In 80 Years, Warming Oceans Have Cut Multiple Fisheries' Productivity By 15-35%

Marine fish around the world are already feeling the effects of climate change—and some are reeling, according to the first large analysis of recent trends. Rising sea temperatures have reduced the productivity of some fisheries by 15% to 35% over 8 decades, although in other places fish are thriving because warming waters are becoming more suitable. The net effect is that the world’s oceans can’t yield as much sustainable seafood as before, a situation that is likely to worsen as global warming accelerates in the oceans.

A silver lining is that the research suggests well-managed fisheries are more resilient in the face of rising temperature, says Rainer Froese, a marine ecologist with the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, who was not involved in the work. “We have to stop overfishing to let the gene pool survive, so that [the fish] can adapt to climate change,” he says. “We have to give them a break.”

As cold-blooded animals, fish mirror the temperature of the water they swim in. When the water gets too warm, the enzymes they use for digestion and other functions are less efficient, impairing growth and reproduction. In addition, warm water contains less oxygen, a further stressor.

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So what has climate change done to sustainable fishing? Out of 235 stocks, Free and his colleagues found a few winners. Nine stocks had become on average 4% more productive. These stocks are in places where rising temperatures have made too-cold water more suitable for fish, such as far north and south of the equator. Off the coast of Newfoundland and Labrador in Canada, for example, the maximum sustainable yield has increased by 14% since 1930. And fishing there could get even better. According to the new research, the productivity of Greenland halibut will increase 51% with each degree Celsius of warming. That’s like getting a big, fat boost to the interest rate on your saving account. This local good news is outweighed by 19 stocks elsewhere that are on average 8% less productive than before. Many of these are around northern Europe and Japan, and they will likely continue to decline as their environment continues to heat up. Boats chasing Atlantic cod in the Irish Sea face a particularly grim future: The maximum sustainable yield of this stock will shrink by 54% for each additional degree of warming, the team reports today in Science.

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https://www.sciencemag.org/news/2019/02/warming-oceans-are-hurting-seafood-supply-and-things-are-getting-worse