Shark of the month: Great Hammerhead Shark

1024px-Sphyrna_mokarran_camden

Anatomy and Appearance

Great hammerheads have an unmistakeable identity with the hammer shaped head that derives its name and the very large first dorsal fin that is strongly falcate. The second dorsal fin is also large but not as large as the first and has a strongly concave rear margin. They are a dark brown or olive colour dorsally and this fades into white ventrally. Juveniles are around 60-70cm when they are born and adults can grow to around 6 metres, although most grow to around 3-4 metres.

image source: animalsearths.blogspot.com

image source: animalsearths.blogspot.com

Reproduction

Female reach Hammerheads reach maturity at around 2 metres with males growing a little larger at 2.5 metres before reaching maturity. The gestation period is 11 months for the great hammerhead and during this time eggs are nourished by a yolk-sac placenta. Then, during the spring and summer months parturition occurs with litters of somewhere between 6-40 pups. Unlike a lot of shark species, great hammerheads mate routinely throughout the water column and have even been known to mate at the surface.

Habitat and Distribution

The great hammerhead shark is found throughout the Atlantic, indian and pacific oceans and also in the Mediterranean sea. The great hammerhead is predominately a costal shark that is found over continental shelves and in lagoons. They do mirgrate seasonally, in the summer months they head towards the poles in search of colder water and during the winter they will head back towards the equator in search of warmer water. They have been found to inhabit water from a depth range of 1 metre all the way down to around 80 metres.

hammerhead-distribution-940px-Sphyrnidae_distribution_map.svg

Diet

Great hammerheads are an opportunistic predator. They feed on a wide range of prey from invertebrates like crabs, lobsters, octopus and squid and bony fish such as groupers, catfish, tarpons, sardines and porcupine fish. However the favourite prey of the great hammerhead are rays and skates especially stingrays. Interestingly hammerheads seem to be unaffected by the stings of rays and catfish and they are commonly found with spines sticking out of their skin and jaws. They have also been known to prey on other sharks and being opportunistic have been known to attack grey reef sharks when they are exhausted from pursuing mates.

Image source: dailymail.co.uk

Image source: dailymail.co.uk

Conservation Status

endangeredGreat hammerhead sharks are very vulnerable to overfishing and are a target species in many forms of fishing from long line, hook and line, fixed bottom net, pelagic, and bottom trawl fisheries. Even if they are not a target species they are often caught as by catch. As with many shark species the fins are very valuable and used in shark fin soup. The skin of the sharks can also be used for leather production and its liver for its rich vitamin oils. It is endangered in the North West Atlantic and in the gulf of Mexico. It is also endangered in the South West Indian ocean. Along the west coast of Africa it is critically endangered with an estimated 80% decline in the past 25 years.

Much thanks to Chris Facey who wrote this article.

Saw Shark – Shark of the month

sharsk-ahoy-tumblr_lrdwlg1QaU1qj1xawo1_500

Photo: Tumblr

The saw shark is one of the weirdest ocean floor sharks. There are two genera of this fascinating shark family, the Pristiophorus with five gill slits on each body side, and the Pliotrema, that have six. There are a total of six species. Sawsharks can range up to 5.6 ft (1.7 m) in length and weight up to 18.7 lbs, with females usually slightly larger than the males.

Anatomy

Sawsharks have two dorsal fins, but lack anal fins. They can live as a solitary creature, or be a part of a group. The body of a saw shark is covered with placoid scales (called dermal denticles) with pointed tops. They have yellowish-brown skin, covered with dark blotches and spots. Skin coloration provides camouflage and helps them blend with sandy bottoms.

Saw Shark Diet

dutchsharksociety.org-korotkonos_pilonos

Saw sharks typically feed on fish, squid, and crustaceans, depending on species. Sawsharks stir up the seabed with their long, toothed snout, feeling for prey with their barbels, and the help of their electro-receptors (ampullae of Lorenzini) on the underside of the saw and then taken into the small mouth.  They use their serrated snout to kill the prey, with fast movement of the snout from side to side cuts the prey into fine chops that can be swallowed easily. The teeth of their saw typically alternates between large and small, and their long, flat snout bears about 25-45 serrated teeth on either side. (Photo: Dutch Shark Society)

Saw Sharks vs Sawfishes

Saw sharks and sawfishes are cartilaginous fishes possessing large saws. However, sawfishes are not sharks, but a type of ray.  The gill slits of the sawfishes are positioned on the underside (like a ray), but the gill slits of the saw shark are positioned on the side (as with sharks). Another clear difference is that a sawfish has no barbels and a saw shark has a prominent pair halfway along the saw. The barbels look like a thin mustache of sorts and act as a kind of antennae, feeling the way along the ocean bottom until it finds some prey of interest. Sawfishes have a much larger maximum size, lack barbels and have evenly sized teeth rather than alternating saw teeth.

sawshark-vs-sawfish

Saw Shark Distribution and Habitat

Saw sharks can be found in temperate waters from South Africa to Australia and Japan, at depths of 40 m (130 ft) and below, however in 1960, the Bahamas sawshark was discovered in the deeper waters (640 m to 915 m) of the northwestern Caribbean.  Saw shark can survive more than 15 years in the wild.

Saw Shark Reproduction

dutchsharksociety.org-Embryo_Mike-ParryMating season of saw sharks takes place seasonally in the coastal areas and females mate once every two years. Saw sharks are ovoviviparous, with litters of 7 to 17 pups and a gestation period of 12 months. Young saw sharks are born with folded teeth to prevent serious injuries of mother during the birth. They are born fully developed and look like miniature version of adults. Saw sharks take care of their young until they become sexually mature (at the age of 2 years) and able to fend for themselves. (Photo: Dutch Shark Society)

Saw Shark Conservation Status

www.pbs.org-lalongnose

Photo: Tumblr

These interesting creatures are often killed because of their meat. The number of saw sharks has declined in the past couple of decades due to commercial fishing, but they are still not on the list of endangered species.

