Oyster extinctions worldwide

Oyster bed, SC: courtesy Doug DuCap Food and Travel

Oysters grow best where fresh and salt water mix. Over centuries their shells form reefs, make key fish habitat, and protect shorelines against erosion. Their disappearance is an unmistakable sign of ecosystem stress.

85-90 percent of the world's oyster reefs have now been lost, in 144 bays and 44 ecoregions around the globe, according to an in-depth study by international scientists. (1)

People have forgotten how abundant oysters were," says lead author Dr Michael Beck. "In San Francisco in the 19th century, they fed workers building the transcontinental railroad. There were so many of them that the writer Jack London was both an oyster pirate and an oyster policeman. But today, there's not a single wild oyster bed in San Francisco Bay."

Chesapeake oysters once filtered the entire bay in a day, and gave work to 9000 skipjack fishermen. Over the last century, 99% of its wild oysters have disappeared. (2)

Now a murky green, the English Channel was kept crystal clear -- in Julius Caesar's time -- by masses of oysters. Up to a century ago they were a staple food of the British working class, giving jobs to 120,000 catchers. Oysters are now "functionally extinct" with fewer than 1 percent of former reefs surviving in the NW Europe coast (the Wadden Sea). Scientists blame over-harvesting, pollution, disease and non-native species.

Last summer, many important reefs in the Gulf of Mexico were destroyed by so-called "clean-up" workers' release of vast amounts of Mississippi freshwater to disperse BP oil spills. Changing salt concentrations killed off as much as half the living oysters. The Gulf was the last healthy survivor of the five great North American beds.

The Beck study urges worldwide efforts to save the oyster, wherever populations have fallen to 10% of their former abundance. Marine protected areas (MPA) have helped other species recover. But local fishing interests, under pressure from their financiers, block national and international action.

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(1) Michael W. Beck of The Nature Conservancy and the University of California, Santa Cruz, et al., "Oyster Reefs at Risk and Recommendations for Conservation, Restoration, and Management" BioScience Feb 2011.

(2) Newell 1988, cited in NOAA Estimating Net Present Value in the Northern Chesapeake Bay Oyster Fishery 2008.