Grey Nurse Shark (also known as Sand Tiger or Ragged-Tooth Shark)
The Grey Nurse shark (Carcharias taurus), or ”Raggies,” goes by many names around the world. In the USA they are referred to as Sand Tiger Sharks, and in both Australia and the UK they are called Grey Nurse Sharks. But the South African name Spotted Ragged-tooth shark is by far the most descriptive name for there appearance. For ease we will refer to them as 'Raggies'.
Although its latin name 'Carcharias taurus' roughly translates to “Bull shark” and at some places called Sand Tiger shark, its closest relative is actually the Great White shark (Carcharodon carcharias).
Anatomy and appearance of the Grey Nurse shark
Adult Raggies range from 2 meters to 3.2 meters in length and can weigh between 91 to 159 kilograms. They have a sharp, pointy head with a stout and bulky body. The Raggies’ eyes are relatively small and lack eyelids. Their underside is pale and their back is grey-brown with reddish-brown spots. An interesting feature of this species is that their second dorsal fin is almost as large as the first dorsal fin. Unlike fish species that rely on swim bladders, Raggies surface to gulp air, which fills their stomachs. This unique behavior allows them to stay neutrally buoyant, in the water, with little effort.
Habitat of Grey Nurse sharks
Raggies inhabit subtropical and temperate waters worldwide. They typically inhabit the continental shelf, from sandy shorelines and submerged reefs. They can be found in the waters of the Atlantic, Pacific and Indian Oceans, along with the Mediterranean and Adriatic Seas. Raggies roam the epipelagic and mesopelagic regions of the ocean, sandy coastal waters, estuaries, shallow bays, and rocky or tropical reefs, at depths of up to 190 meters.
Grey Nurse shark diet
Raggies are nocturnal feeders that use stealth to hunt their prey. They feed on bony fish, crustaceans, squid, skates and other smaller sharks. During the day, they take shelter near rocks, overhangs, caves and reefs often at relatively shallow depths (<20 m), hovering just above the bottom in large sandy gutters and caves. However, at night they leave their shelter and hunt over the ocean bottom, often far from their shelter.
Population of Grey Nurse sharks
Mating among ragged tooth sharks is a dramatic affair. Females often suffer inadvertent injuries while mating since the male needs to grasp the female with his jagged teeth while swimming alongside her. Raggies are ovoviviparous, which means the embryo hatches from the egg within the shark. Newly-hatched sharks feed on any other embryos and eggs present until they are large enough to face the outside world. This is a reproductive strategy known as intrauterine cannibalism i.e. "embryophagy" or, more colorfully, adelphophagy - literally "eating one's brother". For this reason, the female continues to produce eggs even while pregnant. Baby Raggies are called pups, and an adult female usually gives birth to one or two pups after a gestation period of about a nine to twelve months. Once they leave the womb, the pups are entirely independent of their mother.
Raggies are born about 1 m in length. During the first year, they grow about 27 cm to reach 1.3 m. After that, the growth rate decreases by about 2.5 cm each year until it stabilizes at about 7 cm/y. Males reach sexual maturity at an age of five to seven years and approximately 1.9 m in length. Females reach maturity when approximately 2.2 m long at about seven to ten years of age. They are normally not expected to reach lengths much longer than 3 m.
Conservation of Grey Nurse sharks
Although Raggies are a fully protected, they have been assessed by IUCN Red List as 'CRITICALLY ENDANGERED' in 2020. There are several factors contributing to the decline in the Raggie population. One such reason is that Raggies reproduce at an unusually low rate, due to the fact that they don’t have more than two pups at a time and because they breed only every second or third year. Another reason is that they are a highly prized food item in the northwest Pacific waters along with the coastal areas of Ghana, India and Pakistan. They are most commonly caught with fishing lines and occasionally caught by fishing trawlers. Raggies are also prized by aquariums throughout the world because of their docile and hardy nature.
Relationship between Grey Nurse sharks and humans
Raggies are often unfairly associated with being vicious or deadly. This can be attributed to their relatively large size, beady eyes, hump-backed appearance and needle-like teeth that point outward from their jaws. The teeth of the Raggies are used only to secure their next meal before swallowing it whole. As a result, the average sized person is much too large for a Raggie to be interested in consuming. Despite their menacing appearance they are in fact docile, slow-moving creatures, and are quite easy going around humans.
Written by Izabella Englund (Internship Student from Crystal Divers South Africa - Shark Guardian Dive Center)
Comments