Warming waters endanger up to 60% of fish species: study

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A fisherman pulls aboard a halibut near an iceberg that broke off from the Jakobshavn Glacier on July 22, 2013, in Ilulissat, Greenland. - Joe Raedle/Getty Images Europe/TNS

A new study examining fishes’ reactions to heat at different stages of their life process has revealed that warming waters could impede reproduction in up to 60% of species.

Saltwater and freshwater fish are most sensitive to heat as spawning adults and embryos, researchers at the Alfred Wegener Institute and the Helmholtz Centre for Polar and Marine Research found.

With medium-level human-caused climate change expected by the end of the century, the world’s oceans, rivers and lakes will be too hot for about 40% of the world’s fish species in the spawning or embryonic life stages, said a study in the journal Science, published Thursday.

It means climate change could render them extinct or force species to change how and where they live and reproduce.

Biologists compiled data on the temperature tolerance of 694 fish species and analyzed the temperature ranges within which fish can survive in several capacities: as adults ready to spawn, as embryos in eggs, as larvae, and as adults outside the spawning season, the researchers said in a statement.

This was the first time biologists had studied life stages besides adults, the Associated Press noted. In adult fish, 2% to 3% of the species would be in the too-hot zone in the year 2100 with similar projected warming. The more detailed data show that fish are much more vulnerable to warming climate than previously thought.

“Our findings show that, both as embryos in eggs and as spawning adults, fish are far more sensitive to heat than in their larval stage or as adults outside the spawning season,” said lead author and Wegener institute marine biologist Dr. Flemming Dahlke in a statement. “On the global average, for example, adults outside the mating season can survive in water that’s up to 10 degrees Celsius warmer than spawners or fish eggs can tolerate.”

The study showed that each degree of warming in Celsius means more trouble for the world’s fish stocks, the researchers said. But there is a chance to save many of them.

“If we human beings can successfully limit climate warming to 1.5 degrees Celsius by mid-century and beyond, only 10% of the fish species we investigated will be forced to leave their traditional spawning areas due to rising temperatures,” said Wegener institute biologist and study co-author Professor Hans-Otto Portner.

However, if greenhouse-gas emissions remain high and average warming comes in at 5 or more degrees Celsius, up to 60% of species could be endangered, the researchers said. This could lead to behavioral changes, or even extinction.

“If climate change continues unchecked, we will probably see big changes in the species composition of our ecosystems,” Dahlke told CNN. “When species can no longer reproduce in their traditional habitats, they have to either go into deeper water or further north if possible, or become locally extinct if they’re unable to do that.”

The findings give a much more detailed picture of warming’s effect on fish populations than has been previously available and has grave implications for the approximately 3 billion people whose primary protein source is seafood, CNN reported.

“With spawning fish and embryos most sensitive to warming waters, it means fish populations won’t be able to replace themselves,” Rutgers University ecologist Malin Pinsky, who wasn’t part of the study, told the Associated Press. “Without reproduction and offspring, we have no fish, no fishing and no fish on our plates.”

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