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The climate changes made it so that the fish will move to cooler waters, or try to adapt to their local environment.
We already knew that the warming of the waters will create against lethal conditions for many adult fish. The authors of a new study now indicates that the effect will be even more pronounced for the embryos and the individuals in reproduction. As a result, even if the humanity reached its targets in the current climate, more than one-third of the fish species will not be adapted, at the end of the century, the environment that they occupy today.
The team based in Germany has found that there is a “funnel effect thermal” in the life cycle of the majority of species of fish. While the larvae and adult non-spawners resist relatively well to temperature increases, the embryos and adults during the breeding season are much more sensitive : they can tolerate, on average, a window temperature by less than 20 °C.
The researchers arrived at this conclusion by analyzing the already existing studies on 694 species of marine fish and fresh water. To fill some of the missing data, they extrapolated the values of other species genetically close. The journal Science publishes the results in its edition of Friday.
“The greater sensitivity of eggs and breeding adults means that marine fish and freshwater live much closer to their limits hot springs that we thought we did until now,” judge Jennifer Sunday, a biologist from McGill University, as a sign of analysis accompanying the publication in the journal.
In the scenario where the concentration of CO2 in the atmosphere reach 1,000 parts per million by 2100, 60% of the species can no longer fulfill their entire life cycle in their current environment. In the scenario where the CO2 concentration returns to the level of 2005 to the end of the century, only 10% of species would live this drama.
“Very clearly, several species of fish, as well as people whose diet is based on fish healthy, would benefit from an intensification of the efforts to stabilize the global warming at 1.5 °C, or even less,” write Flemming Dahlke and his colleagues of the Alfred Wegener Institute for polar research and marine.
All fish can survive in a limited range of temperatures. Beyond or below these thresholds, they have trouble controlling the level of oxygen in their body — or, in other words, they have trouble breathing. When it is too warm, their metabolism consumes too much oxygen ; when it is too cold, their body can’t carry enough oxygen to their tissues.
Since the embryos have a cardiovascular system-respiratory system is still developing, they are resistant to temperature differences of less than large. The adults that produce eggs or sperm must supply a body more massive, without the need for a better oxygen supply.
In practice, the climate changes made it so that the fish will move to cooler waters, or try to adapt to their local environment.
For populations which remain in place some mechanisms that will allow them to compensate — at least temporarily — the death of embryos overheating, ” explains Jennifer Sunday. “Ecologists know very well that, even in normal times, each of the eggs of a fish does not become an adult,” she said in an interview. We will not see may not be a decline in the populations immediately, but, one day, the effect may be sudden and dramatic. “
As for the populations that will be forced to move, nothing indicates that they will find a new suitable habitat. “Is it that their food is there ? Choose their spawning habitat as a function of temperature, or because they find there good food ? A new predator will eat their eggs ? It is very difficult to predict, ” says Ms. Sunday.
We will not see may not be a decline in the populations immediately, but, one day, the effect may be a sudden dramatic
— Jennifer Sunday
The authors of the article published on Friday warn that their estimates are probably conservative, because they do not consider the deoxygenation, acidification, and increased frequency of episodes of extreme temperatures that climatologists predict for the next decades.
In addition, the fish may have trouble feeding. Last year, an international collaboration of researchers, including several Canadians, believed that each degree of warming amputerait the animal biomass of the oceans of 5 %. They associated this decline with a warming of surface waters, limiting the input of nutrients from the deeper layers.