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It’s not just corals — sharks and other big reef predators are also vanishing

A gray reef shark swims inside a tank during a presentation of European Shark Week in a Madrid zoo aquarium in 2011. (Andrea Comas/Reuters)

The coral reef formations of the deep sea are huge rocklike structures with thousands of nooks and crannies that little fish call home. John Bruno, a University of North Carolina marine biologist, has seen them up close while diving.

But a trip to a reef isn’t satisfying if big predators — sharks, barracuda, grouper and such — aren’t lurking there, looking to snack on some pretty little thing that ventures from its hole. Bruno says he hasn’t been satisfied in a long time, and his newest research, published Wednesday, shows why: Up to 90 percent of reef predators have been removed from the Caribbean because of overfishing.

“Reefs are largely devoid of anything big,” he said during an interview, in a tone bordering on sad. “Just like the forests, there’s nothing big … just squirrels, a few deer here and there. Bear has all been hunted out.”

The consequences are twofold, explained Bruno, a professor at UNC Chapel Hill.

The absence of apex predators, and even smaller predators like snapper, can throw an ecosystem out of whack. Consider the removal of wolves from forests and sea stars from the Pacific Ocean off California, Oregon and Washington.

Without wolves, deer run amok, eating areas of the forest bare, trampling grasses and gnawing on trees, all of which ruins the habitat of smaller animals. In the Pacific, a wasting disease that has devastated sea stars in turn has left the sea urchins they preyed on to multiply and gobble kelp, removing hiding places for small fish and eventually causing the urchins to starve.

Another problem is that sharks are worth a lot to Caribbean islands because they’re what snorkelers and divers want to see, far more than candy-colored tropical fish.

“A live shark is worth over a million dollars in tourism revenue over its lifespan because sharks live for decades and thousands of people will travel and dive just to see them up close,” said Abel Valdivia, a study co-author who was a UNC graduate student during the research. He now works at the Center for Biological Diversity in Oakland.

Valdivia and Bruno, along with a third researcher, Courtney Cox, visited 39 reefs off Belize, Mexico, Cuba, the Bahamas and Florida — some protected in reserves, most not — to determine how many fish had vanished. Long story short, they counted predators as the predators circled them.

They compared the numbers counted at pristine reefs that were full of life to the typical reef. That’s how they arrived at the conclusion that 90 percent of predatory fish are gone, more than likely from overfishing. Bruno said they might have over-counted sharks, especially, because they often circle back around and can easily be counted twice.

“Right now, there are less than 1 percent of diverse reefs, not many of them across the Caribbean,” Bruno said.

The study, published in the journal Science Advances, took three years of searching and traveling to reefs in the Caribbean. The most diverse and spectacular reef was off Cuba, in a reserve called Jardines de la Reina. 

Jardines thrives, Bruno said, essentially because anyone with a boat good enough to reach the area would rather use it to escape the island altogether to reach Florida. Most fishing is done off the coast of the main island, by people floating in tubes with hooks dangling in the water.

After being disappointed by reefs in Mexico, the Bahamas and other areas, Jardines “totally opened my eyes to what natural was in the Caribbean,” Bruno said.

The silver lining is that, if left alone, reefs with features small fish like can come back to life, attracting predators in search of food. Of course, fishermen would also have to stay away from grouper, a favorite restaurant fish. Taking reef sharks would also have to be outlawed.

“Some features have a surprisingly large effect on how many predators a reef can support,” said Cox, a former UNC doctoral student who now works at the National Museum of Natural History in Washington. She said the Columbia Reef in a fishery off Cozumel, Mexico, could support 10 times its current level of predatory fish if protected.

Fishermen are outsmarting themselves, the scientists said. They love to chase breeding aggregations, when huge groups of fish meet to spawn. “Fishermen know where they are … just snatch them all up,” Bruno said. “Obviously, that’s a totally unsustainable way to fish. You’re eating all the brood stock and next year there won’t be any babies.”

Not for humans or predators.

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