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

Slide6

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.