Sand sharks (Carcharias taurus) are large sharks that have many jagged teeth that make them look like a vicious predator. However, Sand sharks are docile and only attack humans when provoked.
They got the “Sand” portion of their name from being seen around shallow waters and coming close to shore. Sand Sharks occur worldwide in tropical and temperate waters.
Kingdom – Animalia
Phylum – Chordata
Class – Chondrichthyes
Order – Lamniformes
Family – Odontaspididae
Genus – Carcharias
Species – C. taurus
Because of these sharks’ worldwide distribution, they have many common names such as sand tiger sharks, grey nurse sharks, spotted ragged-tooth shark, and blue nurse sand tiger. The name “grey nurse shark” is more common in the united kingdom and Australia, and it is the second most used name for these sharks.
Taxonomy of Sand shark
Sand tiger shark description as “Carcharias taurus” by Constantine Rafinesque came from a specimen captured off the coast of Sicily. Carcharias taurus means “Bull shark” in English.
Scientists have varying opinions about this taxonomy classification. As a result, after twenty-seven years of Rafinesque’s original description of this shark, German Biologists Henle and Muller changed the genus name from Carcharias to Triglochis.
A year after, Swiss American naturalist Jean Louis Rodolphe Agassiz classified it again as Odontaspis cuspidata based on fossilized teeth samples. Agassiz’s classification remained valid until 1961 when three Ichthyologists and paleontologists, E.I. White, W. Tucker, and N.B. Marshall requested that Scientists return this shark to genus Carcharias. However, ICZN, which is the International Code of Zoological Nomenclature, did not approve their request, thus, approving Odontaspis. When Researchers agreed that taurus belongs after Odontaspis, they changed the name to Odontaspis taurus.
In 1977, Follet and Compagno challenged the Odontaspis taurus name and replaced Odontaspis with Eugomphodus, a kind of unknown classification. Many taxonomists queried this change, arguing that there was no critical difference between Carcharias and Odontaspis.
After changing the name to Eugomphodus taurus, Follet and Compagno successfully advocated in establishing the shark’s current scientific name as Carcharias taurus. The ICZN approved this name, and till today, biologists still use it.
Description of Sand Sharks
Sand sharks are large sharks with Bulky, stout, and fusiform body. They are brownish-gray in color with reddish-brown spots scattered on the hind part of their body and a white color underneath. These sharks have a flattened, Cone-shaped snout and an elongated tail that distinguished them from other sharks.
They have three rows of needle-like teeth that are highly adapted for impaling fish, which is their main prey. Another fact that separate these sharks from many other sharks are their lack of nictating membrane (extra eyelid) that protect the eyes during attacks and feeding.
Sand sharks gill slits are anterior to the origin of their pectoral fins. Their eyes are very small. They also have anal fins and two dorsal fins that are almost similar in size. Although Sand sharks have a vicious appearance, they are quite harmless.
Migration of Sand Sharks
Sand sharks in Australia and South Africa undertake an annual migration that may cover more than 620 mi (1,000 km). They give birth during the summer in relatively cold water (temperature 61°F).
After giving birth, Sand sharks swim northwards towards areas where there are suitable caves or rocks, sometimes at a water depth ca. 66 ft (20 m), where they mate during and after winter. For these sharks, mating normally occurs at night. After mating, sand sharks swim further north to warmer waters, which is where their gestation takes place.
During autumn, they return southward to give birth in cooler waters. Young sand sharks do not take part in this migration. But, they seem to move into deep waters during winter because they are usually absent in their birth grounds.
At Cape Cod, USA, Sand sharks juveniles move away from coastal areas when water temperature decreases to less than 16 degrees Celsius, and the length of the day decreases to less than 12 h. However, they return to their usual summer haunts when the temperature goes back to normal.
Sand sharks live in the Pacific, Atlantic, and Indian Oceans and the Adriatic and Mediterranean Seas. In the Northern Atlantic, Sandsharks range from the Gulf of Maine to Florida and into the Gulf of Mexico.
