Certain species take over 20 years to reach breeding age. This means that the common fishing practice of taking nearly all the adult sharks from a reef practically extinguishes the shark population for the foreseeable future, perhaps for good. To make matters worse, most shark species produce few offspring when they do mate. This contrasts with other fish, which reach maturity rapidly and produce thousands of offspring in a single mating. As a consequence, shark populations have a very difficult time replenishing themselves through natural patterns of reproduction.
Sharks are top predators and keep levels of other marine life in check.
As such, the elimination of sharks is likely to disrupt the natural balance of their ecosystem. Excessive hunting of them may result in undesirable over-expansion of other marine populations, which in turn may choke marine ecosystems on which we rely for food, recreation and protection. Finally, as the top predators in their environments, sharks are relatively scarce even without being hunted. Like other animals in that role, they require a large area to find enough food to survive. This simple fact naturally limits the size of their populations.