Within the next 50 years, bluefin tuna are at risk of disappearing from the Mediterranean, due to the unbearable temperatures that will reach our waters. This is supported by a study from the University of Southampton, published in Nature Communications.
Bluefin tuna live and reproduce on both sides of the Atlantic, and populations on the eastern side spend their first year of life in the Mediterranean, where they find a favorable environment to grow. Once they reach adulthood, a year old, tuna leave the Mediterranean and swim across the Atlantic, returning to their place of origin only when it's time to spawn. The problem is that, during this first year of life, bluefin tuna are particularly sensitive to water temperature.
If it gets too hot they suffer, to the point where they leave the area in search of cooler places. To find out what this threshold of tolerance is, the Southampton team used an innovative method: the analysis of otoliths, small "pebbles" made of calcium that are found behind the brains of fish and are used by these animals to maintain balance.
However, otoliths can also be used to measure changes in tuna metabolism over time. By cross-referencing this data with the temperatures of the waters in which they swim, it is possible to calculate when the sea becomes too warm for these fish. The result is 28°C, which is the temperature most of the Mediterranean will be at within the next fifty years. Therefore, it is very likely that over the years the bluefin tuna will no longer return to the Mediterranean to reproduce and will choose new areas to serve as nurseries: for example the Bay of Biscay, between Spain and France. However, where the waters are used by sardine and anchovy fishermen, the risk is that newly arrived tuna will end up accidentally caught in nets, with serious damage to their populations. (A2 Televizion)
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