By Kimberly M. Scott
Geographic Range
Nurse sharks live in warm waters. They range from the Eastern Pacific Ocean, Eastern and Western Atlantic Ocean to the Indian Ocean.
Biogeographic Regions:
indian ocean (native 
); atlantic ocean (native ); pacific ocean (native ).
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.
Some key physical features:
bilateral symmetry .
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.
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.
Key behaviors:
natatorial ; motile .
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.
