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Ragged Tooth Sharks

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Diving with Ragged Tooth Sharks

It is all about sex - the Ragged Tooth Sharks come here (no pun intended) to either mate or rest up before the next year's session!

Diving with Ragged Tooth Sharks in South Africa is easy - June through to October are good months to find them at Aliwal Shoal and Protea Banks and during February to May the hang out at Sodwana Bay - experienced guides know where to find them and will teach you how to safely and responsibly dive with the sharks.

Ferocious as they may seem, the Ragged Tooth Sharks are not aggressive at all -in fact their inquisitiveness often cause inexperienced divers air consumption to go through the roof!

Taxonomy
The Ragged Tooth Shark (Sand Tiger or Grey Nurse Shark)was originally named Carcharias taurus by Rafinesque in 1810. Since then it has also been referred to literature as Odontaspis taurus, Eugomphodus taurus, Odontaspis americanus, Squalus americanus, Carcharias griseus, Odontaspis arenarius, Carcharias arenarius, Odontaspis platensis, and Carcharius platensis.

Common Names
English language common names include Ragged Tooth Shark (Sand Tiger or Grey Nurse Shark) shark, grey nurse shark, ground shark, spotted raggedtooth shark, slender-tooth shark, spotted Ragged Tooth Shark (Sand Tiger or Grey Nurse Shark) shark and ground shark. Other common names are bacota (Spanish), pintado (Spanish), sarda (Spanish), cação-da-areia (Portuguese), mangona (Portuguese), tavrocarcharias (Greek), chien de mer (French), kalb, (Arabic), grauer sandhai (German), hietahai (Finnish), karish khol pari (Hebrew), oxhaj (Swedish), zandtijgerhaai (Dutch), peshkaqen i eger (Albanian), shirowani (Japanese) and spikkel-skeurtandhaai (Afrikaans).

Distinctive Features
The most distinctive feature of the Ragged Tooth Shark is it's teeth - ferocious looking and always visible the ragged tooth Sharks grin can hardly be mistaken for any other shark.

The Ragged tooth Shark is a large, bulky shark with a flattened conical snout and a long mouth that extends behind the eyes. The first dorsal fin is set back and is much closer to the pelvic fins than the pectoral fins. The anal and dorsal fins are large and broad-based and the second dorsal fin is almost the same size as the first dorsal. Gill slits are anterior to the origin of the pectoral fins in this species. The caudal fin of the Ragged tooth Shark is asymmetrically shaped with a strongly pronounced upper lobe.

The Ragged tooth Shark grows to a length of 3.6m. Males mature at 2.1m and females at 2.2m. Average size ranges from four to nine feet with maximum length believed to be around 10.5 feet (320 cm) in females and 9.9 feet (301 cm) in males. Male maturity is reached at 6.3 feet (190-195 cm) at four to five years of age. Female maturity is reached at six years or over 7.2 feet (220 cm) in total length. Individuals in aquariums have lived to be 16 years old.

Many bony fishes have a structure called a swim bladder which is used to control buoyancy. No shark has a swim bladder. Instead, sharks have different buoyancy regulating mechanisms that involve the liver and fins. The oily liver of the Grey Nurse Shark has been developed to a huge degree and occupies a large proportion of the body cavity. Shark oil is lighter than seawater and this gives the shark buoyancy. The Ragged tooth Shark also swallows air at the surface, and holds it in the stomach. This provides buoyancy and enables the shark to hang almost motionless above the bottom.

Ragged Tooth Sharks have extremely small eyes but no Nickhaut (a third eyelid which it can pull over its eyes, a feature found, e.g. with gray sharks).

Sharks have the same five senses as humans; taste, touch, sight, hearing and smell, but in addition have a sixth sense; electroreception. The underside of the Ragged tooth Shark's snout is dotted with pores. Each of these leads to an organ (ampula of Lorenzini) which can detect electricity.

Coloration
The Ragged Tooth Shark is a distinctive fish which is usually grey-brown on top and a dirty white underneath. Many fishes that swim in open water are counter shaded. This adaptation results in the fish being difficult to see from above because the dark colour of the dorsal surface of the fish blends into the dark colour of the water below.

