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Shrimp and salmon aquaculture depletes worldwide fishing resources, new study finds

The next time you consider tucking into a tasty piece of salmon, consider this it takes almost three pounds of wild fish to grow one pound of the commercially farmed delicacy.

Similarly, shrimp farming uses up more fish protein than it produces, and both degrade coastal regions.

These findings, based on a new interdisciplinary study, are published today in Science in an article called "Nature's Subsidies to Shrimp and Salmon Farming."

The report, the first to include a comprehensive, global analysis of the impact of shrimp and salmon farming on the environment, is based on research by 10 international specialists from a range of professional organizations. Stanford contributors include environmental biology Professor Harold Mooney and economist Rosamond Naylor, a fellow and senior researcher at the Institute for International Studies.

"What is important is that the authors are very credible scientists from both sides of the equation," said Naylor, lead author of the study. "Most of the lay community has no idea that aquaculture [of shrimp and salmon] is detrimental to the oceans' resources."

Mooney, the Paul S. Achilles Professor of Environmental Biology, said the report will give the public, for a first time, a clear picture of the real costs of eating shrimp and salmon. "This is a little truth in advertising," he said. "It's pretty sobering once you do know it. The developed countries are benefiting and, particularly for shrimp, the developing countries are paying for it."

The study goes against the commonly held assumption that fish farms add to the world's food supply and alleviate pressure on ocean resources. While the aquaculture of herbivorous species such as carp and tilapia generally provide a net gain, the opposite is true for shrimp and salmon, species that are fed diets containing large amounts of oil and meal extracted from wild-caught fish. Shrimp and salmon make up only 5 percent of farmed fish by weight, but the popular delicacies account for almost 20 percent fish farmed by value.

The report is significant because commercial aquaculture, in recent years, has been pushed by governments and international lending agencies in developing countries for its potentially quick economic returns. A quarter of all shrimp worldwide are produced in fish farms a 10-fold increase since the mid-1970s. Shrimp, primarily the tiger prawn and Pacific white shrimp, are grown mainly in developing countries for consumption in North America, Japan and Europe.

"Shrimp is a major foreign-currency earner," said Naylor, who has done research in Thailand, Indonesia and Vietnam. "It's still the most valuable [crop] in the short term. For many people, that's all that counts."

Salmon farming, which started in the 1960s in Norway, also has increased steadily since the late 1970s and is becoming the main production method for that fish. Atlantic salmon, the dominant species, is mainly grown and consumed in industrialized counties. Top producers include Norway, England, Canada, the Unites States and Chile.

Research shows that rapid growth in shrimp and salmon farming "has clearly caused environmental degradation while contributing little to world food security," the article said. Some of the unforeseen ecological consequences include:

  • The conversion of coastal ecosystems to aquaculture ponds has destroyed nursery areas that support ocean fisheries.
  • Fish farming has degraded coastal waters through discharge of nutrients and chemicals, and it has disrupted coastal ecosystems by the introduction of exotic species.
  • The ocean's capacity to assimilate wastes and maintain viable fish populations has been challenged by aquaculture's continued growth.

Despite these impacts, the report said, "producers and consumers remain unaware of and do not pay for many of the environmental and social costs of shrimp and salmon aquaculture."

The article concluded that regulation, pollution taxes and reduction of financial subsidies are "urgently needed to improve the efficiency and reduce the environmental impacts of shrimp and salmon farming." As long as the full environmental costs are not recognized in the marketplace, ocean resources including fisheries will deteriorate further, the scientists said.


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