/ 5 June 2023

Rising sea temperatures push fish to Earth’s poles to stay cool

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Photo by Khaled DESOUKI / AFP)

Rising sea temperatures are causing marine fish to seek cooler waters near the Earth’s poles, a new study has found.

Researchers from the University of Glasgow analysed worldwide data on marine fish changes in recent years, showing how fish populations in the oceans are responding to warming in the oceans.

Their latest study, published in the journal Global Change Biology, has identified that, in response to ocean warming, many marine fish populations are shifting toward the Earth’s poles or are moving to deeper waters, all in a bid to stay cool.

The study examined data on 115 species spanning all major oceanic regions, totalling 595 marine fish population responses to rising sea temperatures.

The temperature of the surrounding water affects critical functions such as metabolism, growth and reproduction. Marine species also often have a narrow liveable temperature range making even small differences in the water impossible to cope with. 

As a result, marine life changes caused by global warming have been up to seven-fold faster than animal responses on land. “As marine temperatures are forecasted to continue rising, the ability to predict fish redistributions will be vital to protect ecosystem functions, maintain food security, and other contributors to human well-being,” the study said.

Over the past century, global warming has had a substantial effect on marine ecosystems, with fish species disappearing from some locations. In some cases, they may be able to adapt and change aspects of their biology to adapt to warmer conditions. In many cases, however, a change in the geographical range may be the only means of coping with rapid warming. 

“We observed a striking trend wherewith species living in areas that are warming faster are also showing the most rapid shifts in their geographical distributions,” said the study’s lead author, Carolin Dahms, of the School of Biodiversity, One Health and Veterinary Medicine at the University of Glasgow, in a statement.

It’s possible that the rate of warming in some regions may be too fast for fish to adapt, and so relocating may be their best coping strategy, she said. “At the same time we see that their ability to do so is also impacted by other factors such as fishing, with commercially exploited species moving more slowly.”

Unintended consequences

While relocation to cooler water may allow these species to persist in the short-term, it is not yet known how food-webs and ecosystems will be affected by these changes, said Shaun Killen, the study’s senior author at the University of Glasgow. 

“If the prey of these species don’t also move, or if these species become an invasive disturbance in their new location, there could be serious consequences down the road.”

How these climate responses are measured and reported matters too, they said, noting how while current literature is biased towards northern, commercially important species, in the future more research from some of the most rapidly changing ecosystems such as in the global south will be needed to improve the understanding of how the oceans will change.

Their study described how “very few or no studies” could be identified from some of the most biodiverse regions such as Southeast Asia, South America and Africa, which highlights the “pressing need to expand research on climate responses in marine fish in face of increasing climate change pressures”.