It helps to make the fish also less visible from below because the light colour of the underside of the fish is less noticeable against the light shining from above. Ragged Tooth Sharks are counter shaded, the dorsal (upper) part is dark, mostly a grey to bronzy colour whereas the ventral (lower) part of the body is pale.

Juveniles have reddish or brownish spots on the posterior (back) half of the body and tail. These spots often fade as the shark ages, but are sometimes still visible on adults.

Dentition
The teeth of the Ragged Tooth Shark (Sand Tiger or Grey Nurse Shark) have prominent narrow cusps with lateral cusplets. The upper anterior teeth are separated by small intermediate teeth. Dermal denticles are loosely spaced and ovoid lanceolate shaped with three ridges. The axial ridge is prominent and sharp-edged interiorly but usually is subdivided and flat-topped posteriorly.

In individuals around 3.3 feet (100cm) long denticle sizes are about 0.016 inches (0.4mm) broad by 0.018 inches (0.45mm) long. The upper teeth number 44 to 48 and the lower teeth number 41 to 46. The teeth in the corners of the mouth are very small and numerous. The ragged looking teeth give the Ragged Tooth Shark (Sand Tiger or Grey Nurse Shark) a distinct menacing look. The teeth of the Ragged Tooth Shark are constantly being replaced. This means that older, damaged or blunt teeth on the exterior surfaces of the jaws are replaced by new teeth. In the whaler sharks, family Carcharhinidae, each tooth is replaced every eight to fifteen days. Ragged Tooth Sharks can have up to 30,000 teeth during it's lifetime.

Distribution
The family Odontaspidae is recorded throughout the world oceans. Ragged Tooth Sharks are found in tropical and temperate waters in the Atlantic, Indian and western Pacific Oceans except for the eastern Pacific. In the western Atlantic Ocean it ranges from the Gulf of Maine (U.S.) to Argentina and is commonly found in Cape Cod (U.S.) and Delaware Bay (U.S.) during the summer months.

In the eastern Atlantic it can be found from the coast of Europe to North Africa and within the Mediterranean Sea. Its range also extends from Australia to Japan and in the waters off South Africa. In South Africa the sharks are commonly found on the East Coast.

Habitat
Commonly found inshore ranging in depths from 6 to 626 feet (1.8 to 191 m), the Ragged Tooth Sharks range extends to a variety of areas including the surf zone, shallow bays, coral and rocky reefs and deeper areas around the outer continental shelves. C. taurus is often found on the bottom but can also be seen throughout the water column.

They are normally seen during the day in sheltered gutters or caves where they hover almost motionless, a talent made possible by their ability to swallow air at the surface which counteracts the natural tendency for all sharks to sink.

These sharks are quite sociable, often gathering together in small to huge schools of mixed sex and size. During the day, they are generally found in the vicinity of drop-offs, caves and ledges hovering just above the surface either singly or in small groups.

The Ragged Tooth Shark is migratory within its region, moving pole ward during the summer while making equatorial movements during the fall and winter months.

Their social and curious nature allows divers to make close contact but they should never be cornered or harassed as they will bite with lightening speed if threatened. From a motionless hover they can accelerate instantly to catch fast-swimming kingfish or salmon, so fast in fact that their tail creates a cavity in the water causing a deep boom to be heard.

Diet
The diet of this ravenous feeder mainly consists of a wide variety of small bony fish including herrings, bluefishes, flatfishes, eels, mullets, snappers, hakes, porgies, croakers, bonito, remoras, sea robins and sea basses. Other prey items of the Ragged Tooth Shark (Sand Tiger or Grey Nurse Shark) are rays, squids, crabs, lobsters and on rare occasions other smaller sharks. According to reports this species also goes hunting together, driving together swarms of fish and thus making them easy prey.

Reproduction
Males and females are sexually mature when they reach a length of approximately 220 cm. Juveniles are born alive and measure approximately 100 cm in length at birth. The Ragged Tooth Sharks has an interesting twist to its reproduction, which begins, like all sharks with internal fertilization. The Ragged Tooth Shark is ovoviviparous, it produces eggs which hatch inside the female and have no placental connection.