Sand sharks are very common in southern New England and the westerly entrance to the Gulf of Maine. They are plentiful at woods Hole from around June to November. These sharks are common anywhere in that region in shoal waters, even coming up to the wharves. Also, at Nantucket, Sand sharks are abundant that shark fishing with them as the main objective is a famous sport.
In August 1947, divers saw a large sand shark at the surface pursuing a striped bass that was being dragged aboard a fishing boat on a hand line in the east of the Cape Cod Bay. Fishermen said it was not an unusual happening in the area. Still, Cape Cod Bay seems to be the northern boundary to their occurrence in any regularity or numbers.
These sharks often occur in shallow bays, coastal waters, estuaries and tropical or rocky reefs. Although sand sharks live in shallow waters, they also swim down to depths of about 200 meters. Sand sharks are usually resting on the ocean bottom during the day, remaining motionless while they float in the water column by the use of their buoyancy control. The name sand sharks come from their ability to migrate towards shoreline habitats.
Sand sharks are strong but slow-moving. They are relatively sluggish sharks that spend most of their time near the ocean bottom looking for food. These sharks swim to the surface of the water to swallow air, retaining it in their stomach to create near neutral buoyancy that allows them to remain motionless above the seafloor. Sand Sharks are the only sharks that exhibit this behavior.
Despite their fearsome appearance, Sand sharks are naturally not aggressive unless provoked; they have less tolerance for divers with fins and spears.
Generally, Sand sharks are free thinkers and fend for themselves. But sometimes, they form groups of about 20 or more.
Sand sharks have a unique hunting strategy. They can gulp air from above the surface and collect it into their stomach. This strategy aids their buoyancy and enables them to approach their prey virtually motionless. In daylight, you can find sand shark mostly inactive, taking shelter near rocks, caves, overhangs, reefs most times at relatively shallow depths.
However, at night, they become very active and resume their hunting activities. Sand sharks hunt small fish and even known sometimes to attack full fishing nets. Aquarium observers pointed out that when sand sharks come close enough to their prey, they grab it with a quick sideways snap. These sharks when observed tend to gather in hunting groups when preying on large schools of fish.
Feeding and Diet
Sand sharks are relatively sluggish, living mostly on the bottom. Their diet consists of large and small bony fishes, rays, small sharks, crabs, lobsters, and squid. The majority of these sharks prey items are demersal, I.e., from the sea bottom.
In Argentina, their prey includes majorly demersal fishes, e.g., the striped weakfish (Cynoscion guatucupa). They also feed on benthic rays and skates as prey. The stomach content analysis of Sand sharks juveniles shows that they feed more on sea bottom prey than benthic prey.
Off South Africa, a sand shark of not up to 2 m in length prey on fish of about a quarter of its length while Large sand shark capture prey up to about half its length. These sharks sometimes hunt cooperatively to feed on schooling prey.
Sand Shark Size and Growth Rate
During the first year, Sand sharks grow to about 27 cm. After that, their growth rate decreases by 2.5 cm each year until it stabilizes at about 7 cm per year. These sharks’ males reach sexual maturity at the age of five to seven years at about 6.2 ft in length. Their females also reach sexual maturity at approximately 7.2 ft (2.2 m) long at about seven to ten years of age.
Adaptations for Survival
Like most other sharks, Sand sharks can detect electrical signals emitted by potential prey in the water substrate or column. With the specialized sensory organs on the sides of their head and lower jaw known as Ampullae of Lorenzini, sand sharks are capable of finding their prey in murky water.
These sharks also have acute senses of touch, smell, and hearing. Sand sharks can discriminate between dark and light objects. They have a very good vision and are sensitive to low light conditions. Their adaptations of electrical reception, smell, and hearing combine to make them feared predators.
The Countershading of Sand sharks’ body is a protective camouflage. If a predator looks down at these sharks, their top blends into the sea below. When viewed from below, the white color underneath blends into the lighter water columns.
