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How do sharks give birth to babies?

How do sharks give birth to babies?

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  • WYN
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    1 decade ago
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    REPRODUCTION

    The sex of a shark can be easily determined. The males have modified pelvic fins which have become a pair of claspers. The name is somewhat misleading as they are not used to hold on to the female, but fulfill the role the mammalian penis.

    Mating has rarely been observed in sharks. The smaller catsharks often mate with the male curling around the female. In less flexible species the two sharks swim parallel to each other while the male inserts a clasper into the female's oviduct. Females in many of the larger species have bite marks that appear to be a result of a male grasping them to maintain position during mating. The bite marks may also come from courtship behaviour: the male may bite the female to show his interest. In some species, females have evolved thicker skin to withstand these bites.

    Sharks have a different reproductive strategy than most fishes. Instead of producing huge numbers of eggs and fry (99.9% of which never reach sexual maturity in fishes which use this strategy), sharks normally produce around a dozen pups (blue sharks have been recorded as producing 135 and some species produce as few as two).[14] These pups are either protected by egg cases or born live. No shark species are known to provide post-natal parental protection for their young, but females have a hormone that is released into their blood during the pupping season that apparently keeps them from feeding on their young.

    There are three ways in which shark pups are born:

    1. Oviparity - Some sharks lay EGGS. In most of these species, the developing embryo is protected by an egg case with the consistency of leather. Sometimes these cases are corkscrewed into crevices for protection. The mermaid's purse, found washed-up on beaches, is an empty egg case. Oviparous sharks include the horn shark, catshark, Port Jackson shark, and swellshark.

    2. Viviparity - These sharks maintain a placental link to the developing young, more analogous to mammalian gestation than that of other fishes. The young are born ALIVE AND FULLY FUNCTIONAL. Hammerheads, the requiem sharks (such as the bull and tiger sharks), the basking shark and the smooth dogfish fall into this category. Dogfish have the longest known gestation period of any shark, at 18 to 24 months. Basking sharks and frilled sharks are likely to have even longer gestation periods, but accurate data is lacking.

    3. Ovoviviparity - Most sharks utilize this method. The young are nourished by the yolk of their egg and by fluids secreted by glands in the walls of the oviduct. The eggs hatch within the oviduct, and the young continue to be nourished by the remnants of the yolk and the oviduct's fluids. As in viviparity, the young are born alive and fully functional. Some species practice oophagy, where the first embryos to hatch eat the remaining eggs in the oviduct. This practice is believed to be present in all lamniforme sharks, while the developing pups of the grey nurse shark take this a stage further and consume other developing embryos (intrauterine cannibalism). The survival strategy for the species that are ovoviviparous is that the young are able to grow to a comparatively larger size before being born. The whale shark is now considered to be in this category after long having been classified as oviparous. Whale shark eggs found are now thought to have been aborted. Most ovoviviparous sharks give birth in sheltered areas, including bays, river mouths and shallow reefs. They choose such areas because of the protection from predators (mainly other sharks) and the abundance of food.

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