With a growing population, the world is looking more and more to the ocean as a source of food. But wild stocks of fish and other seafoods are being overexploited in many areas. Now, a study from UCLA suggests that if fish farming can be moved offshore, then an area of sea the size of Lake Michigan (0.025 percent of the ocean's surface), could meet the global demand for fish and allow wild stock to recover.

Fish is big business. According to the Food and Agriculture Organization of the United Nations, global per capita fish consumption exceeded 20 kg (44 lb) for the first time in 2016. That works out to exports of 73.8 million tonnes worth US$148 billion. Seafood is a major source of protein in many parts of the globe and nutritionists claim that diets with higher percentages of fish are healthier.

The trouble is, the wild fish stocks are under severe pressure from the growing demand, with 57 percent of the stocks overfished to the point of population decline, and another 30 percent classed as overexploited or recovering.

One way of overcoming this is by fish farming or aquaculture. It's not a new idea. Aquaculture dates back to prehistoric times when the first hunter gatherers hit on the idea of keeping fish in pens rather than eating them right away. Over the centuries, fish and shellfish have been cultivated in flooded rice paddies, specially made ponds, and pens in natural ponds, lakes, and estuaries to provide a reliable source of Friday dinners.

Today, fish farming is also big business, with trout, shrimp, salmon, eels, oysters, molluscs, clams, carp, and many others produced in vast numbers. It's a modern success story, but the potential for growth is limited because fish farming in sheltered bays, estuaries, and streams limits where many farms can be established. Fish farming in shallow waters also makes them susceptible to diseases and parasites, as well as making them a source of pollution from fish droppings.

But the new UCLA study led by Peter Kareiva and Rebecca Gentry, indicates that if aquaculture could be moved into deeper offshore waters or, eventually, into the open sea, then the yields produced would easily dwarf the output of the entire present fishing industry. In addition, it would do so with not only less environmental damage, but would actually help reverse the effects of wild fishing, and would be a great economic and nutritional boon to many developing countries.

The UCLA team looked at aquaculture in very broad terms instead of focusing on specific species, as previous research had. Looking at the world's oceans, they eliminated areas where fish cultivation was impractical, such as shipping lanes, marine sanctuaries, off-shore drilling and mining areas, and areas marked by pollution and other environmental hazards. They then studied the physiology of 180 species of finned fishes and bivalves that are farmed, noting what environments they thrived in based on ocean depth, temperature, and their biological needs.

They then eliminated areas in the deep ocean far from the continental shelves. Though these areas might one day be used for aquaculture, the scientists rejected them because current technology and the need for large infrastructure to build, maintain, and service such farms would make them impractical at present.

What they found was surprising. Areas like North America and Europe, which have the capital and technology to exploit ocean-based aquaculture, didn't come out well because heavy environmental regulations make establishing such farms an arduous and expensive process. Meanwhile, other areas were deemed unsuitable because such regulations were too lax, resulting in coastal pollution.

But tropical countries showed the highest production potential, with Guinea in Africa, Bangladesh in Asia, and Uruguay in South America ranking the highest – all areas marked by food insecurity issues. According to the study, nations like Argentina, Indonesia, and India not only have burgeoning populations and poverty issues, they also have fertile seas that could not only feed their people, but provide welcome export dollars.

Along with these benefits, the UCLA team contends that ocean aquaculture would be able to feed the world while improving the lot of wild fish stocks. Because fish farming offshore will be expensive at first, conventional fishing will still be a major player, but farmed seafood would remove most of the pressure to fish vulnerable stocks and allow overfished areas to recover properly as well as making it feasible to place more areas of the ocean off limits from exploitation.

"We need to find more protein for our growing population, and we have pretty much tapped out wild fish as protein sources," says Kareiva. "This study shows that farming fish in the ocean could play a huge role in feeding people without degrading our ocean or overfishing wild species."

The study was published in Nature (PDF).