As often as not this fishing is illegal, so what makes it worth the risk? Sharks weren’t targeted by fishers in the past — at least not in the West. Many sharks taste bad: the flesh is rich in urea and smells of ammonia. But in the Ming Dynasty in China several centuries ago, someone somehow worked out that the intensely boiled cartilage from a shark’’s fin had a nice texture; add other ingredients for flavour and you have a great soup. Fishing sharks back then was hard work and a little dangerous, so shark fin soup was not common. Eating it was a symbol of wealth and status.
Fast forward 400 years: booming economies, big boats, steel fishing wires that sharks couldn’t bite through, and a globalised fishing industry. Shark fins, which can be dried and stored for months or years, now sell for $100s per kilo, and sharks everywhere have been hammered for them. Sometimes catching sharks is done on the side, providing a little extra income to the underpaid crew of fishing boats. A dried fin is almost like hard currency. You can hang onto it, and sell to passing traders months later.
But when a reef ecosystem loses its sharks, it suffers in all sorts of ways that we are only just beginning to understand. Indeed, we barely have a baseline (a “normal”) on which to gauge that understanding.
Just a handful of remote Pacific islands (mostly uninhabited U.S. territories, like Palmyra) still have their full compliment of sharks. The sharks in these places ply the waters above the reef on a constant patrol. Surprise: These reefs have up to 4 times the total weight of fish (biomass) than do reefs without sharks. Of course the sharks themselves account for a large part of this additional biomass, but these reefs also have more of the other fish.
Why? The answer lies in complex ecology. You might imagine that if you took out the big predators, there would be less predation and more fish overall. In fact, what happens is called “mesopredator release”: The next fish down in the food chain — snappers and groupers, jacks and trevallies — increase in number. But their abundance and other behaviour changes lead to even greater predation on the smaller fish and larger invertebrates. In fact, the whole system is changed.