Oceans that are warming due to climate change yield fewer fish

Finding the fish is going to get harder as climate change continues to heat up the world’s oceans. Increasing ocean temperatures over 80 years have reduced the sustainable catch of 124 fish and shellfish species — the amount that can be harvested without doing long-term damage to the populations — by a global average of 4.1 percent, a new study finds.

Overfishing has exacerbated that decline, the researchers say. In some parts of the world, such as the heavily fished Sea of Japan, the decrease in sustainable catch is as high as 35 percent.

The study, in the March 1 Science, examined changes from 1930 to 2010 in 235 fish and shellfish populations scattered across 38 ocean regions. On average, Earth’s surface ocean temperatures have increased by about half a degree Celsius in that time, although temperature changes vary from location to location.

About 8 percent of the fish and shellfish populations studied saw losses as a result of the ocean warming, while about 4 percent of the populations increased in that time. That’s because certain species, such as black sea bass along the northeastern U.S. coast, have thrived in the warmer waters. But with continued warming those gains are likely to evaporate, as even those fish reach their heat threshold, says Christopher Free, a quantitative ecologist at the University of California, Santa Barbara, who led the work while he was at Rutgers University in New Brunswick, N.J.

With some 3.2 billion people worldwide currently relying on seafood as a source of protein, the findings highlight the urgent need for fisheries to take into account how climate change is shifting populations in the sea.