Introduction to hatching shark eggs: The eggs of oviparous sharks are large and often have thick egg sheaths that allow them to attach to rocks or seaweed to resist predators. Shark eggs are mostly wide rectangles, with a short, hollow horn at each corner outside the egg sheath, through which seawater can enter to provide oxygen to the eggs. Depending on the species, the baby sharks will hatch within a few days or weeks, at which point the larger shark will leave the young to survive on their own. The picture shows shark eggs hatching in an aquarium.