This species is harmless to people. It has little importance to fisheries, except in Japan where its meat is considered to be high-quality and it is sought for human consumption. Like many sharks, the sawshark is captured accidentally as “Bycatch” in many fisheries.
The International Union for Conservation of Nature Red List categorizes the Japanese Sawshark as “Data Deficient” because it is uncommon across its range, and so little information is available about its populations.

sawfish-concern

Thanks to Rose Nomura (Shark Guardian volunteer) for writing this blog!

Sources
http://www.softschools.com/facts/animals/saw_shark_facts/477/
https://www.tumblr.com/search/sawshark
http://www.dutchsharksociety.org/ever-saw-a-sawshark/
http://www.sharksider.com/japanese-sawshark.html

Cookiecutter Shark – Shark of the Month

Image source: australianmuseum.net.au

Image source: australianmuseum.net.au

The cookiecutter shark, also commonly known as the cigar shark, is a small dogfish shark that prefers warm oceanic waters, usually near islands. This shark prefers deep water and has been recorded in waters as deep as 3.7 km. It is a diurnal shark, meaning that it makes a nightly migration to the surface and then descends back down during the day. Due to their habitat, these sharks are rarely encountered and only a few attacks on humans have ever been documented, and therefore, is not considered to be highly dangerous.

Cookiecutter Shark Anatomy & Appearance

The cookiecutter shark is a small shark that has a long, cigar-shaped body with a rounded snout. At full maturity, it reaches a maximum length of 42 cm (17 in) for males and 56 cm (22 in) for females. It has large, green, oval eyes that are placed forward on its head. Behind its eyes are large spiracles, which lead to its respiratory systems to enable them to breath. The mouth is short and it is filled by 30-37 rows of teeth in the upper jaw and 25-31 rows of teeth in the lower jaw. The teeth in the upper jaw are narrow, small, straight, and have a smooth-edged cusp. The lower teeth are larger, wider, and serrated, while the bases of the teeth are locked together to create a saw-like edge. The pectoral fins are short and are four-sided. The two dorsal fins are placed near the end of the body. The second dorsal fin is a little bit larger than the first one. The pelvic fin is the largest of the fins on the body. There is no anal fin. The caudal fin is wide with no visible ventral notch. The body is a dark brown color with lighter counter shading on the underside.

image source: en.wikipedia.org

image source: en.wikipedia.org

Cookiecutter Shark Range & Habitat

The cookiecutter shark inhabits all tropic and sub-tropical oceans and is most commonly found between the latitudes of 20°N and 20°S. It prefers warm water temperatures between 18-26°C (64-79°F). In the Atlantic, it has been documented to be in the Bahamas, southern Brazil, Sierra Leone, southern Angola, Cape Verde, Guinea, and South Africa. In the Indo-Pacific, it has been documented in Mauritius, New Guinea, Australia, Japan, and New Zealand. In the Pacific, it has been documented in Fiji, Hawaiian Islands, Galapagos, and Guadalupe Islands.

The cookiecutter shark is known to migrate diurnally, meaning that it migrates from the deep ocean to the upper water column at night. It spends the day at a depth of 1-3.5 km and migrates up to around 85 meters at night, and occasionally all the way up to the surface. It is most commonly found near islands, perhaps for reproductive and predatory reasons.

Isistius_brasiliensis_distmap

Feeding

Cookiecutter sharks prey on virtually all medium to large sized animals as they take round, cookiecutter like bites out of the sides of animals. Bite scars have been found on cetaceans, pinnipeds, dugongs, sharks, deepwater stingrays, and bony fish. They also hunt and eat entire squids that are 15-30 cm in length, which is around the same size as the shark itself.

Image source: listnation.blogspot.com

Image source: listnation.blogspot.com

en.wikipedia.org-Cookiecutter_damage

Image source: en.wikipedia.org

An attack from a cookiecutter shark will leave a round, crater-like wound that is an average of 5 cm across and 7 cm deep. Diseased or weakened animals seem to be more susceptible to bites, but in some places, healthy animals readily bear the scars from cookiecutter sharks.

The shark feeds by first securing itself to the body surface of its intended prey by closing it spiracles, retracting its tongue, and suctioning its lips in order to create negative pressure to secure a seal. Then, it bites using its narrow upper row of teeth to anchor itself and its bottom teeth to “saw” into the prey. The shark then rotates its body to cut a complete circle out of the animal.

Conservation and Importance

The International Union for Conservation of Nature (IUCN) has listed the cookiecutter shark under the category of Least Concern. This is due to the fast that these sharks are widely distributed, they have no commercial value, and they are not very susceptible to fisheries.

Special thanks to Paige Henderson for writing this article.

Angel Shark – Shark of the Month

Angel Shark Project Carlos Suarez, Oceanos de Fuego

Photo credit: Carlos Suarez, Oceanos de Fuego

The angel shark (Squatina squatina) is one of the more unique sharks with its exceptionally flat body and large pectoral fins. It is certainly one of the many favorite sharks that we discuss during our Shark Guardian presentations. And everyone loves a shark that is shaped like an angel, which is how it got its name. Incredibly there are 23 different species of angel sharks!

It seems to resemble more of a ray, than a shark. Its skin is usually  grey to reddish or greenish-brown, scattered with small white spots and blackish dots. Young angel sharks may also have white net-like markings and large, dark blotches, and become more plain as they grow older.  They are masters of disguise and bury themselves in sand or mud waiting for prey, which includes fish, crustaceans, and various types of mollusks.  Don’t be fooled by their grace, their pretty face quickly transforms with its extensible jaws that rapidly snap upward to capture prey with their long, needle-like teeth!

