Tropical coral reefs are fertile fishing grounds for some 200 million small-scale fishers around the world. 

But many of these reefs are in decline. Tim McClanahan with the Wildlife Conservation Society has followed the catch from one coastal fishing community in Kenya for more than a decade. 

“It was going down every year. It was just one of those beautiful exponential decay curves,” he says.

The question was, what could they do to stop that decline before it crashed the whole reef ecosystem?

Such a crash would not just be bad for the fish. The fishers who make their livelihoods from the reef would suffer as well. 

Since no one owns the oceans, most countries put fisheries management in the hands of the central government. But it’s a complicated business, with a huge number of fishers, catching many different species, with a wide range of equipment, brought ashore in many different places. 

“Trying to manage that from an under-resourced ministry of fisheries in the capital city is basically an impossible task,” says Tim Daw at the University of East Anglia. Faraway authorities setting the rules but lacking the funds to enforce them are a major reason why fisheries around the world are in decline, he says.

But Daw says that is changing. In the last decade or so, civil society groups and researchers have been helping fishing communities come together to set their own rules and enforcement mechanisms.

“Rather than a centralized state actor trying to manage fisheries, it’s a cooperation between the state and the local people, with much more emphasis on the local people,” he says.

Communities may decide to close off certain areas to fishing, for example, or restrict what kinds of equipment can be used. The Kenyan community McClanahan worked with decided to ban the use of very-fine-mesh nets that catch almost any kind of fish, large or small. 

“And sure enough, within months - six or seven months - the catch started to slowly rise, and it’s actually been rising since that happened,” McClanahan says.

And as the catch rose, so did incomes. 

Getting everyone to follow the rules was not easy. But now the community elders tell him they will never go back. 

However, McClanahan says, there is more to the story.

“Even though the fish catch has come back - the fish are getting bigger - the reef is not in good shape," he says. "Ecologically, it’s not a success story.”

That's the big question for supporters of community fishery management: can it improve both livelihoods and ecosystems?

In a recent study, published in the Proceedings of the National Academy of Sciences, McClanahan, Daw and their colleagues studied 42 locations in five countries on two oceans. They interviewed more than 1,000 fishers and local leaders.

They found that people were generally better off with community management than without it. And there were generally more fish in community managed systems than without. 

But not always. 

“When we actually got in the water and looked at how much fish was there, the strongest driver there was the distance to market,” Daw says.

Even with community management, when fishers could easily get their catch to a market, they had a strong incentive to overfish, according to Daw.

“The value of the fish that you can catch from there is going to be higher, there is going to be more pressure on those resources, they’re going to be attractive to more people," he says. "And we see that as there being actually less fish left on the reefs.”

Also, the more dependent fishers were on their catch for food or income, the less well the systems worked. 

And community management did not work equally for everyone. Wealthier people tended to benefit more, perhaps because they had more influence over how the rules were made or enforced than poorer people did. 

But Tim McClanahan says, “There was evidence the wealthy were doing well, but the poor were either doing a little bit better or not any worse.”

The study backs up what Indiana University political science professor Elinor Ostrom has found with groundwater, pastures or other resources that communities share but no one owns.

“Our own research has been showing that small community-controlled resource governance can - CAN - work," she says. "But all of our studies have also shown that it isn’t a panacea. It doesn’t always work.”

Ostrom should know - she won a Nobel Prize for her research. 

She says when people have a stake in making the rules and have effective ways of enforcing them, communities can do a better job than governments at managing a common resource.