We are consuming fish faster than they can reproduce, denuding the ocean. Conventional solutions, such as forcing reductions in fishing capacity, lowering industry subsidies and imposing sustainable quotas on catches, have proved difficult to implement globally.

Creating fish banks - marine reserves where no fishing can ever take place - covering at least 20 per cent of the ocean is a bold way to tackle the problem.

When areas of the ocean are left to recover from over-fishing, the results are impressive. The number of marine species in fish banks increases by 21 per cent, on average, and the fish grow to be 28 per cent bigger, according to data on 124 reserves in 29 countries. The amount of fish per hectare increases 166 per cent, on average, and fish biomass, or total weight, shoots up 446 per cent over the next 10 years. In most cases, the fish biomass keeps rising for more than 25 years.

There are spillover effects, too. Because of the higher biomass and higher reproduction rates inside a fish bank, adjacent areas often get rejuvenated. The creation of the Columbretes Islands Marine Reserve in Spain, for instance, increased catches in surrounding fisheries by about 10 per cent a year.

In the same way, after five small fish banks were established in St Lucia, catches in adjacent areas grew by 46 to 90 per cent, depending on the gear used, over a five-year period.

These spillover effects more than offset the financial losses to fishermen caused by the creation of no-fishing zones. In Kenya and the Solomon Islands, the incomes of people living near marine reserves doubled within a decade. Reserves attract more tourists, too.

The 345,400-sq-km Great Barrier Reef Marine Park - of which 33 per cent is a marine reserve - generates around A$5.5 billion (S$7.3 billion) a year in net economic benefits and has created more than 50,000 full-time jobs.

Fish banks also help preserve ocean ecosystem benefits such as carbon sequestration. In fact, "blue carbon" projects could generate additional revenues for local communities through global carbon markets. Fish banks are not the only answer, of course, but they must be a key component of the portfolio of solutions needed to tackle the current crisis.

Finally, fish banks are an inexpensive solution. The cost of creating and managing marine reserves that would close off 20 per cent of the ocean is estimated to be as low as US$5 billion (S$6.5 billion) a year - just a small fraction of the subsidies that governments offer the fishing industry, which were upward of US$25 billion in 2003.

Moreover, the additional revenues the fish banks generate should cover the cost of managing them, making fish banks self-sustaining business opportunities - not resource sinks, as people typically perceive conservation projects to be.

Marine reserves could be easy to create if instead of relying on governments and global negotiations, we empowered local communities to develop and manage them. Policymakers would need only to facilitate the process; they should be happy to do so.

Public-private partnerships would be an effective way of getting this idea to scale quickly. Companies might be willing to invest in fish banks, covering short-term losses with long-term profits from larger catches, more tourism and "blue carbon" projects.

Creating fish banks would thus turn fishing populations from hunters into shepherds of the sea, who help protect Earth's biggest asset, the ocean. © 2012 Harvard Business School Publishing Corp (Distributed by The New York Times Syndicate)



Enric Sala is an explorer-in-residence at the National Geographic Society, based in Washington. He is a co-editor of Shifting Baselines: The Past and the Future of Ocean Fisheries.