A fisherman cleans a small hammerhead shark at Boca del Asadero, state of Nayarit, Mexico.

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Threats to Sharks

­Despite their superior physiology and hunting skills, many shark species are now threatened with extinction due to human fishing. The main threats to sharks are over-fishing and accidental bycatch. In many parts of the world, sharks are in very high demand, for their meat, skin and cartilage, which is used in several medicines. These shark products sell at very high prices, making them an attractive catch to fishermen.

­Sharks mate only rarely and have a relatively small number of shark pups at a time. Consequently, they can't replenish their population quickly. Sharks also have fairly long lifespans -- on average, sharks live 25 to 30 years. According to Andy Dehart, Director of Biological Programs at the National Aquarium and shark expert for Discovery Communications, sharks can live up to 60 years, with the spiny dogfish reaching 70 to 100 years. If left alone, a female will mate many times in its life. With this reproductive pattern, the death of every single shark obviously has a significant effect on the shark population­. ­

Over-fishing is actually a problem for both sharks and humans. If humans kill too many sharks in a given amount of time, the population will dw­indle and they won't be able to catch many sharks in the future. The only way to maintain profitable shark fishing over time is to allow sharks to continue to reproduce, which means decreasing shark fishing significantly. Sharks are also killed accidentally, primarily by long lines used to catch other fish. Researchers suggest we must ban certain fishing methods, or some shark species will die out at some point in the near future.

­­One major obstacle to conservation efforts is our ignorance about sharks. We still don't fully understand their behavior, their breeding habits or their migration patterns. For most shark species, we don't even have an idea of their population size. This makes it very difficult to organize effective conservation methods since we can't accurately calculate safe fishing restrictions.

Sharks have persevered for hundreds of millions of years, while thousands of other animals have come and gone. When you consider this incredible history, and the unique physiological characteristics found in sharks, it's clear that it would be a great tragedy to lose any shark species. They are among the most remarkable animals on earth, and there is still so much we don't know about them.

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