Threats and conservation status of Sand Sharks
In places like India, Ghana, and Pakistan, catching of Sand sharks is usually by fishing trawlers or with a fishing line. This species attract high price as a food item. In North America and Japan, they are majorly fished for their fins. Sand sharks liver oils are a popular product in cosmetic products like lipstick.
They are highly sought after by anglers in a fishing competition in South Africa and some other countries. Sand sharks are also priced as an aquarium exhibit in the united states, Australia, South Africa, and Europe because of their docile nature. Sand sharks also reproduce at an unusually low rate because they do not have more than two pups at a time and reproduce every 2 or 3 years.
All of these are the main contributors to the population decline of these sharks. Records have shown that sand sharks have reduced significantly since 1980. Many Sand sharks are caught entangled in shark nets and either taken or strangled by fishermen. Many estuaries along the united states of America eastern Atlantic coast houses a lot of juvenile young sharks.
These estuaries are vulnerable to non-profit source pollution that is hazardous to the pups. In eastern Australia, Scientists estimated the breeding population of these sharks to be fewer than 500 reproductivity mature sharks, which is too small to sustain a healthy population.
These sharks lists as “Vulnerable (VU)” on the International Union for Conservation of Nature (IUCN). Sand sharks also listed as “Endangered” species under Queensland’s Nature Conservation Act 1992.
According to NMFS (National Marine Fisheries Service), any shark that is caught must be released back into the ocean alive with minimal harm. Sand sharks are considered prohibited species making it illegal to harvest them on the united states Atlantic coast
Mating and Courtship
Sand sharks mating occurs around March and April in the northern hemisphere and during August- October in the southern hemisphere. From observations, the females tend to linger just above the sandy bottom when they were receptive.
This behavior prevents their males from approaching them from underneath towards their cloaca. Most times, there is more than one male close by with the dominant male remaining closer to the female. This dominant one discourages others by the aggressive display. Afterward, the dominant male shark closely follows the tail of the subordinate, forcing the subordinate to swim away.
The dominant male approaches the female, and the two sharks show strong interest by biting. Thus, the male bites the anal and pectoral fin areas of the female. In turn, the female Sand shark responds by superficial biting of the male. They continue this behavior for several days, during which the male patrol the area around the female shark.
The male often approaches the female in nosing behavior to smell the cloaca of the female. If the female sand shark is ready, she swims off with the male, and both sharks wring their bodies so that the right clasper of the male shark enters the cloaca of the female.
During the process of mating, the male bites the base of the female right pectoral fin, leaving visible scars on its body. After two or three minutes, they are done mating, and the two separate. Female sand sharks are known to mate with more than one male. Once mating is complete, the female remains behind while the male moves away to seek another area to feed. This results in many observations of these sharks population comprising of exclusively female.
Sand Sharks reproductive pattern is similar to that of the Lamnidae, the family in which they belong to. These sharks are Ovoviviparus, that is, the eggs hatch inside the mother. They only develop two embryos, one in each uterus. The strongest and largest embryos consume their siblings in the womb before each surviving pup is born.
Their gestation period lasts for about 12 months. These sharks usually give birth during winter, which is quite odd for sharks. Unlike other sharks, Sand sharks only give birth to 1 to 2 live pups of about 3.3 ft at a time. They only reproduce after two or three years.
Relationship with Humans
Attacks on Humans
Sand sharks are often thought to be deadly or vicious because of their appearance. However, these sharks are docile and pose no threats to humans. Their mouth is not large enough to cause any serious injuries. Sand sharks roam the surf, sometimes close to divers.
There have not been any record of unprovoked attacks from these sharks; most attacks are associated with spearfishers who usually provoke them. Instead of attacking humans, When Sand tiger sharks become aggressive, they tend to steal bait or fish from fishing lines. Due to its large size and docile nature, Aquarium keepers display Sand shark in aquariums around the world.
