Fish have lost half their average body mass and smaller species are making up a larger proportion of European fish stocks as a result of global warming, a study published yesterday has found.
“It’s huge,” said study author Martin Daufresne of the Cemagref Public Agricultural and Environmental Research Institute in Lyon, France. “Size is a fundamental characteristic that is linked to a number of biological functions, such as fecundity — the capacity to reproduce.”
Smaller fish tend to produce fewer eggs. They also provide less sustenance for predators — including humans — which could have significant implications for the food chain and ecosystem.
A similar shrinking effect was recently documented in Scottish sheep and Daufresne said it was possible that global warming could have “a significant impact on organisms in general.”
Earlier research has already established that fish have shifted their geographic ranges and their migratory and breeding patterns in response to rising water temperatures. It has also been established that warmer regions tend to be inhabited by smaller fish.
Daufresne and his colleagues examined long-term surveys of fish populations in rivers, streams and the Baltic and North seas and also performed experiments on bacteria and plankton. They found the individual species lost an average of 50 percent of their body mass over the past 20 years to 30 years, while the average size of the overall fishing stock had shrunk by 60 percent.
This was a result of a decrease in the average size-at-age and an increase in the proportion of juveniles and small-sized species, Daufresne said.
“It was an effect that we observed in a number of organisms and in a number of very different environments — on fish, on plankton, on bacteria, in fresh water, in salt water — and we observed a global shrinking of size for all the organisms in all the environments,” Daufresne said in a telephone interview.
While commercial and recreational fishing did impact some of the fisheries studied, it “cannot be considered as the unique trigger” for the changes in size, the study published in the Proceedings of the National Academy of Sciences found.
“Although not negating the role of other factors, our study provides strong evidence that temperature actually plays a major role in driving changes in the size structure of populations and communities,” the study concluded.