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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.

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

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 published in the journal Science.

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

Biologists compiled data on the temperature tolerance of 694 fish species and analyzed the 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.

This was the first time biologists had studied life stages besides adults. In adult fish, 2% to 3% of the species would be in the too-hot zone in the year 2100 with similar projected warming.

“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. “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 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 midcentury and beyond, only 10% of the fish species we investigated will be forced to leave their traditional spawning areas due to rising temperatures,” said Professor Hans-Otto Portner Wegener Institute biologist and study co-author.

However, if 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.

The findings give a much more detailed picture than has been previously available and have 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 said. “Without reproduction and offspring, we have no fish, no fishing and no fish on our plates.”