An estimated 60 percent of fish species will struggle to reproduce in their current spawning habitats by 2100 under worst-case climate scenarios, according to a new study of nearly 700 salt and freshwater species published in the journal Science. The research argues that previous studies, which focused solely on adult fish, underestimate the impact climate change will have on economically and ecologically important species.
As temperatures rise, fish — like humans — need more energy to survive, which requires them to take in more oxygen. But embryos don’t have gills that allow them to take in additional oxygen. And spawning fish already require extra oxygen to support the production of eggs or sperm cells; warming temperatures just add to this strain.
“Our findings show that, both as embryos in eggs and as adults ready to mate, fish are far more sensitive to heat than in their larval stage or sexually mature adults outside the mating season,” Flemming Dahlke, a marine biologist at the Alfred Wegener Institute and lead author of the new study, said in a statement. “On the global average, for example, adults outside the mating season can survive in water that’s up to 10 degrees Celsius warmer than adults ready to mate or fish eggs can.”
Dahlke and his colleagues found that if global warming is limited to 1.5 degrees Celsius by 2100, only 10 percent of fish species would either have to move to new, cooler spawning grounds or experience reproductive failure. If greenhouse gas emissions remain high, however, and warming reaches 5 degrees C or more, up to 60 percent of fish species would be impacted.
Some species may be able to adapt, the researchers said. But many others will not, such as fish living in rivers and lakes, where size or geographic location limit their ability to move to new spawning grounds. And the loss of some critical species, such as Atlantic cod in the North Sea, could drive massive ecosystem shifts that result in the loss of others.
“Humankind is pushing the planet outside of a comfortable temperature range and we are starting to lose suitable habitat,” Hans-Otto Pörtner, a climatologist at the Alfred Wegener Institute and coauthor of the study, told The Guardian. “It’s worth investing in the 1.5-degree C goal.”