Resulting embryos usually reach a quite large size at birth. Most sharks have independent gestation periods and ovarian cycles, that is, they do not begin egg development until after giving birth. Thus, including gestation, they give birth about every two years. Other species, such as hammerheads and sharpnose sharks, concurrently gestate and develop eggs, thus they can mate immediately after giving birth, producing yearly litters. It concurrently develops eggs, so it produces litters every two years.
Most sharks have specific mating areas.
If these can be identified by fishers, they easily can be severely overfished during mating season. Nursery areas are located in inshore shallows or estuaries for most commercial species. Nursery areas offer young sharks abundant supplies of food and some protection from their major natural predators, larger sharks. Larger individuals of many shark species are found predominantly in deeper offshore waters, leaving shallower depths to the young. Many inshore nursery areas are threatened by human development, pollution, and commercial and sport fishing.