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Explained: What will happen to fish as oceans warm?

Several species were noted to migrate poleward or to deeper waters to stay in their ideal temperature range.

fish and climate changeGlobal warming could limit the aerobic capacity of fish, impairing their physiological performance in the future (Wikimedia Commons)

The latest Intergovernmental Panel on Climate Change (IPCC) report has warned that ocean warming will continue over the 21st century and is likely to continue until at least the year 2300 even if we minimise carbon emissions.

“The amount of ocean warming observed since 1971 will likely at least double by 2100 under a low warming scenario and will increase by 4-8 times under a high warming scenario,” warns the report, adding that human influence is the main driver of the warming.

This warming can help create both anoxic (waters that have no dissolved oxygen) and hypoxic (low oxygen concentration) zones. The report adds that these oxygen-deficient areas are expected to persist for thousands of years.

So, what will fish do when their habitat becomes warm?

Previous studies have noted that warming oceans can cause stress, decrease the range, increase diseases and even wipe out many commonly eaten fish. Last year, a study noted that future ocean warming and acidification may drag down the commercial Arctic cod fishery by 2100.

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Several species were noted to migrate poleward or to deeper waters to stay in their ideal temperature range. A study published in April found that the total number of open-water species in tropical marine zones declined by about half in the 40 years up to 2010.

Honey, I shrunk the fish

A new research published on Monday suggested that fish like sardines, pilchards and herring will become smaller in size and not be able to move to better environments. Professor Chris Venditti, an evolutionary biologist at the University of Reading, and co-author of the study, said in a release: “With sea temperatures rising faster than ever, fish will very quickly get left behind in evolutionary terms and struggle to survive. This has serious implications for all fish and our food security, as many of the species we eat could become increasingly scarce or even non-existent in decades to come.”

Though the team studied Clupeiforms – the order of ray-finned fish which includes anchovies, Atlantic herring, Japanese pilchard, Pacific herring, and South American pilchard – they note that the findings have implications for all fish.


Previous studies have also noted various fish species shrinking in size. In March, researchers noted that warming oceans can also cause baby sharks to be born smaller. The team raised sharks under either 27 degrees Celsius or 29 degrees Celsius and 31 degrees Celsius. They found that the sharks reared in the warm waters weighed less and had low metabolic performance than those raised in lower temperatures.

Struggle for survival

By studying the metabolic rates of 286 species of fishes, researchers noted in January that even larger fish will struggle to survive.

“Our data suggest that, as temperature increases, the demand for oxygen of many fish species will exceed their capacity to extract oxygen from the environment through their gills,” explains Juan Rubalcaba, lead author of the paper, in a release. “As a result, the aerobic capacity of fish decreases in warming waters, and this reduction may be more important in larger fishes. This tells us that global warming could limit the aerobic capacity of fish, impairing their physiological performance in the future.”


Which fish will survive climate change?

In May, a paper published in Molecular Ecology noted that the threespine stickleback fish can adapt rapidly to changes. The team studied the genes of threespine stickleback fish before and after seasonal changes. “The modern version of Darwin’s idea of evolution by natural selection posits that organisms with genes that favour survival and reproduction will tend to leave more offspring than their peers, causing the genes to increase in frequency over generations,” says lead author Alan Garcia-Elfring in a release.

His team discovered evidence of genetic changes driven by seasonal changes. “The findings are important because they suggest that we may be able to use the genetic differences that evolved in the past as a way to predict how populations may adapt to environmental stressors like climate change in the future,” he says.

First published on: 13-08-2021 at 15:13 IST
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