One quarter of all sharks and rays are threatened with extinction, according to a new study published in the open-access journal eLife. The paper analyzed the threat and conservation status of 1,041 species of chondrichthyans—the class of fish whose skeletons are made of cartilage instead of bone which includes sharks, rays, skates and chimaeras—and found this group to be among the most threatened animals in the world.
Would one quarter of mankind extinct fix this?
I don't think so, If the remaining people will continue to overfish and pollute like we do now. The population would have to drop way more than that in order to have any effect.