Sharks are often known as one of the fiercest predators in the ocean. Yet they are also one of the most threatened marine species—largely because they are hunted by humans for their highly valuable fins. How do we know they are being threatened?

Traditionally, researchers have estimated the population and diversity of sharks using two methods. One is by sending divers into the water to count the number of sharks and record which species they see. Another is to set up baited cameras in different locations to record the sharks that come near. When fewer species of sharks are examined using these methods, we conclude that there is a decrease in diversity and an increase in what’s called “dark diversity”.