Do sharks Sleep? Well, This might be true for some species of sharks e.g Big white sharks. But not for all species of sharks. Sharks are cartilaginous fish and eventually lack a swim bladder. So sharks adapt a few methods as solutions to this problem. The powerful pectoral fins of sharks help them to meet dynamic lift. That lift gives them the ability to survive in water. These sharks can freely move through different depths of the ocean. They are not supposed to take a rest. This is to prevent themselves from sinking. In other cases, sharks take advantage of this lack. They adopt bottom-dwelling existence. Like Nurse sharks resting on seafloor and reefs. Similarly, Whitetip reef sharks prefer to sleep stacked on each other.