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BiologyDuring the day the nurse shark is a sluggish animal, spending most of its time resting on sandy bottoms, or in crevices in rocks and coral reefs. Often several nurse sharks may congregate when resting, sometimes even piling on top of one another (2). At night however, the nurse shark actively roams the sea bottom and reef for prey. It feeds on bottom invertebrates such as spiny lobsters, shrimps, crabs, sea urchins, squid and octopi (2). It is also feeds on fish, its nocturnal nature enabling it to prey on resting fish that would be too active during the day to capture (2). The nurse shark's small mouth and large pharynx enable it to feed by a unique suction method, effectively making the nurse shark the 'hoover' of the ocean floor. By cupping its mouth over a hole or crevice and expanding its throat, it creates a vacuum that sucks prey out of their hiding (4). This suction-feeding is also useful for extracting snails from their shells (2), and it will dig in sand to root out prey sensed by its fleshy barbels (2). The nurse shark is one of few sharks in which courtship behaviour is relatively well known (4). The male swims alongside the female, grabs one of the pectoral fins in his mouth, rolls her over and they mate (4). A large number of males will often try to mate with a single female, and females often bear numerous bite-scars and bruises received during mating attempts. It is therefore not surprising that females frequently try to avoid males by swimming in very shallow water, where they can bury their pectoral fins in the sand (5). Nurse sharks are ovoviviparous (2), a method of reproduction whereby the young develop inside a weakly-formed egg shell within the mother, receiving nourishment from their yolk sac, for five to six months (2). The females move to shallow seagrass beds and coral reefs to give birth to 20 to 30 pups in late spring and summer (2). Like many sharks the nurse shark is slow growing, with males not reaching maturity until 10 to 15 years of age, and females 15 to 20 years (2).