Angel sharks possess simple, whisker-like projections near the nostrils (nasal barbels), which are used to taste and feel and they have large, round eyes with vertical slit pupils. It has no anal fin, and unusually for sharks, the lower lobe of the caudal fin is longer than the upper lobe. Most types grow to a length of 1.5 m (5 ft), with the Japanese angel shark, Squatina japonica, known to reach 2 m.

This video below shows how the angel shark attempts to prey on a horn shark. However, the horn shark got its name for having a special secret weapon against larger predators like the angel shark. A must watch!

 

Angel Shark Distribution & Habitat

Angel Shark found on en.wikipedia.org

Image source: en.wikipedia.org

Angel sharks occur worldwide in temperate and tropical seas. Most species inhabit shallow temperate or tropical seas, but one species inhabits deeper water, down to 1,300 m (4,300 ft).   They are nocturnal and can be found swimming around up off the bottom at night. In the daytime it lies buried in the mud or the sandy bottom, with little more than its eyes protruding.  In the northern parts of its range the Angel Shark is seasonally migratory, and makes northwards journeys during the summer.

 

Angel Shark Population

Image source: elasmodiver.com

Angel sharks were once a common and important bottom dwelling predator over large areas of coastal and sediment habitat in the Northeast Atlantic, Mediterranean and Black Seas. Due to aggressive fishing methods suck as trawling, set nets and longlines, Angel Sharks are highly vulnerable from birth onwards and population has decreased dramatically during the past 50 years. This has resulted in the sad fact that Angel sharks have been declared extinct in the North Sea and they are nearly non-existent in large areas of the northern Mediterranean. Angel sharks are now extremely uncommon throughout most of the remainder of its range, with the possible exception of some areas of the southern Mediterranean and Canary Islands where its status needs to be confirmed and conservation measures introduced as a matter of urgency. Rate of population increase, longevity and mortality are unknown.

bycatch

For more information about the bycatch issue, check out this great infographic here.

Angel Shark Reproduction

Felipe Ravina Olivares-felip

Photo credit: Angel Shark Project

Angel Sharks are ovoviviparous, with both ovaries functional. It has moderate-sized litters of 7 to 25 young, which vary according to the size of the female. Records of size at birth are 24 to 30 cm. Gestation period is 8 to 10 months, born in December to February in the Mediterranean but later in northern parts of its range (July in England). Age at maturity, reproductive age and periodicity are unknown. Females reach maturity at 128 to 169 cm, and males at 80 to 132 cm, with maximum sizes of 183 cm and possibly up to 244 cm, with estimates of less than 240 cm in the Mediterranean Sea.

Conservation Status

Angel Shark by Carlos Suarez, Oceanos de Fuego

Photo Credit: Carlos Suarez

Historic data shows a dramatic decline in angelsharks from tuna traps operating in the Northern Tyrrhenian Sea with catches of the genus Squatina reported at an average of 134 specimens from 1898 to 1905, down to 15 between 1914 and 1922. This early decline probably marks the beginning of trawling activity in the area, to which Angel Sharks are highly susceptible. A low rate of exchange between Squatina populations may makes them especially prone to local depletion and means that recolonisation will be extremely low.  Habitation degradation from humans and tourism are also possible threats.

By 1985, the annual take of angel shark on the central California coast had increased to more than 454 metric tons or an estimated 90,000 sharks. The population declined dramatically and is now regulated. In April 2008, the UK government afforded the angel shark full protection under the Wildlife and Countryside Act. Once considered abundant in the Atlantic Ocean, the angel was classified as “critically endangered” in 2010.

There is an urgent need to confirm the status of this species in the southern Mediterranean, Canary Islands and other areas where populations may still persist. This is why projects like The Angel Shark Project are so important. This project aims to provide vital information on the ecology and distribution of this shark in the Canary Islands, that may be used to implement rapid conservation measures.

angel-shark-concern

Written by Rose Nomura (Shark Guardian Volunteer)

Sources:
http://en.wikipedia.org/wiki/Angel_shark

http://www.iucnredlist.org/details/39332/0
http://www.arkive.org/angel-shark/squatina-squatina/image-G124005.html

Whale Shark – Shark of the month

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The whale shark (Rhincodon typus) is a slow-moving filter feeding shark and the largest known shark species. The largest confirmed individual had a length of 12.65 m (41.50 ft) and a weight of more than 21.5 metric tons. Unconfirmed reports of considerably larger whale sharks exist. Claims of individuals over 14 m long and weighing at least 30 metric tons are not uncommon. The whale shark holds many records for sheer size in the animal kingdom, rivalling many of the largest dinosaurs in weight. There is only 1 species of whale shark that originated about 60 million years ago.

Whale Shark Distribution and Habitat

800px-Cypron-Range_Rhincodon_typus.svgThe whale shark inhabits all tropical and warm-temperate seas as a pelagic shark. Although typically seen offshore, it has been found closer to land, entering lagoons or coral atolls, and near the mouths of estuaries and rivers. Its range is generally restricted to about 30° latitude. It is capable of diving to depths of at least 1,286 m and is migratory. On 7 February 2012, a large whale shark was found floating 150 kilometers off the coast of Karachi, Pakistan. The length of the specimen was said to be between 11 and 12 m, with a weight of around 15,000 kg.

6a00d8341bf67c53ef01538eb766fe970b-800wiIn 2011, more than 400 whale sharks gathered off the Yucatan Coast. It was one of the largest gatherings of whale sharks recorded.


Whale shark description

Whale sharks have a mouth that can be 1.5 m wide, containing 300 to 350 rows of tiny teeth and 10 filter pads which it uses to filter feed. Whale sharks have five large pairs of gills. The head is wide and flat with two small eyes at the front. Whale sharks are grey with a white belly. Their skin is marked with pale yellow spots and stripes which are unique to each individual. The whale shark has three prominent ridges along its sides. Its skin can be up to 10 cm thick. The shark has a pair of dorsal fins and pectoral fins. Juveniles’ tails have a larger upper fin than lower fin, while the adult tail becomes semilunate. The whale shark’s spiracles are just behind its eyes.

