Ocean Warming Is Shrinking Fish Size
October 1, 2012

Warming Oceans Creates Smaller Fish And Shrinks Fish Stocks

Brett Smith for redOrbit.com - Your Universe Online

New research by a team of North American scientists indicates that warmer water may cause shrinkage in average fish size and populations of fish stocks.

"We were surprised to see such a large decrease in fish size," said William Cheung, a professor at the University of British Columbia and lead author of a report on the team´s research that was published in the journal Nature Climate Change. "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 added.

According to the report, the average body weight of 600 types of fish is expected to shrink 14 to 24 percent from 2000 to 2050 “under a high-emission scenario.”

The report also said that warmer marine temperatures will drive many fish north in search of cooler waters.

Both of these effects are linked because fish require oxygen for their metabolism and, as the average temperature increases, the water retains less oxygen.

"It's a constant challenge for fish to get enough oxygen from water to grow, and the situation gets worse as fish get bigger," explained study co-author Daniel Pauly, a professor with UBC's Sea Around Us Project. "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."

Smaller fish sizes could also have unforeseen impacts on the overall population, like affecting the ability of these fish to reproduce viable offspring.

"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," Alan Baudron, from the University of Aberdeen, UK told BBC News.

Based on metabolic equations and migration models, the study said fish living in the Indian Ocean were likely to shrink by 24 percent, Atlantic fish by 20 percent, and Pacific fish by 14 percent. The study also said most fish populations would migrate 17 to 22 miles closer to the poles from 2000 to 2050.

The researchers noted that many other factors are expected to negatively impact the fish that feed the world. Overfishing has been a strain on these fish for years and the growing population is expected to increase that pressure.

The growing population is also expected to increase man´s overall carbon footprint, which not only fuels climate change–it can also acidify the oceans. This acidification could severely impact many species that form the foundation of the ocean´s food webs.

According to the scientists, this study underlines the need to reduce carbon emissions and develop strategies to mitigate the damage already being seeing. In sounding the alarm, they also cite previous studies that project the tropics will suffer a high rate of local extinction and a reduction in maximum catch potential.