Herring swim up the Wynants Kill two weeks after an old industrial dam was removed to allow ocean-going fish access to the Hudson River tributary for spawning and habitat in Troy, N.Y. Erica Capuana/AP hide caption

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Peruvian anchoveta being processed at a fish meal factory in Lima in 2009. The small forage species has been heavily fished. Ernesto Benavides/AFP/Getty Images hide caption

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Herring are delicious, with flaky, mild meat and oil that sizzles on their skin when grilled over a flame. Chefs and ocean advocates have been promoting the environmental and health benefits of eating small fish like this. But the case of the San Francisco Bay's herring shows some of the obstacles to spreading that message. Alastair Bland for NPR hide caption

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Lack of oxygen probably caused this mass herring die-off on Feb. 3 in an Icelandic fjord. Brynjar Gauti/AP hide caption

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