How Do Whales Sleep Without Drowning?

Scientists understand very little about how whales sleep. An observation by scientists observing sperm whales off the coast of Northern Chile has shed some light on the subject.

To ponder the question of how whales sleep, one must first understand how whales breathe. Whales breathe oxygen from the air and must surface to breathe. Humans do not need to consciously think about breathing; whales do. Whales hold their breath when underwater and inhale and exhale through nostrils located on top of their head when they surface. Whales must surface periodically to breathe and stay alive. It is not much different than a human swimming. Humans hold their breath when underwater and surface to breathe. Can you imagine sleeping underwater? While asleep, you would have to remain conscious of holding your breath underwater and remain conscious of your need to surface when your oxygen supply ran out. This is what whales do.

Some scientists have theorized that only half of a whales' brain sleeps at a time, leaving the awake half of the brain to respond to air requirements and their surroundings. The observations by the scientists in Northern Chili who observed the whales sleeping in the wild suggest that both halves of a whales' brain sleep simultaneously. The scientists observed a group of whales sleeping just below the surface of the water in a vertical position with their heads pointing toward the surface. The whales surfaced to breathe and resumed their vertical position just under the water. Some of the whales had both of their eyes shut and did not respond to boats around them. One whale did not respond until a boat accidentally brushed against him. The lack of response to nearby surroundings suggests that the whole brain of the whales were concurrently sleeping. The fact that one whale awoke when brushed by a boat strengthens the suggestion of whole brain sleep. The whale was unresponsive and seemingly unaware of the boat until it touched and awoke him.

Scientists don't fully understand how whales sleep without drowning. It is obvious that a whales' brain and body functions differently than a humans', giving them the ability to sleep underwater without drowning. Scientists have had only limited opportunities to observe whales sleeping in the wild. As a result of limited observations of whales in the wild, scientists theorize that whales only sleep for short periods at a time.

Resources

• The Telegraph
• Fisheries and Oceans Canada