction Occurs only once a year for hammerhead sharks and usually Occurs with the male biting the female shark shark violently until She agrees to mate with him The hammerhead sharks exhibit a viviparous mode of reproduction with females giving birth to live young. Like other sharks, fertilization is internal with the male transferring sperm to the female through one of two intromittent organs Called claspers.

When the supply of yolk is exhausted, the depleted yolk sac transforms into a structure analogous to a mammalian placenta (Called a "yolk sac placenta" or "pseudoplacenta"), through the which the mother delivers sustenance until birth. There is usually a litter of 12 to 15 pups; except for the which the Great Hammerhead births litters of 20 to 40 pups. The great and the scalloped hammerhead are listed on the World Conservation Union's (IUCN) 2008 Red List as endangered, whereas the smalleye hammerhead is listed as Vulnerable. Shark fins are prized as a delicacy, and overfishing is putting many hammerhead sharks at risk of extinction.

Horn shark

 

  

The Life of Animals | Horn shark | The horn shark inhabits the continental shelf of the eastern Pacific Ocean, occurring off the coasts of California and Baja California from Monterey Bay southward, and in the Gulf of California. Juvenile sharks horn the between 35-48 cm (1:15 to 1:57 ft) long prefer sandy flats with low vertical relief, in water 40-150 m (130-490 ft) deep. The relative abundances of the horn shark and the swellshark (Centroscyllim ventriosum), the which shares the same habitat, are negatively correlated, horn sharks Because favor water over 20 ° C (70 ° F) while swellsharks are more tolerant of cold. At Santa Catalina Island, a 20-year warming trend has resulted in an increase of population in the horn shark and a Decrease in the swellshark population. Horn sharks are less common than swellsharks in the northern Channel Islands, where the water is cooler.

Like other Bullhead sharks, the horn shark has a short, wide head with a blunt snout and prominent supraorbital ridges over the eyes. The horn shark's supraorbital ridges are low and terminate abruptly; the space the between Them on top of the head is Deeply concave. The inflow openings are encircled by a groove, while another groove connects the outflow openings to the mouth. There are 19-26 tooth rows in the upper jaw and 18-29 tooth rows in the lower jaw.

The fin spines of the reef-dwelling sharks are shorter than the horn Those living in algal habitats, as worn Become Their spines down on rocks from the sharks' movements. The first dorsal fin originates over the bases of the large pectoral fins, while the second dorsal fin originates slightly anterior to the free rear tips of the pelvic fins. The horn shark's dermal denticles are small and smooth, numbering some 200/cm2 on the back in adults The dorsal coloration consists of Various shades of gray or brown with many small dark spots, though these may be absent in older sharks; the Underside is Yellowish .

Under normal circumstances, the horn sharks are harmless to Humans and can readily be approached underwater. The horn shark has no commercial value in California, where it is unintentionally captured in traps and trawls and by recreational anglers. The shark's hardiness ensures That Often it can be returned to the water alive. This species benefits from the general restrictions placed on coastal fishing gear by the State of California. At present, the International Union for Conservation of Nature (IUCN) does not have sufficient information to assess the overall conservation status of this species; its status in United States waters is Likely Least Concern.

Spiny dogfish

  

The Life of Animals | Spiny dogfish | Spiny dogfish are fished for food in Europe, the United States, Canada, New Zealand and Chile. The fins and tails are processed into fin needles and are used in less expensive versions of shark fin soup in Chinese cuisine. In England this and other dogfish are sold in fish and chip shops as "rock salmon" or "shoo", in France it is sold as "small salmon" (saumonette) and in Belgium and Germany it is sold as "sea eel" ( zeepaling and Seeaal, respectively).

Once the most abundant shark species in the world, Populations of Squalus acanthias have Declined significantly. They are classified in the IUCN Red List of Threatened Species as Vulnerable globally and Critically Endangered in the Northeast Atlantic, meaning stocks around Europe have Decreased by at least 95%. In EU waters, a Total Allowable Catch (TAC) has been in place since 1999, but until 2007 it only applied to ICES Areas IIa and IV.