Whale sharks stripes and spots

whaleshark_example_rightThe whale sharks patterns are unique to each animal much like a humans finger prints are each unique. Just like  we use fingerprints for identification, whale shark stripes and spots are also used for identifying individual whale sharks for research purposes. Shark Guardian will soon be launching a campaign to encourage people to submit whale shark photos for ID and conservation purposes. Watch this space!

Whale shark diet

Whale shark teethThe whale shark is a filter feeder – one of only three known filter feeding shark species along with the basking shark and the megamouth shark. It feeds on plankton, krill and small squid or vertebrates. It also feeds on small fish and the clouds of eggs and sperm during mass spawning of fish. The many rows of vestigial teeth play no role in feeding. Feeding occurs either by ram filtration, in which the animal opens its mouth and swims forward, pushing water and food into the mouth, or by active suction feeding, in which the animal opens and closes its mouth, sucking in volumes of water that are then expelled through the gills.

The whale shark is an active feeder, targeting concentrations of plankton or fish. It is able to ram filter feed or can gulp in a stationary position. This is in contrast to the passive feeding basking shark, which does not pump water. Instead, it swims to force water across its gills.

Whale shark reproduction

Tag and release of baby whale shark in the PhilippinesNeither mating nor pupping of whale sharks has been observed.

The capture of a female in July 1996 that was pregnant with 300 pups indicated whale sharks are ovoviviparous. The eggs remain in the body and the females give birth to live young which are 40 to 60 cm long. Evidence indicates the pups are not all born at once, but rather the female retains sperm from one mating and produces a steady stream of pups over a prolonged period. They reach sexual maturity at around 30 years and their lifespan is an estimated 70 to 100 years.

On 7 March 2009, marine scientists in the Philippines discovered what is believed to be the smallest living specimen of the whale shark. The young shark, measuring only 38 cm (15 in), was found with its tail tied to a stake at a beach in Pilar, Philippines, and was released into the wild. Based on this discovery, some scientists no longer believe this area is just a feeding ground; this site may be a birthing ground, as well. Both young whale sharks and pregnant females have been seen in the waters of Saint Helena in the South Atlantic Ocean, where numerous whale sharks can be spotted during the summer.

Whale shark and human interaction

As with all marine animals, a strict code of conduct should be practiced to avoid injuring the animal or yourself. Unfortunately many people have witnessed snorkelers and sometimes divers chasing or making contact with whale sharks. This usually frightens the whale shark and will cause the animal to flee and possible not to return. This could change their migration routes in the future if they feel constantly harassed and threatened.

Good code of conduct

Whale shark conservation status

Slide3The whale shark is targeted by commercial fisheries in several areas where they seasonally aggregate. The population is unknown and the species is considered vulnerable by the IUCN. In 1998, the Philippines banned all fishing, selling, importing, and exporting of whale sharks for commercial purposes, followed by India in May 2001 and Taiwan in May 2007.

Bull Shark – Shark of the month

The Bull Shark, also known as the Zambezi shark, is a large predator that is found in warm coastal waters through out the world. Unlike most shark species, bull sharks have the ability to swim and survive in fresh water and can be found thousands of miles up rivers.

Bull Shark Anatomy and Appearance

Bull SharkBull Sharks are not very long sharks, but they tend to be very thick and stocky. The average size of an adult bull shark is about 2.3 meters in length and 130 kg in weight, but specimens have been found up to 3.5 meters long and weighing in at over 300 kg. Like most sharks, they have counter shading meaning that they are gray on top and white on the bottom.

A key feature that separate bull sharks apart from most shark species is their rectal gland. The rectal gland is used for storing and excreting salt from the body, which allows them to control their salinity levels even when they are in freshwater environments.

Bull Shark Feeding

Due to their ability to feed in both freshwater and salt-water environments, bull sharks feed on a vast array of prey species. They feed on numerous bony fish, stingrays, other sharks, birds, turtles, crustaceans, and some mammals. They tend to hunt in murky waters because it allows them to sneak up on their prey. Pound for pound, bull sharks have the strongest bite force compared to all shark species.

Bull Shark Range and Distribution

800px-Carcharhinus_leucus_distmap

Bull sharks are generally found in warm tropical waters with temperatures around 32 degrees Celsius. They are found along the coasts of southern North America, Central America, South America, Africa, the Indian Ocean, as well as the Indo-Pacific near Southeast Asia. Specimens have been reported being seen nearly 2,000 miles up the Amazon and Mississippi rivers as well as being found in golf course lakes after floods.

Bull Shark Reproduction

Bull sharks are viviparous, meaning that they give birth to free-swimming young. They have a gestation period of about one year and can give birth to one to twelve young per birthing. When they are born, adolescent bull sharks are around 65 to 75 centimeters long. They reach sexual maturity after around fifteen years and are about 270 centimeters long at this age.

Conservation Status of Bull Sharks

Slide4Bull sharks are listed by the International Union for Conservation of Nature as Near Threatened. Bull sharks have long gestation periods, reach sexual maturity at a late age, and give birth to few young making them vulnerable to intense fishing and hunting pressures. They are harvested for their fins and meat, which are used to make the prized Chinese dish shark fin soup. Due to their role as apex predators, bull sharks are very important to the environments they inhabit and are a necessity for a healthy reef and ecosystem.

Thanks very much to Brian Stelmar who completed this as part of his Divemaster training program at Hidden Depths on Koh Lanta in Thailand. Hidden Depths is a Shark Guardian Dive Center

Shark of the month: Blue Shark

Blue Shark

The Blue Shark

With our Shark Guardian tour of UK schools underway we wanted to feature a shark in this months ‘Shark Guardian – Shark of the Month’ on the Blue Shark. A shark that is found in and around the waters of the UK and Europe. The Blue shark 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, such as from New England to South America.

