Fish are expected to shrink by up to 30 percent due to rising ocean temperatures, a direct result of climate change, according to a new study by researchers at the University of British Columbia. The study, entitled “Sound physiological knowledge and principles in modeling shrinking fishes under climate change,” was published last week in Global Change Biology.
This phenomenon is due to the inability of fish to regulate their own body temperatures, explains William Chung, director of science for the Nippon Foundation — University of British Columbia Nereus Program and study co-author.
“When their waters get warmer, their metabolism accelerates and they need more oxygen to sustain their body functions,” explains Cheung. “There is a point where the gills cannot supply enough oxygen for a larger body, so the fish just stops growing larger.”
Gills already grow less quickly than the fish themselves, according to the researchers, which exacerbates this problem.
The researchers estimate that the size of fish will decrease by 20 to 30 percent for every degree Celsius increase in water temperature, though they also note that certain fish will be more heavily affected than others, such as tuna, which are fast moving and require more energy and thus more oxygen.
"Lab experiments have shown that it's always the large species that will become stressed first," says lead author Daniel Pauly, a professor at the university's Institute for the Ocean and Fisheries, and principal investigator for "The Sea Around Us." "Small species have an advantage, respiration-wise."
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The researchers estimated that potential catch loss could amount to 3.4 million metric tons for each degree Celsius of atmospheric warming, with some parts of the world, such as the tropics, experiencing even greater losses.
These changes will certainly have profound effects on marine food webs, according to the scientists, though these consequences are difficult to predict precisely.
“Basically, big fish eats small fish,” Cheung says. “So, changes in body size may alter food web interactions and structure, affecting ecosystem functions and services.”
Many experts around the world have already confirmed that these findings are in line with their own observations.
"It is absolutely an inevitability that as fish grow heavier they will eventually reach a point where oxygen intake does not match their metabolic demand," Nick Dulvy, a marine biologist at Simon Fraser University, tells National Geographic.
In 2013, Pauly and Cheung published a similar study in Nature Climate Change that was heavily criticized by researchers in Norway and France for being overly simplistic. The new study, reports National Geographic, uses “more sophisticated models” to confirm the previous theory and even proves that some of the conclusions drawn in 2013 underestimated the severity of the issue.
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