This drastic increase of led to the creation and implementation of many fisheries management policies Placing restrictions on the fishing of spiny dogfish. However, since the species is a late maturing fish, it takes a while to rebuild the population. In 2010, Greenpeace International has added the spiny dogfish to its seafood red list.

The current proposed quota for 2011 is 35.5m lbs. with a trip limit of 4000 lbs. In 2010, NOAA Announced the Eastern U.S. Atlantic spiny dogfish stocks to be Rebuilt in 2011 and concerns about predatory dogfish posing a serious threat to other stocks resulted in an emergency Amendment of the quota with Nearly 15 million pounds being added

Tiger shark

 

The Life of Animals | Tiger shark | The tiger shark is Often found close to the coast, Mainly in tropical and sub-tropical waters throughout the world. Along with the great white shark, Pacific sleeper shark, Greenland shark and sixgill sharks, tiger sharks are the largest extant Among sharks. It tends to stay in deep waters reefs That line, but it does move into channels to pursue prey in shallower waters. A number of tiger sharks can be seen at the Gulf of Mexico, North American beaches and parts of South America.

A recent study showed the average tiger shark That would be recorded at 350 meters (1,100 ft), making it uncommon to see tiger sharks in shallow water. However, tiger sharks in Hawaii have been observed in depths as shallow as 10ft and regularly observed in coastal waters at depths of 20 to 40-ft. The tiger shark is known as tababa in Kiribati and Tuvaluan. Tiger sharks have been observed feeding in the tidal passages of the between the lagoon and ocean in Tarawa, Kiribati. Spring tides bring in plankton or animalcule, the which attract small soft-shell crabs, sardines attract the which, the which attract the gray mullet, the which attract the blue-backed Trevally (rereba), the which then attract the tiger shark (tababa). The tiger shark is an apex predator and has a reputation for eating anything.

It commonly preys upon fish (teleosts), crustaceans, mollusks, dugongs, seabirds, marine seasnakes Mammals (eg bottlenose Dolphins, Spotted Dolphins), and sea turtles (eg green and loggerhead turtles). The broad, heavily calcified jaws and mouth Nearly terminal, combined with robust, serrated teeth, enable the tiger shark to take on these large prey. Due to high risk of predatory attacks, Dolphins Often avoid regions inhabited by tiger sharks. The tiger shark also eats other sharks (Such as sandbar sharks) and Will even eat conspecifics Tiger sharks may also attack injured or ailing whales and prey upon Them.

The tiger shark also scavenges on dead whales. Such in-one documented incident, They were the resource persons observed scavenging on a whale carcass alongside great white sharks, Carcharodon carcharias. The shark circles its prey and studies it by prodding it with its snout When attacking, the shark Often eats its prey whole. This shark typically reaches maturity at lengths of 2 to 3 m (6.6 to 9.8 ft) It is unknown how long tiger sharks live, but They can live longer than 12 years.

Whale shark

 

   
The Life of Animals | Whale shark | The whale shark inhabits all tropical and warm-temperate seas. The coral spawning of the area's Ningaloo Reef provides the whale shark with an abundant supply of plankton. Two small eyes are located Towards the front of the shark's wide, flat head. The shark has a pair each of dorsal fins and pectoral fins. Juveniles' tails have a larger upper than lower fin while the adult tail Becomes semi-lunate (crescent-shaped).

