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.
