Aquaculture, once a fledgling industry, now accounts for 50 percent of the fish consumed globally, according to a new report by an international team of researchers. And while the industry is more efficient than ever, it is also putting a significant strain on marine resources by consuming large amounts of feed made from wild fish harvested from the sea, the authors conclude. Their findings are published in the Sept. 7 online edition of the Proceedings of the National Academy of Sciences (PNAS).

"Aquaculture is set to reach a landmark in 2009, supplying half of the total fish and shellfish for human consumption," the authors wrote. Between 1995 and 2007, global production of farmed fish nearly tripled in volume, in part because of rising consumer demand for long-chain omega-3 fatty acids. Oily fish, such as salmon, are a major source of these omega-3s, which are effective in reducing the risk of cardiovascular disease, according to the National Institutes of Health.

"The huge expansion is being driven by demand," said lead author Rosamond L. Naylor, a professor of environmental Earth system science at Stanford University and director of the Stanford Program on Food Security and the Environment. "As long as we are a health-conscious population trying to get our most healthy oils from fish, we are going to be demanding more of aquaculture and putting a lot of pressure on marine fisheries to meet that need."

Fishmeal and fish oil

To maximize growth and enhance flavor, aquaculture farms use large quantities of fishmeal and fish oil made from less valuable wild-caught species, including anchoveta and sardine. "With the production of farmed fish eclipsing that of wild fish, another major transition is also underway: Aquaculture's share of global fishmeal and fish oil consumption more than doubled over the past decade to 68 percent and 88 percent, respectively," the authors wrote.

In 2006, aquaculture production was 51.7 million metric tons, and about 20 million metric tons of wild fish were harvested for the production of fishmeal. "It can take up to five pounds of wild fish to produce one pound of salmon, and we eat a lot of salmon," said Naylor, the William Wrigley Senior Fellow at Stanford's Woods Institute for the Environment and Freeman Spogli Institute for International Studies.

One way to make salmon farming more environmentally sustainable is to simply lower the amount of fish oil in the salmon's diet. According to the authors, a mere 4 percent reduction in fish oil would significantly reduce the amount of wild-caught fish needed to produce a pound of salmon – from 5 pounds of wild fish to just 3.9 pounds. In contrast, reducing fishmeal use by 4 percent would have very little environmental impact, they said.

"Reducing the amount of fish oil in the salmon's diet definitely gets you a lot more bang for the buck than reducing the amount of fishmeal," Naylor said. "Our thirst for long-chain omega-3 oils will continue to put a lot of strain on marine ecosystems, unless we develop commercially viable alternatives soon."

Naylor and her co-authors pointed to several fish-feed substitutes currently being investigated, including protein made from grain and livestock byproducts, and long-chain omega-3 oils extracted from single-cell microorganisms and genetically modified land plants. "With appropriate economic and regulatory incentives, the transition toward alternative feedstuffs could accelerate, paving the way for a consensus that aquaculture is aiding the ocean, not depleting it," the authors wrote.

Vegetarian fish

Fishmeal and fish oil are important staples at farms that produce carnivorous fish, including salmon, trout and tuna. But vegetarian species, such as Chinese carp and tilapia, can be raised on feed made from plants instead of wild-caught fish. That's one reason why farm-raised vegetarian fish have long been considered environmentally friendly.

In the early 1990s, vegetarian fish farms began adding small amounts of fishmeal in their feed to increase yields. However, between 1995 and 2007, farmers actually reduced the share of fishmeal in carp diets by 50 percent and in tilapia diets by nearly two-thirds, according to the PNAS report. Nevertheless, in 2007, tilapia and carp farms together consumed more than 12 million metric tons of fishmeal – more than 1.5 times the amount used by shrimp and salmon farms combined.

"Our assumption about farmed tilapia and carp being environmentally friendly turns out to be wrong in aggregate, because the sheer volume is driving up the demand," Naylor said. "Even the small amounts of fishmeal used to raise vegetarian fish add up to a lot on a global scale." Removing fishmeal from the diet of tilapia and carp would have a very positive impact on the marine environment, she added.

