Global warming 'may lead to smaller fish'

The biggest fish in the sea could be almost 25 per cent smaller by 2050 because of global warming, according to a new study.

Warmer oceans will carry less dissolved oxygen, causing fish to grow to smaller sizes and forcing them to move to cooler waters, the research published in the journal Nature Climate Change claims.

Scientists predict that a rise in global temperatures over the coming decades will cause the average body size of sea fish to decline by between 14 and 24 per cent.

The predication is based on a study of more than 600 species of saltwater fish, including the Atlantic cod and the North Sea haddock.

About half of the shrinkage will be due to changes in the distribution and abundance of fish caused by changes to their environment, and half will be the direct result of living in oxygen-poor water.

Species living in tropical and intermediate-latitude oceans will suffer the most, with an average reduction in weight of more than 20 per cent, according to the study by William Cheung and colleagues at the University of British Columbia in Vancouver, Canada.

While changes in distribution were expected, "we were surprised to see such a large decrease in fish size", Dr Cheung said. "The unexpectedly big effect that climate change could have on body size suggests that we may be missing a big piece of the puzzle in understanding climate change effects."