One-Quarter of Sharks and Rays Face Extinction

[LeftyMom]

3. Part of the problem is that they're slow to reach maturity and mostly reproduce slowly.

Apologies, this is a slightly complicated explanation because sharks have several different methods of reproduction:

Unlike bony fish who pop out some eggs and spray some semen on them and take off, sharks have internal reproduction and give birth to significantly fewer young. Some of them give birth much like mammals do, with one or two young living off of a placenta and then being born when they're fully equipped to feed and care for themselves- white sharks are a good example of this. Sharks don't parent but they do appear to have a biological mechanism that prevents the mother from feeling hunger until the young have had time to get away. Other shark species grow their young internally for some period and then release rubbery egg cases that develop the rest of the way on their own- these are the most fecund species but many of the egg cases will be eaten before they develop. The final group split the difference between the two- the young develop internally but are fed by an egg sac. Some of these species engage in intrauterine cannibalism, and the fastest developing embryo on each side of the mother's divided uterus will eat it's siblings, so an initial litter of dozens will result in two pups, no more and no less.

So long story short, with variations for different types of reproduction most shark species take a very long time to become sexually mature and reproduce slowly: usually only one or two pups every other year for live-bearing species.