Fish are growing to only half their average body mass according to a study published this week in the Proceedings of the National Academy of Sciences. What’s more, smaller species of fish are making up more and more of the European fish stock- and the study points the finger at global warming.
“Size is a fundamental characteristic that is linked to a number of biological functions, such as fecundity-the capacity to reproduce,” said Martin Daufresne, author of the study, who works at the Cemagref Public Agricultural and Environmental Research Institute in France.
So what does this mean?
Well, fewer eggs to start with. A smaller fish tends to produce fewer eggs and of course less food. Put those together and you have bad news for ecosystems and food chains. Thought of in economic terms, this means less food (supply) and smaller portions for a growing population (demand).
Not only are the fish shrinking- as the water gets warmer, they’re moving. Research has shown that fish are shifting their geographic range as well as migration and breeding routes and patterns. Warmer water tends to mean smaller fish. Strike two.
Daufrensne used long-term surveys to study fish, bacteria and plankton in rivers and streams as well as the North and Baltic Sea.
Over 30 years of study:
50% average body mass loss for each species.
60% average size lost in overall fishing stock.
Why? A decrease in the average size at age and an increase in the proportion of juveniles and small species, according to Daufresne.
“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,” said Daufresne. He also said that even though both commercial and recreational fishing had an impact, the study found that it “cannot be considered as the unique trigger.” I take that to mean that global warming can’t be considered the unique trigger either, but if you put overfishing and global warming on the same team, it may be time to buy stock in sardine tins.
“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.