Why Sharks Are Declining Worldwide
If you think marine biologists get blasé about the remote places we’ve been and the wonderful animals we’ve seen, think again. I’ve visited countless uninhabited islands and spent hours underwater with incredible creatures such as turtles, manta rays and giant groupers — and I love talking about them. But even among the pros, just like the public, sharks are a special cause for fascination and discussion.
These days, sharks have been decimated worldwide and annihilated in many places. You could dive for weeks on end in the Caribbean or the Asian Islands and not see one. A good sighting would be a glimpse of little reef shark racing off into the blue, terrified. (Of course, we could join the shark-feeding tourism extravaganzas, but marine biologists tend to rank these efforts alongside zoos — good fun, good even for public education, but not the real thing.)
Regardless, a good view of a shark instills immediate respect. They take your breath away, especially up close. These are the ocean’s great predators, honed by millions of years of evolution: perfect in their way. Their steel-eyed gaze gives you a sense of cold rationality as they cruise, almost effortlessly past you. But these “apex predators” aren’t just awe-inspiring; they are an integral part of a functioning ocean.
My shark sightings have been mostly in the remote reefs of the Seychelles and the Chagos Archipelago. The Chagos used to be thick with sharks in the 70s — scientists on expeditions then worked with armed guards, an extra buddy to keep an eye out and a large stick to hand if the sharks got too inquisitive. By the time I got there in the ’90s, though, you only saw one or two sharks per dive, and they weren’t so inquisitive. But that’s good compared to most coral reefs where you might just see one shark every 10, 50 or 100 dives. Even in the remote reefs of the central Indian Ocean, sharks have been “mined” to miniscule populations.
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.
As a sad addendum, in fact there are barely any reefs where even mesopredator release can take place, for these mesopredators are popular targets, too. Even on remote reefs, such large fish are prime targets for East Asian restaurants — taken alive so that diners chose them fresh from the aquarium, at sometimes phenomenal prices.
In reality, we barely have a natural reef left to study. We have a plethora of stories about how things can go wrong, and just a handful of hopeful places where we can catch a glimpse of how things once were.
Ecology is complex, and the solutions are too. Of course, strict protection of sharks and mesopredators might be part of the solution, and no-take reserves can be really valuable; but lots of this fishing is already illegal. Punitive measures on fishers might also have a place, but not on the desperately poor fishers for whom the cash incentive will still perhaps be worth the risk. There is a market driving phenomenal prices and illegal activities, and cracking that requires education of a broader public, buyers, sellers and politicians who can change trading regulations. We have the solutions and efforts are underway on multiple fronts — but not enough, not yet.
(Image: Blacktip shark at Palmyra Atoll. Image credit: Laura M. Beauregard – USFWS/Flickr through a Creative Commons license.)
Mark Spalding is a marine scientist with The Nature Conservancy. Read more of his blog posts here.
By Mark Spalding, The Nature Conservancy