Global warming is going to start shrinking fish

Even if we manage to stem the tide of climate change over the next few decades, it's likely the Earth's biosphere will be dramatically changed. And for marine life, that could mean we'll start seeing some seriously tiny fish.

That's the finding of researchers at the University of British Columbia, who used computer modeling to determine the future maximum body weights of over 600 different fish species. It's based on a simple chain of events — if global temperatures rise, then ocean waters will become warmer. That in turn tends to deplete the amount of oxygen available for fish to breathe.

We know from previous studies that that could change the geographic distribution of fish species, as currently tropical fish might swim into more temperate zones just to find waters that are still the right temperature for them. The oxygen depletion has also been shown to have a likely effect on fish reproductive patterns, and this later computer simulation suggests fish size will also be affected, as maximum body weight could decrease 14 to 20% between now and 2050. Lead author William Cheung discusses the results in a statement:

"We were surprised to see such a large decrease in fish size. 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."

In a subsequent interview with the BBC, Cheung elaborated on what fish species might look like four decades from now. Basically, we're talking smaller and at higher latitudes:

"Rising temperatures directly increase the metabolic rate of the fish's body function. This leads to an increase in oxygen demand for normal body activities. So the fish will run out of oxygen for growth at a smaller body size. So in, say, the North Sea. one would expect to see more smaller-body fish from tropical waters in the future...Our study shows that climate change can lead to a substantial decrease in the maximum body weight of fish. We need to look more closely at the biological response in the future."

For more on this story, check out the BBC News article and the original paper over at Nature Climate Change.

Image by laszlo-photo on Flickr.