Nurse Shark

Sometimes called the couch potatoes of the sea, nurse sharks are large, peaceful fish. They slowly drift along the bottom of the ocean in shallow water, sucking up food as they go. They hunt alone at night but return to the same comfortable resting place during the day to doze. Although their habitat is alongside humans, these fish are rarely harmful; they will only bite if startled or provoked. These gentle sharks are quite comfortable in zoo aquariums and can live up to 25 years in captivity.

5 Nurse Shark facts

• Unlike many other shark species, the nurse shark uses the buccal pumping method to breathe. This involves the use of their oral muscles to pull water into their mouths to oxygenate their gills. It allows them to stay still and even sleep.
• These sharks don’t pose any threat to humans unless they are disturbed. In fact, many people swim right by these sharks without ever knowing they were there.
• When a school of nurse sharks finds a comfortable resting place, they return there each day after hunting. They do not migrate, as do many other fish species.
• They use their pectoral fin to “walk” across the ocean floor. Females sometimes bury their pectoral fins in the sand to avoid the mating advances of males.
• Rather than chasing prey and catching it with chomping teeth, this species swims above the ocean floor and sucks up food like a vacuum cleaner. After sucking their food into their mouths, they use rows of serrated teeth to crush it before swallowing.

Scientific name

The nurse shark is in the Ginglymostomatidae family and the Chondrichthyes class. Its scientific name, Ginglymostoma cirratum, is a mix of Greek and Latin and means “curled, hinged mouth.” This name is rather fitting because this shark always looks like he’s puckering up. Since they prefer to hover over the ocean floor, scientists believe its name came from the Old English word “hurse.” This means sea-floor shark.

Evolution Of the Species

All sharks evolved from the Acanthodian, a group of spiny fish. These fish were first around over 400 million years ago, during the Paleozoic era. This group of fish then divided into the two main groups of fish that we now have today. These include cartilaginous fish (Chondrichthyes), of which sharks are part, and bony fish (Osteichthyes), which include salmon.

Types Of Nurse Sharks

The following nurse sharks should not be confused with the grey nurse shark, which is a different species (Carcharias taurus).

• Tawny nurse shark (Nebrius ferrugineus)
• Shorttail nurse shark (Pseudoginglymostoma brevicaudatum)
• Atlantic nurse shark (G. cirratum)

Appearance

The nurse shark has a wide body and a short snout with a small, rectangular mouth. They have two sensory organs called barbels that grow down from their upper lip. These barbels help them find small fish and crabs hiding in the sand.

This species of shark looks a bit different than many of its more dangerous cousins. Their thick skin is smoother than that of most other sharks, and their dorsal fin is round rather than sharp. Their color sets them apart from the others as well — they are tawny brown rather than grey.

These sharks grow to about 7.5 to 9 feet long and weigh between 150 and 300 pounds. The largest nurse shark on record is 14 feet long, more than two times longer than the average man’s height. They also have long tails, which can make up about a quarter of their total length.

Behavior

The nurse shark is a solitary, nocturnal hunter. However, during the day, it will probably be resting in a pile of other similarly sized sharks. These sharks don’t migrate; when they finish hunting for the night, they return to their favorite area to rest.

Habitat

Nurse sharks like warm, shallow water and live all across the eastern part of the Pacific Ocean and the western part of the Atlantic Ocean. They live close to human activity and, while they are not usually aggressive, can bite in self-defense if humans encroach on their territory.

Population

The abundance of nurse shark populations worldwide was estimated using an analysis of distance sampling. Their current numbers range from 3,858 to 14,375. However, their numbers are low in certain areas due to previous overfishing for their skin and oil. Although nurse sharks are not routinely hunted on a global scale, they are still regionally targeted for their fins, meat, and skin. The species is listed as Vulnerable by the IUCN, and populations are declining in some areas. The IUCN Red List globally assesses the nurse shark as Vulnerable.

Diet

A nurse shark’s mouth possesses rows of tiny, serrated teeth that can crush hard-shelled crustaceans and snails. Small fish, shellfish, shrimp, and squid are some of the nurse shark’s favorite foods, though they will also eat algae and coral from time to time. Since they hunt at night, they eat fish that are resting.

Predators And Threats

The nurse shark doesn’t have any specific predators, but it can make an easy meal for larger fish such as tiger sharks or lemon sharks. The nurse shark is classified as Vulnerable by the IUCN, meaning it is considered a threatened species.

Reproduction, Babies, And Lifespan

When a nurse shark wants to mate, the male will bite the female’s pectoral fin to hold her in place for the mating process. This species is unique in its reproductive process compared to other sharks because more than one male can fertilize the same litter.

This species of shark is ovoviviparous, meaning that the female carries the fertilized eggs inside her to incubate. When the six-month incubation period comes to an end, she gives birth to a litter of about 25 live pups. These pups are roughly 8 to 12 inches in length when they are born. After giving birth, it takes the female 18 months to produce eggs and go through the reproductive cycle again.

In Zoos

Nurse sharks do well in captivity, possibly because they are less active than other shark species. Since they don’t need to stay swimming to breathe, they are less bothered by smaller living spaces than their more active cousins. The average lifespan for a nurse shark in captivity is up to 25 years.

You can find them at Point Defiance Zoo & Aquarium in Tacoma, Washington; Omaha’s Henry Doorly’s Zoo & Aquarium in Omaha, Nebraska; and the National Aquarium in Baltimore, Maryland, to name just a few.