Ginglymostoma cirratumCat shark

Geographic Range

Nurse sharks live in warm waters. They range from the Eastern Pacific Ocean, Eastern and Western Atlantic Ocean to the Indian Ocean.

Habitat

Nurse sharks live off of sandy beaches, mud and sand flats, and from the intertidal zone on coral and rocky reefs to depths of 70 meters.

Physical Description

Nurse sharks range in length from about 75 centimeters for the short tail nurse shark to 4 meters in length for the other types of nurse sharks. The average weight of a 240 centimeter long nurse shark is 330 pounds. They are generally dark in color or have dark scattered spots along their bodies. They have broad heads, no grooves around the outer edge of their nostrils, and relatively fat or stout bodies and tails. Their anal fins are slightly behind their second dorsal fins and just in front of their caudal fins. Anal fins are absent in some families of sharks.

  • Average mass
    60280 g
    2124.41 oz
    AnAge

Reproduction

Very little is known about most shark mating rituals, and the same holds true for the Nurse shark. The Atlantic Nurse shark has been observed mating on the ocean floor. In general, the male inseminates the female with his claspers (these are located between the male's pelvic fins). During mating he turns his claspers foward and inserts one into the female and transfers his sperm. Nurse sharks can be either oviparous or ovoviparous. In oviparous organisms the eggs develop and hatch on the outside of the body. The pups, as baby sharks are called, hatch out of a leathery protective covering with the yolk attached and stay on the ocean floor until they fully mature. In ovoviparous creatures the eggs develop on the inside of the body and hatch within or immediately after extrusion by the parent. The yolk of these pups are hatched inside the uterus before the pups are developed, and they too have leathery eggs. These sharks have from 20-30 pups at a time. Nurse sharks grow about 13 centimeters in length and 2-3 kilograms a year. They do not reach sexually maturity until they are from 15 to 20 years old.

Lifespan/Longevity

Behavior

Unfortunatly, little little is know about the Nurse shark's behavior. They may have defined home ranges. In addition, their daily movements are small; one adult Nurse shark moved less than a mile in one day! Daily movements do increase with maturity, along with their body size. As with all sharks, they use their sense of smell, taste, and chemical receptors to explore their marine world.

Food Habits

Nurse sharks eat a variety of foods. Their diet includes small fishes, shrimps, octopus, sea snails, crabs, lobsters, squid, sea urchin, and corals.

Economic Importance for Humans: Positive

Nurse sharks are used in several fishing industries for bait to catch other aquatic animals. They also help control populations of several sea creatures. Scientists are also interested in these sharks because they are easy to find because of their dark color and slow moving nature. Their dark color makes them easier to spot in the water and their slow locomotion makes it easy to catch and tag these sharks, making them a relatively easy anmial to study.

Conservation Status

At present, Nurse sharks have no special conservation status. They are sought out for crab trap bait and for sport fishing, however, and their reproductive rate is relatively slow. This suggests that their populations bear watching.

Other Comments

Nurse sharks are interesting animals for of several reasons. It is not true that that all sharks need to swim in order to breath, and when they cannot for whatever reason, they die. Sharks breath primarily by using a ram-jet ventilation system, which requires that they be swimming. Some sharks, however, have a second system based on respiratory pumping of water. Nurse sharks can switch to this respiratory system when they are at rest, saving energy and the neccesity to swim to get plenty of water over their gills. This is especially important for bottom dwellers such as Nurse sharks. Nurse sharks do not attack humans, despite claims to the contrary; they are one of the most docile animals in the sea.

Contributors

Kimberly M. Scott (author), University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

References

Castro, I. J. 1983. The Sharks of North American Waters. pp. 14,21-24.

Springer, S. 1990. Discovering Sharks. pp.68-69.

Stevens, D. J. 1987. Sharks. pp.18-84.