Threats to Sharks

Because they are very slow to reach reproductive age, sharks have great difficulty recovering their populations after extreme depletions. Despite their superior physiology and hunting skills, many shark species are now threatened with extinction. Of the 465 assessed species of sharks living in our oceans, 74 are currently listed as threatened (including 11 species which are critically endangered) on the International Union for Conservation of Nature (IUCN) Red List. The IUCN has estimated that one quarter of all shark, ray, and chimaera species are threatened with extinction.

Sharks are unfortunately disappearing at an alarmingly fast rate due to several threats. In a study conducted by Oceana, researchers estimated that as many as 100 million sharks are still caught and killed worldwide due to bycatch, illegal fishing, and the demand for shark fins. This makes it extremely difficult for endangered sharks to survive.

BYCATCH

Bycatch is the accidental capture of non-target fish and other marine life, and occurs in fisheries around the world. When lines are unattended, such as in some longline fisheries, the toll can be particularly high. The species that are most at risk include dusky sharks and scalloped hammerheads. Dusky shark populations off the Atlantic coast has declined by 85 percent. Scalloped hammerheads are extremely susceptible to fishing mortality due to their uniquely shaped and sensitive bodies.

ILLEGAL FISHING

Oceana reports that up to 24 countries may be catching sharks within the Atlantic and Mediterranean Sea without reporting such catches. Commercially-caught species like mako and blue sharks are fished without any restrictions.

SHARK FIN DEMAND

The international fin trade is one of the greatest threats to shark species. It is a wasteful and harmful practice in which only two to five percent of the shark is even used — once a shark's fins are cut off at sea, the shark is tossed back into the water to drown.

RECREATIONAL FISHING

The impact of commercial fishing on shark populations is astonishing. Recreational fishing for sharks is popular in many places and species targeted are blue sharks, shortfin mako, porbeagle, and thresher sharks.

HABITAT LOSS, POLLUTION AND ENVIRONMENTAL DEGRADATION

Coastal development has increased significantly which has altered habitats, increased levels of pollution and resulted in the general environmental degradation. Many shark species use inshore coastal and estuarine habitats as a safe place for finding food, giving birth and growing up away from predators and competitors. Thus, they are vulnerable to negative changes in their habitat.

Sharks are susceptible to pollution (filtered from land activities or directly deposited into the seas) and environmental contamination. As apex predators with very slow growth, they accumulate the pollutants and toxins in the environment and bioaccumulating all the toxins of their prey.

REFERENCES

http://www.defenders.org/sharks/threatshttp://shark-facts.com/
http://oceana.org/blog/what-are-some-biggest-threats-facing-sharks
http://www.sharksavers.org/en/education/sharks-are-in-trouble/other-threats-facing-sharks/

Great White Shark

Source: Kids Konnect

Other names for this lethal predator include: White Death, Great Pointer or White shark.

Kingdom          Animalia

Phylum            Chordata

Class                Chondrichthyes

Subclass           Elasmobranchii

Superorder       Selachimorpha

Order                Lamniformes

Scientific Name Carcharodon Carcharias

Type                Fish

ANATOMY

Source: NSW Government

It is well-known for its size, reaching upwards of 6.4m (21 ft) in length. Females are larger than males. Their weight limit is approximately 3,000 kg (7,000 lb). It is the fourth largest shark, following the megamouth shark, the basking shark and the whale shark.

It's famous for its dark to light grey upper body and all white lower half. To a seal swimming on the surface, the shark would resemble the murky depths below it and if seen from below, the stark white belly would resemble the light from above, known as countershading.

Source: Mirror UK

It has a long pointed conical snout, similarly sized upper and lower lobes of the tail and a mouth filled with serrated teeth. The jaws of the sharks are lined with rows of teeth just beneath the gum. It is composed of nearly pure muscle, with very little fat. It stores fat in the liver for emergency use or for travelling long distances without eating.

BEHAVIOUR

The Great White’s behaviour is not well known. But some have been found to have bites matching other Great Whites, suggesting that a proximity warning is given with a light bite. Spy hopping is frequently done as the shark breaks the surface of the water and looks above the ocean for prey. Research suggest that it has to do with smelling for prey, as smell travels faster through air than water.

