As governments, researchers and farmers wonder how to feed more than nine billion hungry mouths come 2050, the answer could lie in the oceans.
In 1950, it reached two and a half billion, today it's topped seven billion and come 2050, United Nations demographers predict the world population will exceed nine billion. Most of this growth will take place in developing countries, where populations will get wealthier and hungrier. And herein lies the problem.
Put simply, rich people demand more animal protein, and in a big way. While in today's poorest nations, only 15 per cent of protein comes from meat or fish, this figure rockets to 70 per cent in the wealthiest nations. The effects will be profound.
As marine ecologist Professor Steve Gaines from the University of California, Santa Barbara, puts it: "I've looked at recent projections on what the global increase in demand for animal protein will be and it's shocking; we expect around an 80 per cent increase by 2050."
Figures from the UN confirm Prof Gaines's concerns. Its Food and Agriculture Organisation (FAO) states annual meat production will need to rise by more than 200 million tonnes, to 470 million tonnes, while cereal production to feed humans and animals must increase by nearly 50 per cent to three billion tonnes, to meet 2050 demands.
The world's water and land resources will be stretched. Factor in climate change forecasts of altering rainfall patterns – more droughts and floods – and it's easy to see why researchers such as Prof Gaines are so concerned about delivering the world the protein it craves.
Last year, Prof Gaines joined forces with terrestrial ecologist Professor David Tilman from the College of Biological Sciences, University of Minnesota. In late 2011, Prof Tilman published a seminal paper showing how, largely thanks to land clearing for new crop growth, agriculture's greenhouse gas emissions could double by 2050, threatening many species with extinction. Analyses revealed ways to minimise environmental damage but as Prof Gaines says: "The basic message was that all options are terrible in terms of environment costs."
So now he, Prof Tilman and colleagues are repeating the research, but this time bringing oceans into the equation. Our seas provide protein in two key ways; either via wild fish caught from commercial fishing in world fisheries, or through farmed fish and seafood reared via aquafarming, also known as aquaculture. The researchers are still crunching data but already aquaculture looks favourite to solve the protein problem.
"We can increase the numbers of wild fish caught by fixing fisheries that have been over-fished, but even if we fixed every fishery on the planet, we can only increase production by a few tens of per cent, and that doesn't even cover 10 per cent of projected growth of animal protein demand," says Prof Gaines.
"However, our analyses show aquaculture can significantly lower the environmental impacts compared to producing the same amount of protein on land and also has the potential to meet growth in protein demand," he asserts.
Aquaculture is the farming of any saltwater or freshwater aquatic organism from aquatic plant and crustacean to mollusc and fish. And it's already big business.
According to the FAO, aquaculture continues to be the world's fastest growing animal food-producing sector and is set to overtake wild capture fisheries as a source of fish. In the 1950s, production came in at less than one million tonnes per year, today this figure has increased to more than 51 million tonnes a year.
Matt Elliot, conservation director of the Sea Change Investment Fund at US-based California Environmental Associates, is watching the industry carefully. He says: "Aquaculture is growing at a remarkable rate; last decade global production grew at 7 per cent a year, that's double the rate of terrestrial animal protein production."
Salmon farming – most notably in the Atlantic – has mushroomed across Canada and Europe in the last decade, but Asia-based players are without a doubt leading the way. "Ninety per cent of global aquaculture takes place in Asia with 60 per cent of this in China," says Elliot. "A lot of production is freshwater fish farming, including carp, and also shellfish in the marine environment."
But this is where the waters grow murky. Rapid growth has come at a cost. Production pressures have led to dense salmon farming in Canada and Northern Europe while China-based manufacturers have been packing their catfish, shrimp and tilapia ponds very, very tightly. In each case, excessive fish waste has helped to spread disease and pollution among wild fish while unwanted nutrients have overloaded coastal waters, strangling sea-life.
And then there's the thorny issue of fish feed. Many of the most popular species of farmed fish are carnivores that need to be fed, at least partly, with other fish either in the form of fishmeal or oil. The FAO states it takes around 25 million tonnes of fishmeal to produce 30 million tonnes of fish and crustaceans, with fishmeal production having rocketed from three million to 28 million tonnes in the last 50 years.
Critically for the industry, this increase in fish feed production cannot continue. Feeding fish to fish is a constraint, with the total amount of fish available for feed unlikely to increase.
"Historically the amount of fish we take out of the ocean and turn into fishmeal is a quarter of global landing and this has remained constant," explains Elliot. "Certain types of fish, such as anchovies, are turned into fishmeal, and while the fisheries for these are not perfectly managed, even with better management it would be difficult to substantially increase yields."
But despite the industry's dubious farming practices and limited fish food supplies, a transition towards aquaculture still has key advantages.
