Half of fish consumed globally is now raised on farms, study finds
<http://www.sciencedaily.com/releases/2009/09/090907162320.htm>

ScienceDaily (Sep. 8, 2009)

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."

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 5 pounds of wild fish to produce 1 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 fish needed to produce 1 pound of salmon from 5 pounds 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.

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.

On the policy front, Naylor pointed to California's 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."