They also breach whereby they, usually while attacking, charge from below the prey at up to 40kmph (25mph). This results in huge sharks breaking the surface of the water while grabbing the prey, flying up to 3 m (10 ft), above the water.

 

Source: The Animal Globe

DIET

They are carnivorous, preying on nearly any fish in the ocean, but preferably fat rich animals. Juvenile (younger than 15) sharks hunt and eat small fish because the cartilage in their jaws isn’t mineralized to withstand the force for a stronger bite. Older sharks are able to hunt larger prey, such as elephant seals, sunfish and even whales. They also scavenge food, consuming off the dead carcasses of, for example, whales. This particular species is warm-blooded and although it doesn’t keep a constant body temperature, it needs to eat a lot of meat to regulate its temperature. 

HABITAT & DISTRIBUTION

Their distribution is widespread, found in every ocean and sea across the world. They are commonly found as far north as the Upper Atlantic and Pacific, just south of Arctic waters and as far south as the southern tip of Australia. The Great White is considered native to the Mediterranean states, United States, sub-Saharan coastal states, South America and the Australian states. They stay close to coastal shelves, preferring to hunt off the coastline. They spend their time in temperate waters all over the world, but have made fleeting trips into colder water in the north.



Source: Animal Fact Guide

REPRODUCTION

Sharks reach reproductive maturity at 15 years. Females are ovoviviparous (they hatch their eggs internally then give birth once their pups are strong enough). Pups are oophagous (they eat the weaker eggs while gestating). After mating the female develops several eggs which hatch in her womb. They give birth between spring and summer and have specific breeding grounds. They have anywhere between 1-5 pups. Pups are roughly 1 ft. long when they are born and weigh around 5kg. Their jaws are strong enough to kill within their first month of life.

CONSERVATION STATUS

Their numbers have steadily declined, though there is no exact number of population size. According to the International Union for the Conservation of Nature, their status is currently Vulnerable but it is on the cusp of being labelled endangered due to overfishing.



Source: HD Desktop Wallpapers

REFERENCES

http://www.animalfactguide.com/animal-facts/great-white-shark/

http://www.defenders.org/sharks/threatshttp://shark-facts.com/

http://www.kidzone.ws/sharks/facts.htm

http://www.kidzone.ws/sharks/facts.htm

http://www.sciencekids.co.nz/sciencefacts/animals/shark.html

http://shark-facts.com/great-white/

Shoutout to SHARKS

INTRODUCTION


Source: Shark Facts

It is indisputable that sharks are some of the most majestic creature of the marine world. Sharks are an apex predator and they are at the top of the marine food chain and, consequently, regulate species populations that are below them. Sharks have been around for 400 million years (pre-dating dinosaurs and even trees). Their Conservation Status is Threatened. Frequently there is a misconception about them. Although they still remain dangerous species, attacks on humans are more commonly rare and they are far more scared of than we could ever be of them. There are more than 465 known species of sharks in our oceans. More worrisome is the fact that shark populations have declined considerably and has cascading effects throughout the ocean’s ecosystems. In fact, they are amongst the most threatened marine vertebrates on Earth, with some species facing extinction as they face numerous human threats.

Kingdom                      Animalia

Phylum                        Chordata

Class                            Chondrichthyes

Subclass                       Elasmobranchii

Scientific Name           Selachimorpha

Type                             Fish

ANATOMY

Source: Wikipedia

It features include a torpedo-like body shape, large distinctive dorsal fin and gaping tooth filled jaws. They are highly sophisticated. Their general anatomy is fairly consistent in all the various species.

Sharks boast five to seven gill slits on the sides of the head, unlike most fish that only have one gill. They rely on a large oil filled liver for buoyancy and takes up around 30% of their total body mass, using it in conjunction with forward movement to control vertical position.