Regulating fisheries

On the policy front, Naylor pointed to the 2006 California Sustainable Oceans Act and the proposed National Offshore Aquaculture Act, which call for reductions in the use of fishmeal and fish oil in feeds. She also applauded plans by the National Oceanographic and Atmospheric Administration to develop a comprehensive national policy that addresses fisheries management issues posed by aquaculture. "No matter how much is done from the demand side, it is essential that there be regulation on the supply side as well," Naylor said. "You won't prevent the collapse of anchoveta, sardine and other wild fisheries unless those fisheries are carefully regulated."

Other co-authors of the PNAS study are Ronald W. Hardy, University of Idaho; Dominique P. Bureau and Katheline Hua, University of Guelph (Canada); Alice Chiu, Stanford; Matthew Elliott, Sea Change Management; Anthony P. Farrell and Ian Forster, Centre for Aquaculture and Environmental Research (Canada); Delbert M. Gatlin, Texas A&M University and the Norwegian Centres of Excellence; Rebecca J. Goldburg, Pew Charitable Trusts; and Peter D. Nichols, Commonwealth Scientific and Industrial Research Organisation (Australia).

The PNAS report was supported by the David and Lucile Packard Foundation.

Synthetic fertilizers have dramatically increased food production worldwide. But the unintended costs to the environment and human health have been substantial. Nitrogen runoff from farms has contaminated surface and groundwater and helped create massive "dead zones" in coastal areas, such as the Gulf of Mexico. And ammonia from fertilized cropland has become a major source of air pollution, while emissions of nitrous oxide form a potent greenhouse gas.

These and other negative environmental impacts have led some researchers and policymakers to call for reductions in the use of synthetic fertilizers. But in a report published in the June 19 issue of the journal Science, an international team of ecologists and agricultural experts warns against a "one-size-fits-all" approach to managing global food production.

"Most agricultural systems follow a trajectory from too little in the way of added nutrients to too much, and both extremes have substantial human and environmental costs," said lead author Peter Vitousek, a professor of biology at Stanford University and senior fellow at Stanford's Woods Institute for the Environment.

"Some parts of the world, including much of China, use far too much fertilizer," Vitousek said. "But in sub-Saharan Africa, where 250 million people remain chronically malnourished, nitrogen, phosphorus and other nutrient inputs are inadequate to maintain soil fertility."

Other co-authors of the Science report include Woods Institute Senior Fellows Pamela Matson, dean of Stanford's School of Earth Sciences, and Rosamond L. Naylor, director of the Program on Food Security and the Environment.

China and Kenya

In the report, Vitousek and colleagues compared fertilizer use in three corn-growing regions of the world--north China, western Kenya and the upper Midwestern United States.

In China, where fertilizer manufacturing is government subsidized, the average grain yield per acre grew 98 percent between 1977 and 2005, while nitrogen fertilizer use increased a dramatic 271 percent, according to government statistics. "Nutrient additions to many fields [in China] far exceed those in the United States and northern Europe--and much of the excess fertilizer is lost to the environment, degrading both air and water quality," the authors wrote.

Co-author F.S. Zhang of China Agriculture University and colleagues recently conducted a study in two intensive agricultural regions of north China in which fertilizer use is excessive. Their results showed that farmers in north China use about 525 pounds of nitrogen fertilizer per acre (588 kilograms per hectare) annually--releasing about 200 pounds of excess nitrogen per acre (227 kilograms per hectare) into the environment. Zhang and his co-workers also demonstrated that nitrogen fertilizer use could be cut in half without loss of yield or grain quality, in the process reducing nitrogen losses by more than 50 percent.

At the other extreme are the poorer countries of sub-Saharan Africa, such as Kenya and Malawi. In a 2004 study in west Kenya, co-author Pedro Sanchez and colleagues found that farmers used only about 6 pounds of nitrogen fertilizer per acre (7 kilograms per hectare)--little more than 1 percent of the total used by Chinese farmers. And unlike China, cultivated soil in Kenya suffered an annual net loss of 46 pounds of nitrogen per acre (52 kilograms per hectare) removed from the field by harvests.

