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Shrinking at Sea: Harvesting drives evolution toward smaller fishes

Fish are becoming smaller and growing more slowly in response to pressures introduced by fishing, scientists say. That shift, which new data suggest is hard to undo, creates populations of fish that are poor at reproducing and inefficient at bulking up.

Commercial fishing is generating a "Darwinian debt," in the form of less valuable fishes, that could take generations to pay off, says Ulf Dieckmann of the International Institute for Applied Systems Analysis in Laxenburg, Austria.

People have long noted a downward trend in the average size of fish of many species. That's not surprising. Small fish are more likely than large ones to slither from nets. Also, laws intended to protect juveniles often require that fish smaller than a certain size be returned to the sea.

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