Skeleton
Chondrichthyes have skeletons made up of cartilage rather than bone, and lack a swim bladder. Cartilage is lighter, more durable, and flexible than bone, contributing to their overall agility whilst also saving energy. This is vital when sharks must constantly move to prevent sinking.

Jaws
Sharks have powerful jaws. The jaws of sharks are not attached to their skull. It moves separately with independent upper and lower jaws, allowing them to lift their head and thrust their mouth forward to bite its prey. The surface of shark’s jaws have extra support in the form of tiny hexagonal plates called ‘tesserae’ – calcium salt deposits which give shark cartilage more strength.

Source: Kidzone

Teeth

Their teeth are sharp and pointy. Sharks may have up to 3,000 teeth at one time and are fully embedded into the gums. A shark bites with its lower jaw first and then its upper.  Each type of shark has a different shaped tooth depending on their diet. Interestingly, sharks never run out of teeth – they continuously grow multiple rows of replacement teeth in a groove inside of the jaw, and are usually replaced one at a time as opposed to entire rows. It is estimated that some sharks may lose 30,000 or more teeth in their lifetime, with replacement rates varying from several days to several months.

The shape and size of the teeth vary depending on their purpose. There are four main types of shark teeth:
·         Needle-like teeth are found in sharks whose diet consist of small to medium sized fish and are effective at gripping onto agile and slippery fish.
·         Serrated, wedge like teeth are found in larger species that feed on larger prey. It is effective at cutting off chunks of flesh for easy swallowing.
·         Teeth which serve no purpose are found in plankton feeders (for example the basking and whale shark who uses their gills to filter feed).
·         Dense, plate like teeth are used to crush the shells of prey (for example bivalves and crustaceans). Includes smaller sharks like nurse or angel sharks.

Fins and Tails
The majority of sharks have 8 rigid fins:
◾A pair of pectoral fins that lift the shark as it swims
◾One or two dorsal fins offering stability
◾A pair of pelvic fins offering stability
◾An anal fin offers stability
◾A caudal fin (tail) that propels the shark forward

The shark’s tail provides its forward motion, with speed and acceleration dependent on shape and size. Some tails have large upper lobes for slow cruising with short and sudden bursts of speed, whereas others have larger lower lobes for continued pace.

Skin
Their skin is made of denticles and not from ordinary fish scales and act as an outer skeleton for easy movement and for saving energy in the water. It is constructed like hard, sharp teeth and help to protect the shark from injury. Sharks wounds heal quickly.

The upper side of a shark is normally dark to blend in with the water from above and their undersides are white or lighter coloured to blend in with the lighter surface of the sea from below which helps to camouflage them from predators and prey.

SIZE
Their size vary from 17cm (Spined Pygmy Shark) to 12 metres (Whale Shark).

DIET
Most shark species are carnivorous. The range of prey is exceptionally broad, including small bivalves, crustaceans, plankton, krill, marine mammals, and even other sharks (for example, a tiger shark might eat a bull shark, a bull shark might eat a blacktip shark and a blacktip shark might eat a dogfish shark). Generally sharks eat live prey, but have been known to feed on large whale carcasses. Sharks also have a very acute sense of smell that allows them to detect blood in the water from miles away. The gentle giants (for example the whale and basking shark) feed on plankton, filtering the water and trapping small organisms with sieve-like filaments. Sharks eat normally alone, but sometimes one feeding shark attracts others and all begin to try to get a piece of the prey. Some shark species attack and surprise their prey (such as seals and sea lions) from below.

HABITAT

Source: Animal Fact Guide

Sharks occur in all seas and have adapted to living in a wide range of aquatic habitats and varying temperatures. Some species inhabit shallow, coastal regions, others live in deep waters, on the ocean floor and in the open ocean. They mostly avoid fresh water. An exception is the bull and river sharks that swim between sea and fresh water. They are normally found to a depth of 2,000 meters, with some existing even deeper. ‘Pelagic’ sharks (for example the Great White) prefer large open waters. ‘Benthic’ sharks (including the wobbegong) are seen skating along the ocean floor. Typically, sharks are confined to their suited habitat for their whole lives. But some migrate short distances or entire oceans for feeding or breeding purposes.

