European fish are getting smaller. Over the past two to three decades some varieties have lost almost half of their body weight. And while smaller fish now make up a greater percentage of all fish species, European fish stocks have also shrunk -- by around 60 percent.
This is according to a study by researchers, Martin Daufresne, from the Cemagref Public Agricultural and Environmental Research Institute in Lyon, France, and Ulrich Sommer from the Leibniz Institute of Marine Sciences, Kiel University in Germany. The study was published this week in the journal Proceedings of the National Academy of Sciences.
The researchers looked at long term surveys of aquatic communities in European rivers and streams and in the North and Baltic seas -- they included fish, plankton and bacteria in their study -- and found that, on average, the fish got smaller as average temperatures in the water went up.
"It was an effect that we observed in a number of organisms and in a number of different environments; on fish, on plankton, on bacteria, in fresh water, in salt water. We observed a global shrinking of size for all the organisms in all the environments," study author, Daufresne, told the Agence France Presse news agency on Monday.
The researchers do not believe that other factors, such as over fishing, were the reason. "Although not negating the role of other factors, our study provides strong evidence that temperature actually plays a major role," the study concluded.
The results of this discovery could be far reaching. "It's huge," Daufresne said. Because, "size is a fundamental characteristic that is linked to a number of biological functions, such as fecundity -- the capacity to reproduce." That is, smaller fish lay fewer eggs. Additionally they provide less sustenance for predators -- all of which could have a domino effect that goes right up the food chain and eventually affects humans too.
Climate change has already been shown to have an impact on animals right around the world, with rising temperatures causing changes in migratory patterns and shifts in the timing of major life events among living organisms. And while Daufresne believes global warming plays a role, it's hard to conclude whether rising temperatures might be causing other animals to shrink. Having said that, one recent study published in the journal Science noted that Scottish sheep seemed to be getting smaller as winters got milder.
What is clear to Daufresne though, "is that it's something which seems to happen everywhere. The fact that we observe this common pattern among different systems and among different kinds of organisms means that there is a real effect of the global warming on size."