Shark Reproduction

There hasn't been much research conducted in regards to shark reproduction, given the difficultly to obtain such data, but a great deal is known about the process.  For example,  we know that sharks are K-selected species, meaning, that they produce a small number of well-developed young, usually have a small clutch size, and are slow to mature.  We also know that shark conception generally takes place privately in the waters of the ocean and will seldom breed in captivity.

Male sharks have developed a special reproduction part - claspers.  Many people mistake the claspers for penises, thus the saying "Sharks have two penises!" Man, would female sharks be lucky if that saying was true.  The claspers are used to get the male sperm inside the female.

During shark "foreplay" the females will emit various types of chemicals into the water to attract the males.  This is because most species of sharks the males and females do not co-habitate the same area.  When a male shark is interested in mating with a female he will bite her to let her know...oh, KINKY!  No worries, the females are not hurt by this "love" bites, in fact, they have developed extra thick skin to protect them.  Some researchers believe this biting behavior also takes place during conception in order to help keep the two sharked entwined for the process to be completed.

Now, that we know all about a shark's foreplay, what about the birthing process?  Sharks are truly magically animals!  Not only have they been around for 409 million years, but they have evolved multiply reproduction/birthing methods.  There are three sexual methods in which a female can reproduce and one asexual way.

First, we will examine the sexual ways:

1)Viviparity: giving birth to live sharks
There are species of sharks, such as the blue shark, that give birth to live baby sharks, as known as pups. They only have a few at a time and they abandon them directly after birth.  From the moment the pups are born they instinctively know how to survive on their own.

2)  Oviparity: laying eggs
Other species of sharks, like the bull shark, will lay eggs in a well hidden area.  The eggs are incased in a  protective case that makes it difficult for predators to break into.  With this method of reproducing the clutch size can range from a few eggs to over 100 eggs

3) Ovoviviparity: eggs develop inside the mother
Most sharks, like the tiger shark, use this method of reproduction.  The eggs hatch inside the mother and they continue to be nourished by the yolk of the egg and some fluids from the mother.  Some species of shark's pups practice a form of cannibalism known as oophagy, which means they will eat the remaining eggs that have not hatched.

4) Asexual Reproduction: reproduction without a male
Sharks have evolved to be such specialized creatures that they not only reproduce sexually, but they can also reproduce asexually, when the environment is not conducive to sexual reproduction.  WOW!  There have been reported cases where female sharks in captivity have had no contact with a male, but become pregnant anyway.  This type of asexual reproduction is known as, parthenogenesis.  We know that parthenogenesis is possible among the female hammerheads.  This type of reproduction is extremely rare and in most cases does not occur.  However, this could be a significant reason as to why sharks have been able to survive for so many years with high population numbers.  It is speculated, however, that asexual reproduction does not take place too often in the wild, because of the abundance of males and the correct mating environment.  

References:

http://biology.about.com/b/2007/05/24/asexual-reproduction-in-sharks.htmhttp://www.marinebiodiversity.ca/shark/english/reproduction.htm

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