"Africa is a totally different situation than China," said Sanchez, director of tropical agriculture at the Earth Institute at Columbia University. "Unlike most regions of the world, crop yields have not increased substantially in sub-Saharan Africa. Nitrogen inputs are inadequate to maintain soil fertility and to feed people. So it's not a matter of nutrient pollution but nutrient depletion."

U.S. and Europe

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A comparison of 3 agricultural areas of the world found massive imbalances in fertilizer use, resulting in malnourishment in some regions and pollution in others. Photo: David Nance, USDA

The contrast between Kenya and China is dramatic and will require vastly different solutions, the authors said. However, large-scale change is possible, they said, noting that since the 1980s, increasingly stringent national and European Union regulations and policies have reduced nitrogen surpluses substantially in northern Europe.

In the Midwestern United States, over-fertilization was the norm from the 1970s until the mid-1990s. During that period, tons of excess nitrogen and phosphorus entered the Mississippi River Basin and drained into the Gulf of Mexico, where the large influx of nutrients has triggered huge algal blooms. The decaying algae use up vast quantities of dissolved oxygen, producing a seasonal low-oxygen dead zone in the Gulf that in some years is bigger than the state of Connecticut.

Since 1995, the imbalance of nutrients--particularly phosphorus--has decreased in the Midwestern United States, in part because better farming techniques have increased yields. Statistics show that from 2003 to 2005, annual corn yields in parts of the Midwestern United States and north China were almost the same, even though Chinese farmers used six times more nitrogen fertilizer than their American counterparts and generated nearly 23 times the amount of excess nitrogen.

"U.S. farmers are managing fertilizer more efficiently now," said co-author Rosamond Naylor, who is also a professor of environmental Earth system science and senior fellow at Stanford's Freeman Spogli Institute for International Studies. "The dead zone in the Gulf of Mexico persists due to continued fertilizer runoff and animal waste from increased livestock production."

Low nitrogen in Africa

In sub-Saharan Africa, the initial challenge is to increase productivity and improve soil fertility, the authors said. To meet that challenge, co-author Sanchez recommends that impoverished farmers be given subsidies to purchase fertilizer and good-quality seeds. "In 2005, Malawi was facing a serious food shortage," he recalled. "Then the government began subsidizing fertilizer and corn seeds. In just four years production tripled, and Malawi actually became an exporter of corn."

Food production is paramount, added co-author G. Philip Robertson, a professor of crop and soil sciences at Michigan State University. "Avoiding the misery of hunger is and should be a global human priority," Robertson said. "But we should also find ways to do this without sacrificing other key aspects of human welfare, among them a clean environment. It doesn't have to be an either/or choice."

For countries where over-fertilization is a problem, the authors cited a number of techniques to reduce environmental damage. "Some of these--such as better-targeted timing and placement of nutrient inputs, modifications to livestock diets and the preservation or restoration of riparian vegetation strips--can be implemented now," they wrote.

Designing sustainable solutions also will require a lot more scientific data, they added. "Our lack of effective policies can be attributed, in part, to a lack of good on-farm data about what's happening with nutrient input and loss over time," said co-author Alan Townsend, an associate professor of ecology and evolutionary biology at the University of Colorado-Boulder. "Both China and the European Union have supported agricultural research that yields policy-relevant information on nutrient balances. But the U.S. is particularly lacking in long-term data for a country with such a well-developed scientific enterprise."

Even in Europe, with its strong research programs on nutrient balances and stringent policies for reducing fertilizer runoff, nitrogen pollution remains substantial. "The problem of mitigation of excess nitrogen loss to waters is not easily resolved," said co-author Penny Johnes, director of the Aquatic Environments Research Centre at the University of Reading, U.K. "Society may have to face some difficult decisions about modifying food production practices if real and ecologically significant reductions in nitrogen loss to waters are to be achieved."

