Fish Growing Faster in Warming Waters

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The researchers examined bony structures in fish's earlike organs to determine the growth rates of more than 500 commercially caught fish. The fish ranged in age from 4 to 128 years.

"If you take one of these [bony structures] and whack them in half, you can see these little growth increments," Thresher said.

The increments are similar to tree rings. Wider spaces between rings represent faster growth.

The team saw "a pretty substantial slowdown in the growth rates for the deepwater ones and a very significant increase for the shallow water ones," Thresher said.

Temperature Affect

When the researchers compared the fish growth rates with surface and deepwater temperature records, the team found a tight fit.

Thresher said several scientific studies indicate that temperature has an effect on the growth rates of cold-blooded animals, including fish.

"The temperature thing is a highly significant correlation and makes a lot of good sense from a biological perspective," Thresher said.

Frank Schwing is an oceanographer with the National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center in Pacific Grove, California.

He commented in an email that the discovery that water temperature affects growth rates is not surprising. But, he said, it "is just one of many, often competing, impacts of climate change" on fish.

For example, warming oceans could also disrupt the food chain, shift migratory patterns, and disturb reproductive cycles. Fisheries managers need to consider all these factors, he said.

Boris Worm is a marine biologist at Dalhousie University in Halifax, Canada, who studies changes in marine biodiversity.

Impressed by the new study, he said the climate effect on long-lived and easily overfished deepwater species like orange roughy is of particular concern.

"If you have fishing pressure and at the same time this slowing down of growth rates due to climate change, you have a double-whammy effect," he said.

The finding, Worm added, should make managers of these deepwater fisheries more cautious.

"And we're not really managing them very carefully to start with."

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