Blue sharks can move very quickly. They are viviparous and have been noted for delivering 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”. Maximum lifespan is still unknown, but it is believed that they can live up to 20 years.

Blue shark Anatomy and Appearance

Blue SharkBlue sharks are light-bodied with long pectoral fins. Like many other sharks, blue sharks are counter-shaded, meaning the top of the body is deep blue, lighter on the sides, and the underside is white. The male blue shark commonly grows to 1.82 to 2.82 meters at maturity. Female Blue sharks commonly grow to 2.2 to 3.3 meters at maturity. Large specimens can grow to 3.8 meters long. The Blue Shark is fairly slender in build.

Range and habitat of the Blue Shark

Blue shark Habitat and range

The blue shark is an oceanic pelagic 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.

Feeding

Squid are important prey for blue sharks, but their diet includes other invertebrates such as cuttlefish and pelagic octopus. Whale and porpoise blubber and meat have been retrieved from the stomachs of captured specimens. Blue sharks have been observed and documented working together as a “pack” to herd prey into a concentrated group from which they can easily feed. It is interesting to note that the observed herding behavior was undisturbed by different species of shark in the vicinity that normally would pursue the common prey. The blue shark can swim at fast speeds, allowing it to catch up to prey easily. Triangular teeth allows the Blue shark to easily catch slippery prey.

Conservation and importance

Blue Shark Conservation StatusThe IUCN has classified the Blue Shark as NT (Near Threatened). The Blue Shark is taken in large numbers (an estimated 20 million individuals annually), mainly as bycatch, but there are no population estimates and many catches are unreported. The few fishery assessments carried out suggest relatively little population decline. There is concern over the removal of such large numbers of this likely keystone predator from the oceanic ecosystem.

Shark of the month: Dumb Gulper Shark

Dumb Gulper Shark

 Dumb Gulper Shark  (Centrophorus harrissoni)

The dumb gulper shark is a rare, deep water dogfish found between the east coast of Australia and the north west of New Zealand.  Among other names, it is also known, amusingly, as the dumb shark!

Anatomy and Appearance

These greyish-brown sharks have a slender body and can grow up to 110cm.  They have a long head with a flattened snout, a big mouth and big eyes to help them see at greater depths.

The broad teeth of this species differ between the upper and lower jaws, with the lower teeth being much larger. The teeth also differ between the male and female, with the male having much more erect, upright upper teeth, and upward-curving tips on the lowers.

Feeding

The dumb gulper shark eats most fish, but its most common prey is lanternfish as they are the most abundantly found fish at the depth that the shark lives at.  It also enjoys crustaceans and cephalopods.

Habitat

This shark is found off the east coast of Australia (New South Wales, Victoria, Queensland and Tasmania), and off New Zealand.  It lives in the water column immediately above the seabed on the upper to middle continental slope, usually in depths of 800-1200m.

Reproduction

Females only produce one or two pups every one or two years.

They can live up to 46 years, on average.

Conservation Status

Slide1The dumb gulper shark is listed as critically endangered according to the International Union for Conservation of Nature’s Red List of Threatened Species.  Action is being taken to preserve the shark by the Australian Government, which includes being incorporated into the Environmental Protection and Biodiversity Conservation (EPBC) Act to create a plan to keep this species safe.

 

 

Thank you to Gary Eldridge from Hidden Depths Diving, Koh Lanta, Thailand for this information.

Shark Of The Month: Tiger Shark (Galeocerdo cuvier)

A large macro-predator, the tiger shark derives its name from the dark stripes down its body which resemble a tiger’s pattern. These dark stripes will fade as the shark matures.

Tiger sharks have, over the past 50 years, received a lot of bad publicity due to their perceived aggressive behaviour towards humans. They are second on the list of number of recorded attacks on humans (behind the great white shark). However this is still a very low rate according to researchers. Tiger sharks often frequent shallow coastal waters, including river estuaries, canals and harbours, and are repeatedly found in water almost too shallow for their size. Their preference for this habitat coincides with our penchant for the seaside!

Tiger Shark Anatomy and Appearance

Adult tiger sharks normally grow to a length of 3 – 5m, and a weight of 400 – 650kgs. Even so larger individuals have been recorded. As seems to be the norm with sharks, the females grow larger than the males. It is perfectly camouflaged as, seen from above it is a blue or light green color, and from below it is whitish yellow.

Tiger Shark

It has a wedge-shaped head and this, along with its high back and dorsal fin (located unusually close to its tail). This makes it easy for the shark to turn to the side quickly. Its robust, serrated teeth are specialized to slice through flesh, bone, and other tough substances such as turtle shells.

Tiger Shark Feeding Habits

Tiger Shark Teeth

Tiger Shark Teeth

As an apex predator, it seems the tiger shark will eat just about anything. Fish, crustaceans, sea birds, sea snakes, marine mammals (e.g. dolphins, dugongs, seals and sea lions), turtles, and even other sharks and rays are regularly on the menu. Around the Hawaiian Islands, horses, dogs, sheep, goats, cats and rats are regularly found in their stomachs, mainly due to its scavenging nature. Also scavenged are badly injured or dead whales, and these are found using its excellent sense of smell and great eyesight.

Bizarrely, also found in their stomach are inedible objects such as car number plates, baseballs, oil cans and tyres!

Tiger Shark Habitat

The tiger shark is often found close to the coast mainly in tropical and subtropical waters throughout the world. It is a nomadic shark, guided by warm currents, although preferring to stay nearer the equator in colder months. As previously mentioned, they are regular visitors to the shallows, however they normally live in deep waters that line the reefs, usually around 350m.

Tiger Shark Habitats

Tiger Shark Reproduction

Females mate once every 3 years by internal fertilization. Tiger sharks are ovoviviparous, meaning the eggs hatch inside the female and after a period of 13-16 months young are born live when fully developed. A female can have between 10 to 80 pups, of 51-76cm in length. Tiger sharks reach maturity when they are 2-3m long, and whilst it is not known how long they live for, it is certainly more than 12 years.

