Aquaculture imposing heavy burden on marine resources

The report attributes the burden to consumption of large amounts of feed derived from wild sea fish. “Aquaculture is set to reach a landmark in 2009, supplying half of the total fish and shellfish for human consumption,” said lead author Rosamond L. Naylor, a professor of environmental earth system science at Stanford University.

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 Institute of Health.

“The huge expansion is being driven by demand,” said Naylor. “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 maximise growth and enhance flavour, aquaculture farms use large quantities of fishmeal and fish oil made from less valuable wild-caught species, including anchovy and sardine.  “With the production of farmed fish eclipsing that of nature raised 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 author wrote.

In 2006, aquaculture production was 51.7 million metric tonnes, and about 20 million metric tonnes of wild fish were harvested for the production of fishmeal. “It can take up to five pounds (2.5 kg) of wild fish to produce one pound (half kg) of salmon, and we eat a lot of salmon,” said Naylor.

One way to make salmon farming more environmentally sustainable is to simply lower the amount of fish oil in the salmon’s diet, says a Stanford release.  Their findings were published in the Monday online edition of the Proceedings of the National Academy of Sciences (PNAS).