Sardines are a key element in the marine food chain, and are one of the most caught fish in the world, but since the mid-2000s, their size has decreased dramatically, and in the Mediterranean Sea has decreased from 15 to 11 centimeters on average, according to the institute, which showed His research is that these changes are not caused either by hunting, nor by natural predators, nor by a virus, but rather by the diet of these fish.
Jean-Marc Fromantin, a researcher at the French Research Institute for the Exploitation of the Sea in Cite, explained that “the satellite images clearly show a decrease in the amount of microalgae up to 15 percent in the mid-2000s,” noting also to a decrease in the size of planktonic cells.
“These shifts are the result of significant regional environmental changes, which are manifested in the decline in nutrients brought by the Rhone River, changes in the atmospheric and ocean circulation, and an overall increase in temperature of 0.5°C over an average of 30 years due to climate change,” the institute explained.
An experiment was also conducted within the framework of this study, which consisted of distributing 450 sardines to 8 tanks to test the effect of food size and quantity on their ability to survive and grow.
“We were surprised by the very large effect of the size of the feed,” said Claire Sarro, a former researcher at the Institute and current at the French National Center for Scientific Research, explaining that “sardines that receive small-sized feed need twice their size to grow like sardines whose food sources are large.”
Small feeds cause sardines to eat their prey by “filtering”, through the gills, forcing them to swim continuously for a fairly long time.
If the feed is large, the sardines will eat their prey one by one, which requires a much shorter swimming time and therefore requires less energy.
And when sardines were given more and more feed, they regained a size similar to that caught before 2008.
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