How severe are shark population decreases, and how do we know?

John Shepherd once said that counting fish is like counting trees, except that fish move and you can’t see them because they’re underwater. This is true with sharks as well. It’s basically impossible to know how many sharks there are. Fortunately, a variety of methods exist that can be used to determine population trends. In other words, even if we can’t know how many sharks there are, we can tell if there are more or less than there used to be. Presented here are brief descriptions of some of these methods and the conclusions of major shark conservation studies that used them. Though no one method is perfect, the fact that so many different methods have such similar conclusions is quite telling.

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