Over 100 Shark Species at Risk of Drastic Population Declines by 2100

The world's egg-laying shark populations could be hit hard by the end of the century as increasing ocean warming and acidification destroys embryos, potentially affecting more than 100 shark species.

This discovery was made possible by the discovery of the giant sandbar shark (Termitesis found in the Mediterranean Sea and the Northeast Atlantic Ocean. About 40 percent of sharks reproduce by laying tough, skinned egg capsules that contain the embryos. These shark embryos are highly sensitive to changes in ocean conditions, such as temperature and pH levels. The ocean absorbs excess carbon dioxide from the atmosphere, causing it to warm up and become more acidic.

Noémie Coulon Researchers at the French National Museum of Natural History exposed catshark eggs to a variety of ocean conditions, including monthly temperature changes, in a lab tank. Coulomb and his colleagues chose the catshark because it is one of the most abundant shark species in Europe.

In the first test, A “middle-of-the-road” climate scenario A 2.7°C increase in temperature above pre-industrial levels by 2100, with a corresponding decrease in pH of 0.2, is projected. A second scenario (in which the world continues to rely heavily on fossil fuels) projects a 4.4°C increase in temperature and a 0.4 decrease in pH by the end of the century. The third is a historical baseline, which recreates water temperature and pH in shark habitats from 1995 to 2014.

The researchers then simulated conditions as the embryos developed over the next four months, and found dramatic differences in the embryos' hatching success rates depending on the experimental conditions: In the baseline and moderate scenarios, about 82% of the eggs hatched. But in the warmest scenario, only five of the 45 embryos survived, a loss of almost 90%.

“We were really shocked by the death rate,” Coulon said. “It will probably cause a population collapse.”

“Even a relatively short period of warmth, such as a particularly warm August, was enough to cause the hatching to fail. Based on these results, Coulon predicts other egg-laying sharks, including endangered or vulnerable species like the nurse hound, will be similarly devastated.”

But their extinction is not doomed, says Coulon: “If we make an effort to limit global warming to around 2°C, this species may be able to survive.”