Scientists Don’t Know Why the Planet’s Fish Are Shrinking

There are big implications to fish sizes

Fish get smaller when water temperatures rise.
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Scientists around the world have, in recent years, begun to notice something: fish are getting smaller. “The core finding is that the body size is not just predominantly shrinking but that organisms are becoming smaller through a combination of species replacement and changes within species populations,” York University’s Inês Martins told The Guardian last year.

Martins was the lead author of an international study exploring changes in the size of different species. “These trends were most evident among fish, where we saw clear evidence of shrinking body size,” Martins said. And while this shrinkage seems connected to an increase in water temperatures globally — climate change strikes again — scientists are less certain about the underlying principles behind it.

Writing in The Washington Post, Dino Grandoni explored this uncertainty — including new research that apparently debunks an earlier theory that the temperature of water where fish are raised affects their gills, which in turn affects their size.

“If it’s a global theory that the gills are going to limit growth, it shouldn’t matter if it’s a brook trout or a sardine or any other species,” the University of Massachusetts at Amherst’s Joshua Lonthair told the Post. He is one of the authors of a recent study suggesting that whatever is causing the fish to shrink, it’s not their gill capacity.

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There are a few reasons why humans should be concerned about the size of fish. One has to do with the growth of seafood as a part of human diets. Studies have suggested that people will be eating more fish in the coming decades — but if those fish are smaller, that could throw a wrench in the works.

There’s also the matter of an environment’s food chain. A species that’s growing smaller could find itself becoming a target for predators who might have stayed away from it before. Or, to put it succinctly: the impact of fish getting smaller is only getting bigger by the year.

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