Conservation Status of Tiger Sharks

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Tiger sharks are considered a near threatened species due to excessive finning and fishing by humans according to International Union for Conservation of Nature. While shark fin has very few nutrients, shark liver has a high concentration of vitamin A which is used in the production of vitamin oils. In addition, the tiger shark is captured and killed for its distinct skin, as well as by big game fishers. The Tiger Shark is listed as NEAR THREATENED by the IUCN. In 2010, Greenpeace International added the tiger shark to its seafood red list.

Thanks very much to Gary from Hidden Depths Diving on Koh Lanta for this content.

Shark of the month: Swell Shark

The Swell shark, also known as Inflatable or balloon sharks, Cephaloscyllium ventriosum, is a Catshark of the family Scyliorhinidae. A new species of swell shark was only recently discovered in the Philippines in 2011 and locals named it ‘Bubble shark’. When we do our Shark Guardian presentations the children love this name and love the shark as it looks very similar to a leopard shark or juvenile zebra shark.

Swell shark: amazing shark species

Swell shark: amazing shark species

Distribution and Habitat

Swell sharks prefer rocky, algae covered areas

Swell sharks prefer rocky, algae covered areas

Swell sharks are found in subtropical waters close to continental shelves in the eastern Pacific, from central California to the Gulf of California and south to southern Mexico and (possibly) central Chile. This shark prefers rocky, algae-covered areas and are most commonly found at 5 -17m but there are reports of sightings in deeper waters up to 457m deep.

Swell sharks rest during the day in caves and rocky crevices, where they are camouflaged with their surroundings, and then venture out to hunt at night. They feed on small bony fish, mollusks and crustaceans. They actively suck in small fishes or by capturing other prey items by remaining motionless on the bottom with its mouth wide open, waiting for prey to wander in or to be swept in by the currents.

Anatomy and Appearance of the Swell Shark

Swell sharks can grow to about 100 centimeters (39 in) in length and they get their name from their ability to expand their body to about double its regular size. This helps protect it from predators such as seals and larger sharks which may pull it out from rocky reefs, under ledges, and in crevices. If threatened, the swell shark  bends its body into a sharp U-shape, grasps its caudal fin in its mouth and swallows a large quantity of sea water, which makes it swell to twice its normal size. Afterward, they emit a bark-like noise and expel the water returning to their normal size. Are these just the cutest??

Brown blotches and white spots decorate a swell shark’s yellow-brown body with younger swellsharks lighter in color than the older ones. They have a stout body, a flat, broad head, short snout, and a large mouth which contains 55-60 small  teeth in both their upper and lower jaws. Swellshark eyes are large and gold with a nictitating membrane.

A swell shark inflated - its defense mechanism (Photo from mexfish.com)

A swell shark inflated – its defense mechanism (Photo from mexfish.com)

Reproduction

This shark is oviparous (lay eggs) with females laying two flattened green or amber egg sacks which contain the embryo which is attached by two tendrils to a reef. The eggs are pliable and pale at first but develop into hard brown cases within a few hours after birth. The egg cases contain a yolk to provide nutrients to the embryo until it is hatched in 9-12 months. Newborn pups measure 15 cm in length and are able to feed on small mollusks and crustaceans immediately.

A baby swell shark leaving it's egg case

A baby swell shark leaving it’s egg case

Conservation Status and threats

There are no commercial fisheries for the swell shark, however it is considered bycatch in the commercial lobster and crab traps, gill nets, and trawls. This kind of catch has the potential to threaten this shark due to its age at maturity and the low number of young it produces.

The swell shark is sometimes fished recreationally but it is not consumed by humans due to the poor quality of its flesh. Aquariums sometimes include the swellshark in their tanks as it is able to survive captivity for extended periods of time. The World Conservation Union (IUCN) lists the swell shark as a species of “Least Concern”.

Check out this video showing how close a scuba diver can get to these placid sharks:

SOURCES:

Marine Bio

Florida Museum of Natural History

Shark of the month: LEMON SHARK!

Found in sub tropical and tropical waters in the Atlantic and Pacific oceans, the lemon shark can grow to approximately 3 metres in length and weigh approximately 90 kilograms.  It is from the Carcharhinidae family.  There are 57+ species in this family that includes the more popular known Reef and Tiger sharks.

Lemon shark - named because if its skin colour

Lemon shark – named because if its skin colour

Anatomy  and appearance

The lemon shark is aptly named from its body colouration, a soft yellow with white on its belly. This provides a great camouflage for this bottom dweller to hunt its prey of an assortment of bony fish, stingrays, crabs, crayfish and smaller sharks.

There are a few interesting characteristics for lemon sharks, they can adapt to different salinities, their 2nd dorsal fin is as large as their first and they have extremely strong electro-receptor abilities in their snout and generally use this as their guide in hunting as their eyesight is very poor.

Features of a lemon shark

Features of a lemon shark

Reproduction

Females give birth to live young every other year, in shallow nursery waters, up to 17 pups at one time. The lemon shark fends for itself from birth and will stay in the shallow waters until they grow larger. They do not reach sexual maturity for 12-15 years and the average lifespan is only approximately 25 years.

See this video for a lemon shark giving birth!

Habitat

The choice of habitat of the lemon shark may be its worst enemy for two reasons.  They are generally found in shallow to moderate depth (92 metres) mangroves, estuaries and coral reefs so although it is being hunted for meat and shark fin soup; coastal development and the destruction of the mangroves is its biggest threat.  Secondly, the Lemon shark has been found to have a very high survival rate in captivity possibly lessening the responsibility to ensure its natural habitat is preserved.

Lemon Shark

Lemon Shark – found in shallow reefs and mangrove areas

Cosnervation status

The IUCN class the lemon shark as vulnerable and in South East Asia it is endangered. This is believed to be due to the widespread destruction of coral reefs and mangrove habitats as mentioned above.

