Several marine mammals are capable of extended dives lasting well over an hour. The record belongs to the elephant seal, which can stay underwater for up to two hours at a time.
Among whales, the sperm whale holds its breath the longest, often making 90-minute dives while hunting in very deep water. Diving mammals slow their heart rate and shunt blood from their extremities to vital organs during deep dives. Recent studies show that they also have oxygen-binding protein called myoglobin in their muscles, allowing them to store oxygen in muscle tissue when diving. While they do not hold their breath in the conventional sense, some freshwater turtles actually hibernate underwater for as long as six months. This feat involves slowing their metabolic rate and absorbing oxygen from the surrounding water through their skin.