Warmer waters from climate change expected to shrink fish: UBC researchers

A new study done by the researchers at the University of British Columbia (UBC) says fish are expected to shrink in size by 20 to 30 per cent on average if water temperatures continue to rise due to climate change. Even more so for other species.

Dr. Daniel Pauly, the study’s lead author and principal investigator for UBC’s Institute for the Oceans and Fisheries, explains that marine life is redistributing to the North and South poles to escape rising water temperatures.

However, not all fish can escape the warm waters.

“A cold-blooded fish when you increase the temperature needs more oxygen because its metabolic rate goes up,” said Pauly.

The amount of oxygen a fish requires greatly increases as it grows into adulthood because their body mass becomes larger.

The warmer the water, the less oxygen it contains. If there was accessible oxygen in the water, they still couldn’t absorb as much as they need.

The surface area of the gills where oxygen is obtained doesn’t grow as the same pace as the rest of the body, which creates an issue.

“If you increase oxygen needed by a body and you don’t increase the surface of the gills that supply the oxygen you have a problem,” Pauly explained.

The development of larger gills to absorb oxygen is an evolutionary process that takes a long time. Researchers say this forces fish to grow to a smaller size to be able to fulfill the small amount of oxygen available.

“We predict fish will get smaller and smaller but we don’t only predict it, we observe it because there are already studies that show this phenomenon to have occurred,” Pauly said.

Above all, the most affected are tuna and other big fish because their swift swimming skills require the greatest amount of energy and oxygen.

As a result, researchers say, the overall biomass of the oceans will shrink, reducing the overall amount of fish that can be caught by 30 per cent.


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