According to Vitousek, it is important in the long run to avoid following the same path to excess in sub-Saharan Africa that occurred in the United States, Europe and China. "The past can't be altered, but the future can be and should be," he said. "Agricultural systems are not fated to move from deficit to excess. More effort will be required to develop intensive systems that maintain their yields, while minimizing their environmental footprints."

Other co-authors of the Science report are Tim Crews, Prescott College; Mark David, University of Illinois at Urbana-Champaign; Laurie Drinkwater, Cornell University; Elisabeth Holland, National Center for Atmospheric Research; John Katzenberger, Aspen Global Change Institute; Luiz Martinelli, University of São Paulo, Brazil; Generose Nziguheba, Columbia University; Dennis Ojima, The H. John Heinz III Center for Science, Economics and the Environment; and Cheryl Palm, Columbia University.

This work is based on discussions at the Aspen Global Change Institute supported by NASA, the William and Flora Hewlett Foundation, and the David and Lucile Packard Foundation; and at a meeting of the International Nitrogen Initiative sponsored by the Scientific Committee on Problems of the Environment.

Professor Walter P. Falcon, Deputy Director of the Center on Food Security and the Environment (FSE), former director of FSI, and Helen Farnsworth Professor of International Agricultural Policy, Emeritus has been recognized with an honorary degree from McGill University for his research aimed at reducing world hunger and enhancing global food security.

Professor Falcon's expertise is in food policy, commodity markets, trade policies, and regional development. Professor Falcon's current research focuses on agricultural decision-making in Indonesia and Mexico, biotechnology, climate change, and biofuels.

From 1972 to 1991, Professor Falcon served as professor of economics and director of Stanford University's Food Research Institute, after which he directed the Freeman Spogli Institute for International Studies until 1998. From 1998 to 2007 he co-directed the Center for Environmental Science and Policy. At Stanford he has also served as senior associate dean for the social sciences, a member of the academic senate, and twice a member of the University's Advisory Board.

Professor Falcon has also consulted with numerous international organizations, been a trustee of Winrock International, and was chairman of the board of the International Rice Research Institute (IRRI). From 1978 to 1980, he was a member of the Presidential Commission on World Hunger and in 1990 was named a Fellow of the American Agricultural Economics Association. From 1996-2001 he served as chairman of the board of the International Corn and Wheat Institute (CIMMYT), and from 2001-07 served on the board of the Center for International Forestry Research (CIFOR).

Falcon was cited as the outstanding 1958 graduate of Iowa State University in 1989 and in 1992 was awarded the prestigious Bintang Jasa Utama medal of merit by the government of Indonesia for twenty-five years of assistance to that country's development effort.

[See video interview with Chris Field and David Lobell here].

Biofuels such as ethanol offer an alternative to petroleum for powering our cars, but growing energy crops to produce them can compete with food crops for farmland, and clearing forests to expand farmland will aggravate the climate change problem. How can we maximize our "miles per acre" from biomass?

Researchers writing in the May 7, 2009, edition of the journal Science say the best bet is to convert the biomass to electricity rather than ethanol. They calculate that, compared to ethanol used for internal combustion engines, bioelectricity used for battery-powered vehicles would deliver an average of 80 percent more miles of transportation per acre of crops, while also providing double the greenhouse gas offsets to mitigate climate change.
 
"It's a relatively obvious question once you ask it, but nobody had really asked it before," said study co-author Christopher B. Field, director of the Department of Global Ecology at the Carnegie Institution. "The kinds of motivations that have driven people to think about developing ethanol as a vehicle fuel have been somewhat different from those that have been motivating people to think about battery electric vehicles, but the overlap is in the area of maximizing efficiency and minimizing adverse impacts on climate."
 
Field, who is also a professor of biology at Stanford University and a senior fellow at Stanford's Woods Institute for the Environment, is part of a research team that includes lead author Elliott Campbell of the University of California-Merced and David Lobell of Stanford's Program on Food Security and the Environment.