A ‘significant proportion’ of fish species may soon be unable to mate, forcing them to abandon current spawning areas within a century. As water warms it loses oxygen and raises metabolisms, increasing the bodies demand for oxygen.
This means well-known fish could ‘drown’ in hotter oceans, lakes and streams during the vulnerable stages of their lives.
Our findings show that fish are far more sensitive to heat than in their larval stage or sexually mature adults outside the mating season
Dr Flemming Dahlke
Adult fish preparing to mate become packed with either eggs or sperm.
This places an additional strain on their hearts as they try to supply them with enough oxygen.
Fish embryos inside eggs could also die as they don’t have gills.
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This means they will be unable to get enough oxygen to survive.
Scientists studied the temperature tolerances of 694 species of marine and freshwater fish to establish the impact rising temperatures will have.
They analysed the temperature ranges in which fish can survive at every life stage.
This ranges from an embryo in an egg, larvae and adult, split by during and not during the mating season.
They also analysed predicted temperature changes in spawning areas, to predict what impact this may have.
Dr Flemming Dahlke, first author and biologist at the Helmholtz Centre for Polar and Marine Research said: “Our findings show that fish are far more sensitive to heat than in their larval stage or sexually mature adults outside the mating season.”
If global warming can be limited to 1.5C (2.7F) by the end of the century, the scientists said only ten percent of fish species will be forced further north.
However, current predictions on climate change suggest warming will rapidly exceed this limit.
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A study published this week in Scientific Data warns Earth has already warmed by 1C (1.8F) in the past 150 years, and temperatures will probably to keep rising.
In response to the change, fish will be forced to either adapt through biological evolution, which is likely to take too long, or move closer to the poles.
Dr Dahlke added: “Some species might successfully manage this change.
“But if you consider the fact that fish have adapted their mating patterns to specific habitats over extremely long time frames, and have tailored their mating cycles to specific ocean currents and available food sources.
“It has to be assumed that being forced to abandon their normal spawning areas will mean major problems for them.”
Species inhabiting rivers and lakes have the added problem that they are limited by size and geography.
This makes migrating to deeper waters or areas nearer the poles ‘nearly impossible’.
Any migration of fish species is also expected to cause a drop in productivity, as they adjust to their new habitats.
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