Nurse Shark: The Laziest Shark You Will Ever Meet
Everything you need to know about the laziest shark you will ever meet: Nurse Shark
Nurse shark are known for spending a lot of time resting in the ocean floor. In fact, they are so lazy, they don’t even migrate to warmer waters when its cold. They live in reefs of tropical and temperate waters of Atlantic and Pacific Oceans.
These fish are the delight of many scuba divers, being an important part of ecotourism in some regions. However, fisheries and climate change have contributed to the decline of nurse shark populations, putting them in a vulnerable situation. Nurse shark are known as the lazy shark for spending a lot of time resting in the ocean floor.
Where does the name come from?
There are some theories regarding the origin of nurse shark’s name. It is suggested that the sucking sound that this fish makes when it hunts, is similar to the sound of a nursing baby. Another theory is that the name comes from the archaic word nusse, or cat shark. However, the most accepted theory is that it comes from the word hurse, which means sea-floor shark in Old English.
Biology and behaviors
Nurse shark sizes range between 7.5 and 9.75 feet, and they can weight up to 330 pounds. Unlike other sharks, they are usually brown, but yellowish and grey nurse sharks have also been reported. Young specimens have black dots covering them.
These fish have round heads and small eyes. Like their relative whale shark, they have barbels containing taste buds, two dorsal fins and five sets of gill slits. Their jaws are strong and filled with thousands of backward-curving teeth. During summer, a fresh row of teeth arises every 10 to 20 days, and in winter it occurs every 50 to 70 days, while old teeth fall out.
Nurse sharks are nocturnal animals. During the day they usually rest near the sea floor. Even though they are not very social animals, nurse sharks like to pile up on top of each other while resting. Groups of two to forty fish have been reported. Interestingly, they are able to use their pectoral fins to “walk” across the ocean floor instead of swimming.
Where do they live?
Nurse sharks are usually found in the shallow waters of the eastern Pacific Ocean, and the eastern and western Atlantic Ocean. They live on coral and rocky reefs of tropical and temperate regions.
The majority of nurse sharks remain in the same area all year. However, partial migration is reported, as some fish migrate between mating seasons.
Reproduction and life cycle
Male nurse sharks bite one of the female’s pectoral fins and drag them to deeper waters in order to mate. On their turn, females can mate with different males.
They are ovoviviparous which means that embryos develop inside eggs that are retained within the mother’s body. There is no placenta and the embryos are nourished through a yolk sac that is absorbed during development.
Gestation period lasts for five to six months. Females are able to give birth between 20 to 40 juveniles from up to six different males. Nurse sharks can live up to 25 years.
When male nurse sharks want to mate, they bite the female on her pectoral fin to hold her into position.
What do they eat? What eats them?
Nurse sharks feed on shrimp, fish, squid, and shellfish. They usually hunt on the ocean floor, and use their barbels to search for prey. A cavity present in nurse sharks throat enables them to suck prey into their mouths, where it is further crushed by the powerful jaws and teeth.
These fish don’t have many natural predators. But, occasionally, nurse shark remains are found in the stomach of lemon shark and tiger shark. Besides, there are reports of attacks by bull shark and hammerhead sharks too.
Are nurse sharks danger to humans?
Scuba divers in Florida, for example, frequently come across with nurse sharks. In general, they are harmless to humans. However, they might attack when they feel threatened or when they mistake us for food.
Ecotourism is responsible for an increase in the number of attacks in recent years. In fact, there are reports of nurse shark attacks, that usually result from human provocation. In extreme cases, the fish latches and won’t let go, and surgical instruments might be needed to open the jaw. Even though they are shy, scuba divers are advised to not approach them.
Nurse Shark are harmless to humans unless they feel threatened.
Main threats and conservation status
The main threats against nurse shark include the capture in coastal fisheries, spearfishing and trading for ornamental purposes. In some countries, such as Brazil and Venezuela, they are consumed by fishermen.
They are also captured for their skin in some parts of the Caribbean, to produce high quality leather. In Colombia and Panama nurse sharks are actively targeted by artisanal fisheries, for their fins, meat and skin.
In addition, juveniles are captured for aquarium trade. In USA, they are sometimes by-caught, but are released alive and survivorship rate is high. Climate change is also another concern due to the destruction of coral reefs where nurse sharks inhabit.
Because of this, unfortunately, some populations are decreasing. In some regions of Brazil, for example, nurse sharks are locally extinct. Additionally, Short-tail nurse shark is classified as critically endangered, and Tawny nurse shark is considered vulnerable by IUCN. Currently, there are no conservation measures for these species.
What can be done to help nurse shark populations?
IUCN recommends the establishment of habitat protection, regulation of spear-fishing activity and marine ornamental fish trade, and bycatch control.
For some species, data are not sufficient to evaluate populations trend. Therefore, research is needed, especially regarding populations size and distribution.
In addition, more evidence is required about life history, ecology, threats and harvest of nurse sharks. Monitoring of population trends is essential for species conservation.