Aquaculture, once a fledgling industry, now accounts for 50 percent of the fish consumed globally, determines a new report by an international team of researchers.
The 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, according to the authors."
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," Naylor added.
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," said the authors.
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.