Eating fish: Good for heart, but bad for environment?

HALIFAX, Nova Scotia, Aug 10 (Reuters) - Doctors recommend a good dose of salmon or tuna in the diet because of its benefits to the heart. But is it good for the environment? Surging demand for salmon in particular has been spurred in part by numerous studies touting the health benefits of omega-3 fatty acids, which are present in some kinds of fish.

A study published in June in the American Heart Association journal Circulation said a diet with liberal servings of fish, nuts and seeds rich in such nutrients can help lower a person's blood pressure. Other studies have shown benefits to eye and brain development and preventing heart disease, Alzheimer's disease and eye disorders.

Conservationists point out that while global fish stocks were getting hammered long before sushi became chic, health trends could add pressure to already vulnerable fisheries.

"Over-fishing has predated the interest in omega-3 and healthy eating. But now there are places where it is certainly going to accentuate it," said Jason Clay, vice president of markets at the World Wildlife Fund (WWF).

"The FAO (U.N. Food and Agriculture Organization) estimates that by 2030 average annual per capita global consumption of fish will increase by 1.5 kgs (3.4 pounds) and some of it will be driven by health-related demand," he said.

When it comes to omega-3 fatty acids, not all fish are equal. Fatty fish such as trout, salmon, mackerel and Alaska pollock are rich in this crucial group of nutrients. Tuna are, too, but few wild tuna fisheries are regarded by conservationists as sustainable. "It depends on your source ... Omega-3s are very high in wild salmon and the Alaskan salmon fishery is well-managed," said Phil Kline, an ocean campaigner with Greenpeace.

Alaska salmon are among the fisheries that have been certified as sustainable by the British-based Marine Stewardship Council. It uses stringent criteria for a fishery to get its seal of approval and the right to bear its eco-label. It has not yet given its blessing to any tuna fishery but is assessing the sustainability of the U.S. Pacific coast albacore tuna industry.

Demand for salmon has certainly been soaring. According to the U.S. National Fisheries Institute, American per capita consumption of salmon has risen from 0.87 pounds (0.39 kg) per year in 1992 to 2.026 pounds (0.92 kg) in 2006. The species also went from being America's sixth most popular fish to eat to its third over the same period of time.

In a well-managed situation, such demand can lead to conservation: it's in no one's interest to deplete something of value."In the long run, the more valuable wild salmon are the better they are likely to be protected," said Gunnar Knapp, a professor of economics at the University of Alaska's Institute of Social and Economic Research.

He said high demand and prices gave people an incentive to protect vital salmon habitat such as spawning grounds in rivers from other industries such as logging and mining."In Alaska, even if the price of salmon were to quadruple it would not lead to too many fish being caught because the limiting factor is not the price but how much the managers allow the fishermen to catch, and they make that assessment purely on biological grounds," Knapp told Reuters by phone from Anchorage. But he said Russia's salmon fishery, for example, was not so well managed and could suffer overfishing as prices rise.

Much of the burgeoning demand for salmon is being met by the rapidly growing aquaculture industry, but experts say there are environmental concerns linked to that, too. WWF's Clay said fish being caught for fishmeal to feed the aquaculture industry include species such as anchovies, which are rich in omega-3s but which have questions over their sustainability."One out of every three fish that is caught right now is used to make feed for other fish," he said. Fish don't actually produce omega-3 fatty acids, they capture it from the food chain.

And there are plenty of substitutes out there such as walnuts, flaxseed and canola oil, which can provide the same omega-3-related benefits as fish. In the past, children in many parts of the world were given cod liver oil as a health supplement. These days, they are more likely to take fish oil capsules made from other species.