Written by Sarah Chernecki

PADI Master Scuba Diver Trainer

Resources:

BBC Nature Wildlife

Marinebio.org

Marinelife.about.com

Sharks-world.com

Shark of the month: Thresher Shark

 

Thresher sharks are definitely a favourite amongst school children Shark Guardian present to. With their long, distinctive tails and graceful movement in the water, they are definitely at the top of scuba divers’ lists for sharks they would like to see. There are 3 species of thresher shark and all tend to be solitary creatures.  Although they do not appear to be a threat to humans there have been reports of divers being hit by their tail!

Thresher Shark - Malapascua, Philippines

Thresher Shark – Malapascua, Philippines

Anatomy and Appearance

Its name derives from the greek word for fox. Its impressive caudal fin can be as long as the body itself.  This is its main identifying feature and is easily recognized.  It has a short head with a cone shaped nose and teeth of varying size.  It has 5 gill slits.  The largest species (common thresher) achieves 6m in length.  Overall their colouration is a brown, blueish, purple dorsally and a lighter shade ventrally. The picture below shows the differences in species colour.

Thresher sharks: Shark Guardian presentations

Thresher sharks: Shark Guardian presentations

Feeding

Threshers are known to follow large schools of fish, including tuna, bluefish and mackerel. They also eat squid and cuttlefish.  Their tail is used to herd the fish, using it as a weapon to stun their prey by ‘slapping’ the water.  The thresher shark is a very strong swimmer and are one of the few species known to jump fully out of the water, making turns just like dolphins do. Check out the photo below showing a thresher doing just that, sighted off the coast of Wales by the Sea Trust in the UK in 2013!

Jumping Thresher shark via Sea Trust

Jumping Thresher shark via Sea Trust

 

Habitat

Found in all temperate and tropical oceans of the world, including the eastern and western Atlantic, central Pacific and Indo-west Pacific.  Populations are separated by depth and space according to gender.  Although they can be sighted in shallow inshore waters, they prefer the open ocean at maximum depths of 500m.

Reproduction

The thresher sharks have no distinct breeding season, with litters usually of 2-4 pups and a gestation period of 9 months. They are slow to mature but can live upwards of 20 years.

IUCN Status

Vulnerable

This genus of shark is highly vulnerable to overfishing, hunted for their meat, liver oil and fins.

Clare Walkden

Clare Walkden

Written by Clare Walkden (Divemaster trainee from Hidden Depths Dive Center on Koh Lanta, Krabi, Thailand) with edits by Shark Guardian

To find out more about Thresher sharks follow the blogs of Shark Guardian dive center Malapascua Exotic in the Philippines.

 

April Shark of the Month: ZEBRA (LEOPARD) SHARK

Adult zebra sharks have longitudinal ridges on the body and a spotted pattern

Adult zebra sharks have longitudinal ridges on the body and a spotted pattern

Zebra Sharks (Stegostoma fasciatum or varium)

Known by most of us in Thailand as Leopard sharks, these are one of Shark Guardians favourite sharks due to their beautiful colouring and friendly nature. An experience not to be missed as a diver is when you are able to get close to these sharks whilst moving slowly on the sea bed, as they rest on the sea bed too. Unfortunately sightings of them are becoming more and more rare but we hope with some monitoring by divers, we can play a part of their come back.

Anatomy and Appearance

There is no size difference between males and females and they can grow to a length of 3.5m, with its tail (or lower caudal fin to give it its proper name) making up nearly half of that length.  It has small barbels on its snout, a small mouth, and small eyes.  Its teeth are pointed, with each tooth having two smaller, lateral, flanking points.  Prominent ridges run along its flanks.

The name leopard comes from its’ adult appearance, the beautiful leopard print it displays. In our presentations we love showing the juvenile Zebra shark photos as you get an idea why really they are zebra sharks…

A juvenille zebra shark with a colouring in between that of an adult and a young shark

A juvenille zebra shark with a colouring in between that of an adult and a young shark

Habitat and Migration

Nothing scary about this little baby shark!

Nothing scary about this baby shark!

Found throughout the tropical indo-pacific region on sandy flats, in and around coral reefs, to depths of 62m, the zebra shark gets its name from the juvenile of the species which has a stripped pattern (see above!).  Zebra sharks are more commonly known as leopard sharks in and around the Andaman Sea, but this is confusing as there is another species of shark called the leopard shark (Triakis semifasciata) found along the Pacific North American coast.

 

Diet

Zebra sharks are generally nocturnal hunters, eating crustaceans, molluscs, small bony fish, and they even enjoy the odd sea snake.

Life History

They are solitary creatures although they do form large seasonal congregations of between 20 and 50, with females outnumbering males by three to one.  The reason for this is unknown, although we do know it is definitely not for mating.

In order to mate, males attract females by vigorously biting their fins!  If he is lucky, the male is then allowed to mate with his chosen ‘victim’.  17cm long brown or purplish black eggs are then laid and attached to the substrate.  The eggs can take between 4 and 6 months to hatch.  When the young eventually appear, they are about 20-36cm long.

They can live for up to 30 years.

Conservation

vulnerable

They are preyed upon by larger fish and marine mammals.  However, it is humans that provide the greatest threat to its existence.  Their status with the World Conservation Union is ‘Vulnerable’ due to humans hunting them for their meat, fins and liver oil.  Numbers are dwindling rapidly as they are an easy catch due to their relatively shallow habitat.

Beautiful, elegant swimmers of the sea

Beautiful, elegant swimmers of the sea

Docile and generally slow-moving, they are not dangerous to humans.  However, they have bitten divers who pull their tails and try to ride them.  In fairness, I would get upset if a stranger tried to jump on my back and ride me!

