NURSE SHARK
- Friendly Fins
- Dec 12, 2024
- 5 min read
Updated: Mar 7
Why learn about the nurse shark?
“Shark to whom? More than sharks, we are the elegant cats of the coral reef!”
The origin of its name Ginglymostoma cirratum seems to be a mix between Greek and Latin, called so because of the hinge shape (cirratum) of its mouth. The English term “nurse shark” however derives from an archaic word “nusse” which means “cat fish” i.e. cat shark.
How do we recognize the nurse shark?
It reaches dimensions of up to 4 and a half meters and weighs 150 kg, the males are as large as the females.
Its color is very recognizable: the adult varies from a yellowish to a very light brown to a darker one, also depending on the color of the seabed. The young ones up to 60 cm have small black spots all over the body with a lighter outline. As they grow, these spots will become less and less evident until they disappear.
The mouth is much further forward than the eyes and on the sides it has very obvious growths called “barbels”.
“We need them for so many things!”
The tail is very long and can reach a quarter of its body.
“We often forget it outside the caves where we sleep, we are not good at playing hide and seek!”
The light eyes are very small and located laterally between the mouth and gill slits;
“We can see you from up to 10m away!”
The skin is made up of countless tiny scales (placoid scales) made up of dentine and very similar to our teeth! These scales, in the nurse shark, take on different shades of color from light yellow to black, creating beautiful shades on the skin. Their function is to ensure effective hydrodynamics,
“If you are close enough to us you will even be able to see them with the naked eye.”
Where does the nurse shark live?
The nurse shark lives in the coral reefs of the tropical coastal waters of the Atlantic, Indian and Pacific oceans. In this environment it finds everything it needs, starting from food and rest! It does not migrate or move away for great distances from the coral reef. It is not a pelagic shark but rather sedentary…
Precisely because of its low daily activity, it has developed the ability to actively pump water into its mouth and then let it out through its gills, allowing it to breathe comfortably from its hiding place, without the need to swim. Although it is a solitary shark, large groups are often found in some cave or crevice huddled together until nightfall, when these splendid animals come to life and start hunting.
“The barrier life destroys us! In fact, we love to sleep all day in the shade… We are very creatures of habit, so, after the night hunt, we usually return to the usual place”.
What and how does the nurse shark eat?
Their favorite buffet consists of small fish, crustaceans such as lobsters and crabs, and molluscs such as octopuses and clams.
“We are quite lazy, so rather than hunting, we try to catch the slow-moving animals around us!”
The effectiveness of nurse shark hunting
Its teeth are not pointed like those of other sharks but rather rounded with a very wide base and all close together to create a sort of large plate that gives strength to the bite. It also changes them every 10-14 days when it is actively eating and every month or two when it is less active.
The ability to use the mouth as a suction cup to suck up prey hidden inside their burrows. The small mouth is compensated by a large throat that allows this suction.
Two fleshy barbels located ventrally just above the mouth, this makes them the reef cats! Excellent movement receptors that help the shark to detect any animals hidden on the bottom.
A very developed sense of smell that allows it to understand what type of prey is around it, strictly dependent on environmental conditions such as currents, waves and obviously the distance from the prey.
Electroreception is typical of all sharks, thanks to special ampoules containing electroconductive gelatin (Ampullae of Lorenzini) located on the snout, the shark is able to perceive the movements of the animals around it. This special sense has a range of action of less than 1 meter, which means that it is used strictly to capture the prey by giving the exact position in which it is located.
Hearing capable of picking up low-frequency sounds for many kilometers.
The Life of the Nurse Shark
The average lifespan of a nurse shark in its habitat is 25 years.
It reaches sexual maturity between 15 and 20 years of age when males reach 2 metres and females 2.40 metres.
Reproduction occurs between June and July for about 2 weeks, always in the same places and at night.
Males have two penises: the claspers, like all other sharks, become fully developed and calcified when they reach sexual maturity.
Females reproduce once every 18 months.
Gestation lasts six months, with the baby giving birth in shallow areas, among vegetation or in the coral reef, in places as sheltered as possible from predators..
It is born measuring 30 cm together with 20-30 other fully formed siblings who will not receive any parental care from the mother (they are not looked after).
The nurse shark is ovoviviparous, meaning it gives birth to fully formed young and the eggs hatch inside the mother's body after the young have eaten all of her food.
A particular polygamy: Polygynandrus
During mating, the male wraps himself around the female's body, biting her pectoral fin and trying to immobilize her as much as possible. So far, everything is normal for a shark! So the sexual life of a nurse shark is rather resolute, in fact during the reproductive season, both males and females mate with different partners (Polygynandrus, that is, many females and many males)
“This strategy gave us a significant genetic advantage and greater success in fertilizing the eggs, having more sperm donors available at different times.”
The Nurse Shark's Enemies
In general, all sharks have enemies because they take a long time to grow, and are at risk of becoming prey to larger sharks. An adult nurse shark, on the other hand, could be attacked, although rarely, by larger sharks such as the lemon shark, hammerhead shark, tiger shark and bull shark.
Besides its cousins, its worst enemy is man. Like all other sharks, the nurse shark has also suffered a huge decline over time due to fishing, but unlike other sharks, it is not considered a fishing trophy but hunted by local fishermen both because of its particular very resistant and flexible skin (sold as leather) and for its meat. Unfortunately, it is a very easy prey as it is a peaceful animal and very curious about us. Very often it is approached to boats or ports with food and this has made it too accustomed to man, leading it to easy fishing.
Now Friendly Fins ready with mask and fins!
Let's find out how to get in touch with them...
Comments