Friday, November 03, 2006

Sayonara, sushi... - Nature

Published online: 2 November 2006
; | doi:10.1038/news061030-10

Time could be running out for seafood.

Heidi Ledford

Salmon, like all seafood: predicted to collapse by 2048.

What's your favourite seafood dish? Seared scallops? Salmon sashimi? Grilled shrimp?

Enjoy it while you can, because by 2048 it could all be gone. A recent survey of global fisheries data says that seafood stocks around the world will collapse within 50 years — if we don't change the way we treat the world's oceans1.

"That's the end of the line," says Boris Worm, a marine conservation biologist at Dalhousie University in Halifax, Nova Scotia, and lead author on the study. "Whatever your favourite seafood is, you will most likely not be able to eat it anymore."

Worm and his colleagues reached this conclusion by analysing more than 50 years worth of data from the Sea Around Us Project — a database containing almost 500 million records of catch rates from fisheries around the world and based at the University of British Columbia in Vancouver. The international team of researchers used this data to model the ocean's bounty over time.

Their calculations showed a precipitous drop in coastal biodiversity over the past 200 years, along with a concomitant decline in water quality and a surge in harmful algal blooms, coastal flooding and fish kills. Analysis of data from large marine ecosystems indicated that 29% of the seafood stocks available in 1950 had already collapsed as of 2003, and the remainder would follow by 2048.

Fortunately Worm's analyses also showed that current conservation efforts have succeeded in reversing fishery decline in some regions. Worm hopes that conservation plans and fishing management will prevent us from ever reaching the point of total collapse. "I'm optimistically convinced that we will not hit 100% at 2048 because we will turn things around before that," he says.

Saving seafood

To prevent the collapse of the seafood industry, Worm says, fishing should focus on stocks such as herring and mackerel, which are less sensitive to heavy fishing. Habitat restoration, pollution reduction and a slowdown in climate change will also be key factors in reversing current trends, he adds.

Efforts like these can restore biodiversity to marine ecosystems, which will make them more productive and so more resistant to disturbing factors such as storms and fishing.

Whatever your favourite seafood is, you will most likely not be able to eat it anymore.

Boris Worm,
Dalhousie University in Halifax, Nova Scotia
In addition, a recent report from George Sugihara of the Scripps Institution of Oceanography in La Jolla, California, suggests that preserving the larger, older fish within a population would make it more resistant to collapse2.

Point of collapse

Steve Murawski, chief scientist at the US National Oceanographic and Atmospheric Administration's Fisheries Service, agrees that seafood supply needs to be actively protected. But, he says, Worm's models rely on a definition of 'collapse' - the point at which a fishery's yield dips below 10% of its historic maximum - that may not truly reflect fishery conditions.

"That's not a good metric of what a healthy stock would be," says Murawski. "In many cases that high catch occurred because you were dramatically overfishing the stock." Evaluating stocks relative to an overfishing event sets the bar artificially high, Murawski argues, leading researchers to conclude that a fishery has collapsed even if it is being stably maintained.

Worm concedes Murawski's point, but points out that catch data is the only global data available. Meanwhile, he adds, the trend in his data is clear even if a precise date for worldwide seafood collapse may vary.

"It's like a lemon," says Worm. "We have to press harder and harder to get juice out of it. At some point we just can't force more out — we're going to start running out of species."

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