Spot the Leopard Shark: Thailand is a joint venture between Thai researchers (Phuket Marine Biological Center) and Australian researchers (The University of Queensland) and the diving community of Thailand. Shark Guardian is pleased to help promote this project in Thailand. Please get involved, spread the word and contribute your photographs. And of course, if you identify a new shark to the database you get to name it!

Shark of the month: OCEANIC WHITETIP

The Oceanic White Tip Shark

The Oceanic White Tip Shark

Last month we told you all about the porbeagle shark as it was 1 of the 5 shark species to be discussed at CITES (The Convention on International Trade in Endangered Species) this month, possibly to go on to Appendix 2. Well as we’ve been keeping you up to date about this you will all know all species were successful! So to continue this vibe, Shark Guardian brings you one of the other successful sharks: the Oceanic Whitetip!

Considered one of the 5 most dangerous sharks in the world, they can grow to nearly 4 meters in length and are named because all its rounded fin tips are white or show mottled white patterns.

Read full blog

Shark of the month: PORBEAGLE SHARK

The Porbeagle shark was our focus for shark of the month in February 2013 since CITES (The convention on International trade in endangered species) was approaching at the beginning of March, 2013. This is one of the lesser known sharks, but one which is in real danger of disappearing from our waters unless they get extra protection. Fortunately in March they they joined Appendix 2 which means they now have better regulation for their trade Internationally. The large, warm-blooded porbeagle shark (Lamna nasus) is distributed throughout the temperate north Atlantic and southern hemisphere. It is a species of mackerel shark from the family Lamnidae which also includes white sharks.

Porbeagle shark: Lamna Nasus

Porbeagle shark: Lamna Nasus

A shark species under threat

Demand for its large fins as well as its meat has driven populations to very low levels. Recent assessments show that because porbeagle populations have been severely depleted, it is unable to fulfill its key role in the marine ecosystem. Porbeagle populations are reduced by about 70 percent of their historical levels wherever they are found, and in some places declines are even steeper.

Anatomy and Appearance

This shark typically reaches 2.5 m (8.2 ft) in length and a weight of 135 kg (300 lb); North Atlantic sharks grow larger than Southern Hemisphere sharks and differ in coloration and aspects of life history. Gray above and white below, the porbeagle has a very stout midsection that tapers towards the long, pointed snout and the narrow base of the tail. It has large pectoral and first dorsal fins, tiny pelvic, second dorsal, and anal fins, and a crescent-shaped caudal fin.

Porbeagle Teeth

Porbeagle Teeth

Porbeagle Shark Teeth

North Atlantic sharks have 28–29 upper tooth rows and 26–27 lower tooth rows. Southern Hemisphere sharks have 30–31 upper tooth rows and 27–29 lower rows. One of the distinctive features of porbeagle sharks are its three-cusped teeth. Each tooth has a strongly arched base and a nearly straight, awl-like central cusp. This is flanked by a pair of smaller cusplets in all but the smallest sharks.

 

Porbeagle tail demonstrating the keels which give the shark swimming power

Porbeagle tail demonstrating the keels which give the shark swimming power

Distinguishing Features

Other features which make it stand out from other sharks are the white blotch at the base of its first dorsal fin, and the two pairs of lateral keels on its tail. The eyes are large and black, without nictitating membranes (protective eyelids) .


Habitat and Migration

The porbeagle inhabits water down to a depth of 1360 meters (4,200 feet) and favors water temperatures of 5 to 10 °C (41 to 50 °F). They have a heat regulating system that raises the body temperature several degrees above the water temperature, which allows it to live efficiently in some cooler waters.

Seasonal migrations have been observed in porbeagles from both hemispheres and it is believed the migrating sharks may travel upwards of 2,300 km (1,400 mi). Once they reach their destination they tend to remain within a relatively localized area. The shape of the shark plus the extra keels on its tail give it the ability to swim these huge distances and also give it extra power. This is why it is one of the fastest sharks.

Feeding and habits

This stocky shark is often included in studies on whether or not sharks play. That is because several observers have reported seeing porbeagles in groups of up to 20 individuals manipulating and tossing about floating objects, including lumber and seaweed. They seem to engage in such activity for no apparent reason other than to pass the timel!

The porbeagle shark mainly feeds on schooling fish, such as mackerel, herring, cod, hake, lancetfish, redfish and haddock. It will also consume shellfish, smaller sharks (e.g. some dogfish species) and squid. The side projections on the teeth of adults help them to gnash through tough prey.

Life history

Like other members of its family lamnidae, the porbeagle is a placental viviparous with oophagy. This means that the main source of embryonic nutrition are unfertilized eggs. Some developing embryos will also feed on less developed siblings (cannibalisim) so that even though up to 200,000 unfertilised eggs are produced, only 2-4 pups will survive.

Both sexes grow at similar rates until the onset of maturation, with females maturing later and at a larger size than males. The maximum lifespan of this species appears to be 30–40 years in the Atlantic, but could be as much as 65 years in the South Pacific.

Conservation status of the porbeagle shark

Populations of the porbeagle have been severely depleted around the globe. The International Union for the Conservation of Nature (IUCN) Red List of Threatened Species assessed the porbeagle as Vulnerable globally, Endangered in the northwest Atlantic and Critically Endangered in the Mediterranean and northeast Atlantic. The porbeagle falls into the United Nations Food and Agriculture Organization’s (FAO) lowest productivity category, meaning it has an extremely low reproductive capacity and thus is particularly vulnerable to overexploitation. It is also one of the ocean’s most vulnerable species.

Porbeagle shark - one of 30 species found in UK waters, classed as Vulnerable to Extinction by IUCN

Porbeagle shark – one of 30 species found in UK waters, classed as Vulnerable to Extinction by IUCN

Proposals to list the species in CITES Appendix 2 in 2008 and again in 2010 were rejected. We were really happy that at this years CITES meeting this amazing shark finally started to get some if the protection it deserves.

More Information

For more information on porbeagle sharks and their research please see the Canadian Research Laboratory who we credit for some of the photos used in this blog.