Competition for Food with Humans
In places like Argentina and South Africa, the prey items of sand shark are greatly fished for important commercial fisheries.
Nets Around Swimming Beaches
In South Africa and Australia, one of the common practices in beach holiday areas is putting Shark nets around the beaches often used by swimmers. These shark nets are erected to about 1,300 ft from the shore and act as gills nets that trap incoming sharks. It was the usual practice until 2005.
In South Africa, the mortality of sand shark caused a substantial decrease in the rate of these animals. Scientists later concluded that the shark nets pose a significant threat to these species that have a low reproductive rate.
Before the year 2000, these shark nets snagged about 200 sand sharks per year in South Africa, of which only about 40% survived and were released back into the ocean alive. Scientists are now working on an alternative approach.
Scuba Diver’s Effect
Sand shark is targeting for scuba divers who wish to photograph or observe these sharks. Research near Sydney in Australia observed that the proximity of scuba divers may affect the behavior of these sharks.
Diver activity affects the swimming, aggregation, and respiratory behaviors of sand tiger sharks, but only on a short time basis. Group size of scuba divers is less important in affecting these sharks’ behavior, unlike the distance at which these divers approach the sharks. Divers that approached the shark within 9.8 feet (3 m) affected their behavior, but after these divers have retreated, they go back to their normal behavior.
Sand Sharks in Captivity
These sharks size and relative placidity, has made them quite a popular shark species to display in a public aquarium. All the same, keeping them in captivity is not without its difficulties.
Sand sharks are highly susceptible to developing spinal deformities, with as many as two in every four captive sharks being affected. Hence, they develop a hunched appearance.
These spinal deformities have been hypothesized to correlate to both the shape of the tank and the size. If their tank is too small, these sharks have to spend more time swimming than they would in the wild, causing them to undergo stress.
Importance to Humans
Sand sharks are targets of some commercial fisheries for their fins, for meat in Japanese markets, for their oil in Australian markets, and the aquarium trade worldwide.
These sharks’ lifespan in the wild is not known. However, they live up to about 10 years or more in captivity.
Interesting Facts about Sand Sharks at a Glance
1. The Sand Sharks is a Close relative of the Great White Shark
Sand sharks and the great white shark both belong to lamniform, which is an order of sharks that share a standard look. That is to say, two dorsal fins without spines, five pairs of gill slits, lack of nictating membrane, and a relatively largemouth.
2. Their Teeth are Like Dental Fishing Hooks
When you look at a sand shark, the first thing you notice is their jagged teeth which remain visible even when they close their mouth. The design of the sand shark’s teeth is in such a way that it is perfect for puncturing the skins of small to mid-sized fish that can be slippery and hard to grab on to.
3. Sand Sharks Gulp Air to Stay Buoyant
By swallowing a mouthful of air at the sea surface, these sharks can turn their stomach into air pockets. As a result, they can keep their buoyancy level under the surface and enable them to remain motionless in the water. No other shark displays this air gulping behavior.
4. Sand Sharks Can Hunt in Groups
An American ichthyologist in 1915, Russell J.coles, was observing fish in North Carolina when he saw a school of at least 100 sand sharks surround a school of bluefish. He pointed out that by working together, Sand sharks were able to drive their victims into very shallow waters and attack them.
In other instances, a group of sand sharks near new south wales began to flare their tails about, producing cracking noises until they were able to corner some yellowtail kingfish into a tight vulnerable cluster and feed on them.
5. Sand Sharks do Well in Captivity
Sand sharks are known to thrive well in captivity. When given proper care, these sharks can live for decades in aquariums. One sand shark named bertha lived 40 years in New York aquarium in coney island before dying in 2008.
6. They do not Attack Humans Unless Provoked
Sand sharks tend to shy away when they see divers approaching, but they have been known to try to steal fish from net and spearfishers.
7. Low Reproductive rate
Sand sharks only give birth to two live pups at once and are only able to reproduce after two or three years.
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- “Sand Shark”, Wikipedia. (accessed April 13, 2020)