Some sharks can respire by pumping water over their gills through opening and closing their mouths while at rest on the bottom. Sharks attack their prey in whichever way is most convenient, and they can protrude their jaws to bite prey items in front of their snouts. Sharks eat periodically depending upon their metabolism and the availability of food. Most sharks don't appear to be especially interested in the blood of mammals as opposed to fish blood. Most sharks prefer to eat certain types of invertebrates, fish and other animals.
Some sharks eat mainly fish.
Others eat other sharks or marine mammals. Some sharks are even plankton-eaters. Whale sharks, which are the largest fish that ever lived, are plankton feeders like the great whales, thus the name. Great whites are relatively uncommon large predators that prefer cooler waters. In some parts of their range, great whites are close to being endangered.