BEHAVIOUR
Only a few species are solitary hunters (including the great white) but, they too, often coexist at active hunting or breeding grounds. Most execute a range of social behaviour, hunting in packs or congregating in large numbers. Sharks characteristically cruise at an average speed of 8km per hour because they need to move in order to breathe. This forces water over their gills, delivering oxygen to the blood stream. Conversely, some shark species have adapted to benthic living, resting on the sea bed, and pumping water over their gills. Interestingly, they never enter a true state of sleep. Their eyes remain open and even track the movements of their surroundings during periods of inactivity. Some species are even able to ‘sleep swim’ by being unconscious while meandering around the ocean as a result of swimming being coordinated by their spinal cord and not their brain. Most sharks are particularly active at night when they hunt. Some shark species are solitary, while others display social behaviour. For example, hammerhead sharks school during mating season around seamounts and islands.

SENSES

Source: Animal Fact Guide

Sharks have excellent senses. Two-thirds of a shark's brain is dedicated to its smell sense. They are able to detect a drop of blood from very far away and it gives them the ability to determine the direction of a particular scent based on the time it takes to reach one nostril compared to the other. Their nostrils are primarily used for smelling (as opposed to breathing) and are located on the underside of their snout.

Furthermore, they have great eyesight. New research shows that sharks may be colour-blind. A mirror like layer in the back of the eye called the tapetum lucidum doubles the intensity of incoming light and allowing them to see remarkably well in dim conditions. They don’t blink, even though they have eyelids. They rely on surrounding water to clean their eyes. When hunting or being attacked, some sharks have tough membranes that slides over and protects the eyes. Species that don’t have this membrane, roll their eyes backwards when striking prey.

Sharks do have ears which are located within a small opening on each side of their head, but it isn’t visibly present. Sound travels faster in water and sharks rely on it to alert them to prey or danger which can detected from over 800 feet away.

They are able to feel vibrations in the water using a line of canals that go from its head to its tail and are filled with water and contain sensory cells with hairs growing out of them. These hairs move when the water vibrates and alerts it to potential prey. Sharks also have a sensory organ called the "ampullae of Lorenzini" which they use to "feel" the electrical field coming from its prey.

REPRODUCTION
Sharks mostly live 20-30 years. They mature slowly and reach a reproductive age from 12 to 15 years. Sharks are a k-selected species (they produce a small number of larger, more developed young), resulting in a relatively high survival rate. Nevertheless, mating between sharks is still rarely observed, especially between the larger species such as the great white. Many species only give birth to one or two pups at a time and have difficulty recovering after their populations have declined.
 There are also different ways that sharks come into this world, including: eggs are laid (like birds); eggs hatch inside the mother and then are born; and pups sharks grow inside the mother (like humans).
 

Source: Arkive

Baby sharks are called pups. Shark pups are born with fully-fledged sets of teeth. Sharks don’t care for their babies after they are born, but they do search for a safe place where they can lay their eggs or give birth. Soon after birth, they swim away to feed and live on their own.

POPULATION
It is problematic to estimate population numbers since there are many dissimilar species spanning a large geographic area. But it is undeniable that overall shark numbers are on the decline due to several threats they face in the wild. Their lifespan is about 20-30 Years in the wild.

REFERENCES
http://animals.howstuffworks.com/fish/sharks/shark6.htm

http://www.animalfactguide.com/animal-facts/great-white-shark/

http://www.defenders.org/sharks/basic-facts

http://www.defenders.org/sharks/threatshttp://shark-facts.com/

http://www.kidzone.ws/sharks/facts.htm

http://www.kidzone.ws/sharks/facts.htm

http://www.kidzworld.com/article/27222-shark-fun-facts

http://oceana.org/blog/what-are-some-biggest-threats-facing-sharks

http://www.sciencekids.co.nz/sciencefacts/animals/shark.html

http://shark-facts.com/great-white/

http://shark-facts.com/hammerhead-shark-facts/

http://www.sharksavers.org/en/education/sharks-are-in-trouble/other-threats-facing-sharks/