They have strong digestive enzymes and a specialized epithelial fold that spirals the length of the small intestine, enabling the fishes to absorb a great diversity of foods. Sharks, to a large extent, are scavengers, eating injured fishes, carrion, garbage, and other waste from ships as well as animals such as seals, turtles, birds, whales, crabs, and a wide range of fishes. Males can be identified by claspers, which are extensions of the pelvic fins that serve as copulatory organs. The sand tiger shark, for example, bears only two young at a time. Fertilization takes place internally, the male inserting one of its claspers into the female.
Most sharks are ovoviviparous, hatching the eggs within the female and bearing live young.
Embryonic development takes more than six months, and in the Atlantic spiny dogfish it takes close to two years. The young are frequently born in protected inshore areas away from the males. Seeing, although less acute, allows the shark to catch dim movements of shadow and light in dark waters as it approaches its prey. Sharks are particularly sensitive to sounds of low frequency and have fine directional hearing. Organs along their lateral lines and on the snout enable sharks to pick up weak electrical stimuli from the muscle contractions of bony fish.