The developing young are enclosed in egg cases about 55 mm in length within each uterus of the female. Usually only one pup survives in each uteri since the largest embryo ends up eating all of its smaller siblings during the gestation period of about nine (At 6.7 inches (17 cm) embryos have functional teeth and are feeding and at 10.2 inches (26 cm) they are able to move in utero). This generally limits litter sizes to two pups.

At birth they measure one meter in length, which considerably increases their chances of survival since it reduces the number of their natural predators.

Predators
Juveniles are susceptible to predation by larger sharks. Mature individuals have no major predators.

Distinctive Behaviour
Since the Ragged Tooth Shark is denser than water and lacks a swim bladder like bony fish, it has adopted a behaviour that allows it to become neutrally buoyant in the water column. The shark comes to the surface and gulps air, which it holds in its stomach. This allows the shark to hover motionless in the water. Ragged Tooth Shark are often found in large groups which gather to mate or go hunting. Latest observations show that Ragged Tooth Shark display a distinct social behaviour. They like to linger socially underneath cliff overhangs or similar structures, remaining there motionless - with the help of swallowed air - for longer periods of time.

Importance to Humans
In the North Pacific, northern Indian Ocean and off the tropical west coast of Africa, the Ragged Tooth Shark is commercially fished for food. The meat is utilized, fresh frozen and dried-salted, fins are sold in oriental markets for shark fin soup and jaws and teeth are used for trophies and ornaments. The Ragged Tooth Shark is not a commercially targeted species in North American waters, partially due to its protected status. In some instances in Australian waters the Ragged Tooth Shark had been killed by divers using underwater weapons since it is slow moving and approachable.

This practice was banned in Australia in 1984. Ragged Tooth Shark survive very well in aquariums and are a favourite because of their large size and fierce look. This shark also inhabits coastal waters and popular dive sites, such as shipwrecks, where they can be observed by recreational divers.

Danger to Humans
Underwater observations of this shark reveal that it is not aggressive unless provoked. Its size and jagged teeth demand respect and have given it an undeserved reputation as a man-eater in Australia, where it is often confused with other species, mainly requiem sharks. It has been known to attack people when provoked, especially when they are spear fishing. There have been accounts of Ragged Tooth Sharks (Sand Tiger or Grey Nurse Shark) stealing fish off stringers and spears underwater. In total there have been relatively few documented attacks on humans.

Conservation
Based purely on its fearsome looks this shark was once blamed for most shark attacks on humans and was hunted and fished to near extinction. Today the docile Ragged Tooth Shark enjoys protected status in some Australian States.

It is the first shark in the world to be protected by law. In the past, the Ragged Tooth Shark has been hunted throughout its range, and the flesh is particularly prized in Japan. The oil and fins are also in demand; in the 18th and 19th Centuries the shark was persecuted in large numbers for its liver oil that was used in lighting.

Currently Ragged Tooth Shark are regulated in the commercial long line shark fishery on the east coast of the United States by the National Marine Fisheries Service where it is identified as a prohibited species. Any Ragged Tooth Shark caught must be immediately released with minimal harm to the shark. The World Conservation Union classifies the Ragged Tooth Shark as "Vulnerable", which means it faces a high risk of extinction in the wild in the medium term future. This is due to an observed, estimated, inferred or suspected reduction in the population of at least 20% over the last 10 years or three generations.

Since the Ragged Tooth Shark’s reproductive rate is very low, only one or two pups per mature female every one or two years, the population needs to be closely monitored. Catch rates of populations in Australia and South Africa have shown declines due to commercial fishing, spear fishing and beach meshing. Even with status as a protected species, the recovery of the Ragged Tooth Shark off the coast of Australia has been very slow.

Sources
www.sharks.com
www.enchantedlearning.com
www.austmus.gov.au
www.flmnh.ufl.edu
www.boattalk.com
www.conservationinstitute.org
www.flmnh.ufl.edu/fish/Gallery/Descript/Sandtiger/Sandtiger.html
www.sharkinfo.ch/SI1_00e/ctaurus.html
www.marinethemes.com/greynurse.html
www.redlist.org
www.fishbase.org
www.arkive.org/species/GES/fish/Carcharias_taurus/more_info.html
www.fishbase.org/Summary/SpeciesSummary.php?id=747

Further reading