for National Geographic News
Fish are fattening up faster near the Pacific's surface, which is warming, while species in the deep sea are growing more slowly as that water cools, a new study says.
The shallow-living fish are growing 20 to 30 percent faster today than they were 50 years ago, according to the researchers' analysis of fish ear bones.
The faster growth rates closely match a warming trend in the ocean's surface waters.
"There's no question that the shallow-water fish are tracking our local version of global climate warming," said Tasmania, Australia-based Ronald Thresher, a fisheries biologist with the Commonwealth Scientific and Industrial Research Organization.
The faster growth, he added, could make the near-surface fish more resilient to overfishing. (Related: "Warming Oceans Put Kink in Food Chain, Study Says" [January 30, 2007].)
By contrast, deepwater fish are growing 20 to 30 percent slower than they were 50 years ago. Their slowing growth rates correlate with a long-term cooling of the deep waters.
The cause of the cooling trend is unclear. But analysis of deepwater corals suggests it has been going on for centuries and may be independent of global warming, Thresher said.
The slowing growth of deepwater fish raises concern about commercially valuable species such as orange roughy, Thresher and his colleagues note this week in the journal Proceedings of the National Academy of Sciences.
"It looks like there's more than one factor going on which might reduce their productivity—not just the fishing but also environmental changes," Thresher said.
For example, fish that grow slowly—and therefore stay juveniles longer—are weaker and more susceptible to predation and starvation.
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