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Fish likely to be shrunk by climate change, scientists warn


Fish are likely to shrink as climate change intensifies, bringing with it lower levels of oxygenation and other factors, according to a new study.

Average reductions of up to 24 per cent will take place by 2050, with fish in tropical and temperate zones being affected, the study found.

Scientists warned that a consequence of smaller fish, both individually and in the total combined weight, is likely to place further pressure on fisheries and food supplies at a time when the human population reaches record levels.

The findings were made by researchers from Canada and the US who created a model to reveal what would happen to marine fish as greenhouse gases emissions rise, causing changes in distribution, abundance and in the oxygen levels of the water.

“We were surprised to see such a large decrease in fish size,” said Dr William Cheung, of the University of British Columbia, Canada. “Marine fish are generally known to respond to climate change through changing distribution and seasonality. But the unexpectedly big effect that climate change could have on body size suggests that we may be missing a big piece of the puzzle of understanding climate change effects in the ocean"

Professor Daniel Pauly, his co-author and the director of the Sea Around Us Project at British Columbia, added: “It’s a constant challenge for fish to get enough oxygen from water to grow, and the situation gets worse as fish get bigger. A warmer and less-oxygenated ocean, as predicted under climate change, would make it more difficult for bigger fish to get enough oxygen, which means they will stop growing sooner.”

Fish growth is limited by the availability of oxygen and the study found “unexpectedly large” changes in the size to which they are likely to grow.

The researchers assessed more than 100 different species of fish and found that the weight of species assemblages will fall by 14 to 24 per cent on average. The weight of individual fish is likely to fall on average by 5 to 39 per cent.

“This study indicates that the consequences of failing to curtail greenhouse-gas emissions on marine ecosystems are likely to be larger than previously expected,” the researchers said in their report, published in the journal Nature Climate Change.

“Other human impacts, such as overfishing and pollution, are likely to further exacerbate such impacts. Consequently, these changes are expected to have large implications for trophic interactions, ecosystem functions, fisheries and global protein supply.”


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