But while the aquaculture industry is more efficient than ever, it is putting a strain on marine resources by consuming large amounts of feed made from wild fish harvested from the sea, the study shows.
"Aquaculture is set to reach a landmark in 2009, supplying half of the total fish and shellfish for human consumption," the authors write in their paper, published in Monday's online edition of the Proceedings of the National Academy of Sciences.
While the fish that end up on dinner plates are produced in farms, they are fed fish meal made from wild-caught fish, putting pressure on marine fisheries - a problem warned about by ocean explorer Jacques Cousteau back in 1992 at the United Nations Earth Summit in Rio de Janeiro.
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, the authors point out. Oily fish, such as salmon, are a major source of omega-3s, which reduce the risk of cardiovascular disease, according to the National Institutes of Health.
Fish farm in Norway, July 2009 (Photo by C. Ridge)
"The huge expansion is being driven by demand," said the Stanford study's lead author Rosamond Naylor, a professor of environmental Earth system science at Stanford University and director of the Stanford Program on Food Security and the Environment. "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."
To maximize growth and enhance flavor, fish farms use tons of fishmeal and fish oil made from less valuable wild-caught species, including anchoveta and sardines.
"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 write in the study.
In 2006, aquaculture production was 51.7 million metric tons of farmed fish, and about 20 million metric tons of wild fish were harvested for the production of fishmeal to feed the farmed fish.
"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 lower the amount of fish oil in the salmon's diet. The authors say a four percent reduction in fish oil would reduce the amount of wild fish needed to produce one pound of salmon from five pounds to 3.9 pounds.
But reducing fishmeal use by four 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.
Vegetarian species, such as Chinese carp and tilapia, can be raised on feed made from plants instead of wild-caught fish, say the authors, so these farmed species have been considered environmentally friendly.
Fish farm in the Philippines (Photo by Michael Mesina)
But in the early 1990s, vegetarian fish farms began adding fishmeal to their feed to increase yields.
Although between 1995 and 2007 fish farmers reduced the share of fishmeal in carp diets by 50 percent and in tilapia diets by nearly two-thirds, by 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, according to the report.
"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."
There are other environmental problems associated with aquaculture, a May 2008 report by the Government Accountability Office points out. These include the release of concentrated amounts of fish food, wastes, and chemicals or antibiotics into ocean waters. Escaped farmed fish mix with or outcompete wild fish for food and habitat; and diseases and parasites such as sea lice spread from fish farms to wild fish populations.
"Better alternatives exist for meeting the ever-rising demand for seafood and growing a cleaner, greener, safer seafood production industry to supplement, rather than overtake, wild-catch fisheries in the United States," says Food & Water Watch Fish Program Director Marianne Cufone.
Divers observe a submerged fish cage offshore Oahu owned by Cates International in which Pacific threadfin, known locally as moi, are raised. (Photo courtesy NOAA)
"Land-based, recirculating aquaculture systems, commonly called RAS, are closed-loop facilities that retain and treat the water in the system," Cufone explains. This method of fish farming can reduce discharge of waste, the need for antibiotics or chemicals used to combat disease, and fish and parasite escapes."
"RAS are not connected to open waters, and therefore can be used to grow a wide range of plants and fish without threatening the environment or competing with fishermen. Innovative technologies are being used to reduce energy usage and wild fish in feed for RAS," Cufone says.
On the policy front, Naylor praised the California's Sustainable Oceans Act and the proposed National Offshore Aquaculture Act, both of which call for reductions in the use of fishmeal and fish oil in feeds.
"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."
She applauds plans by the National Oceanic and Atmospheric Administration to develop a comprehensive national policy that addresses fisheries management issues posed by aquaculture.
On September 3, NOAA announced its intent to develop a comprehensive national policy for sustainable marine aquaculture, providing a framework for addressing aquaculture activity in federal waters. The national policy also is expected to provide context for the Fishery Management Plan for Regulating Offshore Aquaculture in the Gulf of Mexico, which took effect on September 3.
"We will develop a national policy that focuses on the protection of ocean resources and marine ecosystems, addresses the fisheries management issues posed by aquaculture, and allows U.S. aquaculture to proceed in a sustainable way," said NOAA Administrator Dr. Jane Lubchenco.
The House Natural Resources Committee, Subcommittee on Insular Affairs, Oceans and Wildlife, led by Congresswoman Madeleine Bordallo of Guam, will hold an oversight hearing on Offshore Aquaculture on Wednesday. The subcommittee will hear from federal and California state officials, representatives of the fishing and aquaculture industries and environmental groups such as the Ocean Conservancy and the National Coalition for Marine Conservation.
For a link to the live webcast on the day of the hearing, go to: http://resourcescommittee.house.gov/index.php. Look for the "webcasts" logo on the pick list to the left.
Copyright Environment News Service, ENS, 2009. All rights reserved.