The whale shark is largest animal in the world outside of the large cetaceans. The average size of adult whale shark is estimated at 9.7 meters (31.82 ft) and 9 tonnes (20.000 lb). The largest verified specimen was caught on November 11, 1947, near Baba Island, in Karachi, Pakistan. It was 12.65 meters (41.50 ft) long, weighed more than 21.5 tonnes (47.000 lb), and had a girth of 7 meters (23.0 ft). Stories exist of vastly larger specimens quoted lengths of 18 meters (59 ft) are not uncommon in the popular shark literature, but no scientific records Their support for existence. In 1868 the Irish natural scientist Edward Perceval Wright obtained Several small whale shark specimens in the Seychelles, but claimed to have observed specimens in excess of 15 meters (49.2 ft), and Tells of reports of specimens surpassing 21 meters (68.9 ft).

The shark was too heavy to pull ashore, but Smith estimated That the shark was at least 17 meters (56 ft) long, and weighed approximately 37 tonnes (82.000 lb). A shark caught in 1994 off of Tainan County, southern Taiwan reportedly weighed 35.8 tonnes (79.000 lb). There have even been claims of whale sharks of up to 23 meters (75 ft). In 1934 a ship named the Maurguani CAME across a whale shark in the Southern Pacific Ocean, rammed it, and the shark consequently Became stuck on the prow of the ship, Supposedly with 4.6 meters (15.1 ft) on one side and 12.2 meters (40.0 ft) on the other. No reliable documentation exists for these claims and They Remain "fish-stories".

The eggs Remain in the body and the females give birth to live young the which are 40 to 60 centimetres (16 to 24 in.) long.  On March 7, 2009, Marine Scientists in the Philippines discovered what is believed to be the smallest living specimen of the whale shark.

Zebra shark

  

The Life of Animals | Zebra shark | The zebra shark Occurs in the tropical waters of the Indo-Pacific region, from South Africa to the Red Sea and the Persian Gulf (including Madagascar and the Maldives), to India and Southeast Asia (including Indonesia, the Philippines, and Palau), northward to Taiwan and Japan, Eastward to New Caledonia and Tonga, and southward to northern Australia. Adults and large juveniles frequent coral reefs, rubble, and sandy areas. There are unsubstantiated reports of this species from fresh water in the Philippines Zebra sharks Sometimes cross oceanic waters to reach isolated seamounts. Movements of up to 140 km (87 mi) have been recorded for shark However the individual, genetic data indicates there is little exchange That the between Populations of zebra sharks, even if Their ranges are contiguous The zebra shark has a cylindrical body with a large, slightly flattened head and a short, blunt snout.

The dorsal midline ridge merges into the first dorsal fin, placed about Halfway along the body and twice the size of the second dorsal fin. The pectoral fins are large and broad; the pelvic and anal fins are much larger but Smaller than the second dorsal fin.  The zebra shark attains a length of 2.5 m (8.2 ft), with an unsubstantiated record of 05.03 m (11.5 ft). Males and females are not dimorphic in size The color pattern in young sharks is dark brown above and light yellow below, with vertical yellow stripes and spots. As the shark grows to 50-90 cm (20-35 in) long, the dark areas begin to break up, changing the general pattern from light-on-dark stripes to dark-on-light spots.

The shark, a 1.9 m (6.2 ft) long mature female, was unusual in That albino animals rarely survive long in the wild due to Their lack of crypsis Zebra sharks are usually solitary, though aggregations of 20-50 individuals have been recorded off Southeast Queensland, aggregations of zebra sharks Several hundred forms every summer in shallow water.

There is an observation of an adult male zebra shark biting the pectoral fin of another adult male and pushing him against the sea floor; the second male was turned on his back, and remained motionless for Several hours. This behavior resembles the pre-copulatory behaviors the between male and female sharks, and in Both cases the biting and holding of the pectoral fin has been speculated to relate to one shark asserting dominance over the other.

Docile and slow-moving, zebra sharks are not dangerous to Humans and can be easily approached underwater. Many zebra sharks at dive sites have Become accustomed to the presence of Humans, taking food from divers' hands and allowing themselves to be Touched. The zebra shark adapts well to captivity and is displayed by a number of public aquaria around the world. Furthermore, the liver oil is used for vitamins, the fins for shark fin soup, and the offal for Fishmeal.