Oceans’ fever means fewer fish | Science News for Students

Oceans’ fever means fewer fish

Since 1930, some regions have seen a 35 percent drop in individuals that can be caught without harming fisheries
Apr 11, 2019 — 6:30 am EST
a pile of haddock fish

Increasing ocean temperatures have caused populations of many fish and shellfish to plummet. As a result, the amount that can be caught without depleting fish populations has declined by an average of 4.1 percent worldwide.


Finding fish is going to get harder as climate change continues to heat the world’s oceans. A new study finds that warming seas over the past 80 years have reduced the sustainable catch of 124 species of fish and shellfish.

Sustainable catch refers to the amount that can be harvested without doing long-term damage to the health of populations of some species.  

Overfishing has made that decline worse, researchers say. Overfishing refers to catching so many fish that the size of the population falls. In some parts of the world, such as the heavily fished Sea of Japan, the decrease is as high as 35 percent. That’s a loss of more than one in every three fish.

Researchers examined changes in 235 populations of fish and shellfish between 1930 and 2010. Those fish populations were scattered across 38 ocean regions. Temperature changes vary from one ocean site to another. But on average over that time, Earth’s sea-surface temperatures have risen by about half a degree Celsius (0.9 degree Fahrenheit).

On average, that warming has caused the sustainable catch to drop by 4.1 percent, the study found. About 8 percent of the fish and shellfish populations the team studied saw losses as a result of the ocean warming. About 4 percent of the populations increased. That’s because certain species have thrived in warmer waters. One example is the black sea bass. It dwells along the northeastern U.S. coast. But as warming continues, even these fish will reach their limit, says Christopher Free. He works at the University of California, Santa Barbara. He led the work while he was at Rutgers University in New Brunswick, N.J.

His team shared its findings March 1 in Science.

About 3.2 billion people worldwide rely on seafood as a source of food. That means it’s urgent for commercial fishing fleets and regulators to consider how climate change is affecting the health of all of those fish in the sea.

Power Words

(more about Power Words)

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

commercial     (in research and economics) An adjective for something that is ready for sale or already being sold. Commercial goods are those caught or produced for others, and not solely for personal consumption.

population     (in biology) A group of individuals from the same species that lives in the same area.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

sustainable     An adjective to describe the use of resources in a such a way that they will continue to be available long into the future.

Further Reading

Journal:​ ​​C.M. Free et al. Impacts of historical warming on marine fisheries productionScience. Vol. 363, March 1, 2019, p. 979. doi: 10.1126/science.aau1758.