Global Warming Has Cascading Effect on Fish Size and Population

Climate change may reduce the size of fish by up to 24 percent and make them smaller, finds a new study.

Researchers used computer models to analyze the impact of global warming on marine ecosystems - mainly the fish species living in tropical regions. They studied over 600 species of fish in oceans across the world and found that the increase in global temperatures will cause the body size of fish species to shrink by 14-24 percent between the years 2000 and 2050.

Increase in global temperatures is mainly caused by the release of greenhouse gases due to human activities. Earlier studies have already explained the effect of global warming in the survival and distribution of marine creatures.

This new study suggests that changes in climate will have a bigger impact than previously thought with the global temperatures projected to cause significant decrease in the body size of fish.

"We were surprised to see such a large decrease in fish size," study's lead author William Cheung, an assistant professor at the University of British Columbia Fisheries Center, said in a news release.

"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," he said.

The research team developed the models based on high emission scenarios set by the Intergovernmental Panel on Climate Change (IPCC). They estimated the changes in the average maximum body weight of individual fish species as well as fish living in a group from the year 2000 to 2050 in the scenario.

They projected that the increase in global temperatures will increase the bottom temperature in the Atlantic, Indian, Pacific, Southern and Arctic oceans to a small extent. Oxygen levels in the sea are also predicted to decline.

Despite the rate of increase in ocean temperature, oxygen levels will be low and it will have a major effect on the growth of the fish species, the researchers wrote. Fish living in oxygen depleted oceans will struggle to grow as they would not get the required oxygen. As a result, they will stop growing sooner and will have a slower growth, and smaller body size.

Based on computer models, experts also suggested that ocean warming will push most of the fish population towards the poles, reducing their average body size.

Reduction in body size will affect the reproductive process of fish. Smaller fish will produce fewer eggs, thus decreasing the birthrate of the fish population. "Smaller individuals produce fewer and smaller eggs which could affect the reproductive potential of fish stocks and could potentially reduce their resilience to other factors such as fishing pressure and pollution," Cheung told BBC News.

Experts suggested that proper steps need to be taken to curb the emission of greenhouse gases and develop strategies so as to adapt to the changes in the marine ecosystem.

The findings of the study, "shrinking of fishes exacerbates impacts of global ocean changes on marine ecosystems", are published in the journal Nature Climate Change.