As Elliot highlights, myriad life cycle analyses of farmed fish practices concur that aquaculture produces fewer greenhouse gas emissions than any land-based farming methods. What's more, the industry has seen a steady decline in the amount of fishmeal and oil in its fishes' diets.
"Researchers have projected this 'inclusion rate' will continue to fall over time," adds Elliot.
And crucially, much research is underway to develop alternatives to ground-up fishmeal that don't draw resources from the human food chain and could prove revolutionary in terms of reducing environmental impacts. For example, Professor Margaret Overland from the Norwegian University of Life Sciences is developing feeds based on biomass for fish. Plant-based feeds contain carbohydrates, fibre and starch that carnivorous fish can't digest, but Prof Overland and her team are adding microbial organisms such as yeast that convert low value biomass, such as wood, into high-protein feed ingredients.
Developments in 'integrated multi-trophic aquaculture' – in which the by-products and waste from one aquatic species are fed to another – are also making a difference. Researchers from the University of New Brunswick are growing mussels and kelp alongside caged Atlantic salmon in the Bay of Fundy, Canada. Here, salmon waste fertilises the seaweed, which can be harvested for fish feed, and also feeds the mussels. Similarly, researchers from Bangladesh Agricultural University are growing carp alongside freshwater snails and water spinach in their production ponds.
And on the other side of the Atlantic, co-location – locating farmed species with offshore structures – is gathering pace. A recent UK trial saw Wales-based mussel producer, Deepdock, cultivating mussels at the North Hoyle Wind Farm with support from UK seafood industry authority, Seafish. Following the trial's success, the European Fisheries Fund has now stumped up support to encourage more shellfish co-location at Welsh offshore wind farms.
As Prof Gaines completes his analyses that confirm the promise of aquaculture to provide more protein, his enthusiasm for such developments is rising. His team is currently working on an offshore cage system called Aquapod to sustainably produce shrimp without providing a feedstock (see 'Brave new homes', p77).
He says: "These alternative forms of production can dramatically increase the efficiency of aquaculture. Feeding fish with fishmeal and agricultural food products is no longer viable, so these kinds of technology alternatives are going to be key."
But as many aquaculturists rush to develop innovative ways to feed and produce fish and seafood, other players believe it's time the industry started to move back down the food chain.
US-based independent aquaculture consultant John Forster started his aquaculture career in the 1970s, running a UK-based trout farm, before crossing the Atlantic to set up salmon and sturgeon farming in Washington, US. Today, the aquaculture veteran advocates a different kind of farming; seaweed.
"We catch something like 100 million tonnes of fish from the ocean every year, but the plant material that went through the food chain is something like nine billion tonnes," he says. "Many of the higher level carnivores we catch in the ocean are four or five steps up the food chain, but if we're really going to feed ourselves we need to go down the food chain and use more primary production."
As Forster highlights, these relatively 'large plants' only make up around 3 per cent of the ocean's total primary production as natural growth is confined to shorelines and coastal habitats. But farming offshore on artificial floats would boost production and the resultant biomass could be harvested and processed into food, fish feed, even biofuel.
His thoughts aren't new. Asia has been farming seaweed for decades with its annual production having increased nearly ten-fold in the last 40 years. And now, small outlets such as US-based Ocean Approved, which sells kelp products for human consumption, are emerging.
But still seaweed production hasn't found favour with most. Last year, US bio-engineers at California-based Bio Architecture Lab developed a microbe to digest carbohydrates in brown seaweed and produce biofuel. Researchers applauded the breakthrough but questioned whether enough seaweed could ever be harvested to make such a development worthwhile.
Despite its potential, seaweed production remains a tiny fraction of land-based plant agriculture, and this, Forster believes, should change.
"As seaweed starts to evolve the industry could look at processing techniques to allow nutrient extraction for animals," he says.
For example, soya beans are roasted and processed to produce soybean meal, a protein source widely used in fish feed, so why not seaweed?
Forster also believes research and development could help an industry breed and grow more valuable strains of seaweed. "Genetics, irrigation and fertilisers all allowed land-based agriculture to become massively more efficient," he says. "Look at an early genome of corn, it's pathetic and resembles a blade of grass compared to the full heads of corn we have today. There's potential if we put our minds to doing it."
And perhaps this is the crux of the matter for aquaculture. While the industry is in its infancy, it has the potential to supplement land-based farming and increase the planet's capacity to support the growing human population. Expansion would demand significant development and investment, but when we've farmed the land, what choice is there but to farm the sea as well?
As Forster says, the sea makes up 70 per cent of the planet's surface. "Now we have to work out how can we get this 70 per cent to be more productive." he explains. "It doesn't make sense to me that we still only get just over 1 per cent of our food from the oceans, somewhere in there has to be opportunity."