CORVALLIS, Ore. - A new report in the journal Science suggests that some types of aquaculture, a fish-farming concept that once seemed to be the solution to overfishing of the world's oceans, may in fact be causing some of the same problems it was meant to resolve.
Shrimp and salmon aquaculture, in particular, were indicted for depleting fisheries, disrupting coastal ecosystems, polluting the ocean with excess nutrients and pesticides, and using almost triple the quantity of wild-caught fish for "fish food" as the system produces in marketable shrimp or salmon.
"Aquaculture is often seen as a panacea, the solution to relieve fishing pressure on the oceans and feed the world," said Jane Lubchenco, a distinguished professor of zoology at Oregon State University and co-author of the report.
"What we're finding is that, unless it is done right, some aquaculture is causing more problems than it solves and doing nothing to increase the world's overall food supply."
Lubchenco and nine other international experts in aquaculture, fisheries, ecology and economics suggested that improved practices are needed to make salmon and shrimp aquaculture more sustainable. For example, the amount of fish required to make feed for salmon and shrimp should be reduced, pollution from aquaculture operations should be minimized and habitat destruction prevented.
Both the industry and government should consider new regulations, pollution taxes, or reduction of financial subsidies for the most harmful types of aquaculture until some of the problems are addressed, the researchers said.
According to the report, some of the worst problems with aquaculture develop with species such as shrimp and salmon that are carnivores and require high levels of fish meal and fish oil in their diets. Instead of becoming a substitute for ocean fishing, they actually draw down the ocean resources that support all fish production, the report said.
And the issues involved are increasingly a big business. Farmed shrimp is now produced in 50 countries, most of them developing nations in the tropics, with a global value of $6 billion a year. The salmon produced largely in temperate zones are a $2 billion crop which has expanded rapidly since the late 1970s due to improved technology, high profits and government subsidy.
Global aquaculture now accounts for one-fourth of all fish consumed by humans. Almost half of the salmon and nearly one fourth of the shrimp consumed worldwide now comes from farms.
Among the problems caused by shrimp and salmon aquaculture:
- Shrimp aquaculture ponds can destroy mangroves and other nursery areas that support ocean fisheries, provide livelihoods for indigenous peoples and protect coral reefs.
- Fish farming discharges nutrients, pesticides and antibiotics into coastal waters.
- Exotic fish species are sometimes introduced outside their native habitat.
- The ocean's capacity to assimilate wastes, provide feed and stock, and maintain viable fish populations is being challenged.
- The viability of tropical ponds used to rear shrimp often collapses after 5-10 years of use from disease, chemical and biological pollution, creating a "boom and bust" economic cycle and disruption of local communities.
A big part of the problem, the report said, are the huge amounts of fish needed to produce fish meal and oil for the "delicacy" species such as shrimp and salmon that bring top prices in the market. It can take 1.8 million tons of wild fish to produce 644,000 tons of salmon.
Meanwhile, salmon netpens send volumes of feces and uneaten food directly into coastal waters. One analysis of the Nordic salmon farming industry showed that it discharged quantities of nitrogen equal to the amount in untreated sewage from a population of 3.9 million people. And there are concerns that escaped, farmed salmon may lead to genetic degradation of wild salmon populations.
"Rapid growth in shrimp and salmon farming has clearly caused environmental degradation, while contributing little to world food security," the researchers said in the report. "These industries provide food mainly for industrialized countries, consume vast quantities of wild fish as feed, and generally do not generate long-term income growth in impoverished communities."
According to Lubchenco, salmon aquaculture in the Pacific Northwest faces similar issues.
"Now that some of these problems are being recognized, they can begin to be addressed," she said. "Incentives which reward good practices should be established, which could operate at local to international levels."
In the Science report, the researchers suggested that a good mechanism to improve production practices might be trade restrictions through the World Trade Organization that addressed the processes of production, not just quality of products.