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The Migration Trail: Any Shut-eye Along the Way?

Do Whales Sleep?
Photo: Keith Jones

 
Taking a snooze near the surface?
Photo: Jane Duden

Wondering About Rest. . .
Gray whales travel 24 hours a day. Could they possibly make their 10,000-mile annual migration without any rest or sleep?

Gray whales are voluntary breathers. This means they have to think each time they take a breath. Humans don't have to do this. We basically go unconscious while we sleep and breathe automatically. How do whales sleep if they must be conscious to breathe?

For many years, scientists were unsure about these questions. They had long observed whales lying motionless on the surface in an activity called logging. Whales "log" for 20 to 30 minutes at a time, but no one knew what was actually happening. Whales were resting during these periods, but were they sleeping? If so, do they sleep like we do?


Research: Looking for Answers
Dolphin Sleep: The First Breakthrough
For many years, people who worked with dolphins thought these marine mammals could shut down half their brain and rest it. The other half would stay active. This sounded far-fetched, and scientists were skeptical about the idea. But then a Russian scientist put this idea to the test. He placed electrodes on the heads of bottlenose dolphins and recorded their brain waves over time. His results showed that these dolphins did put half their brain to rest at a time, while the other half remained active! Were whales doing the same thing, allowing them to "sleep" for short periods each day?

Gray Whale Observations in a Sea World Pool
A team of scientists, still searching for clues on gray whale sleep, studied a rescued gray whale in a pool at Sea World. For nine days, they made continuous video-recordings and observations. They collected data on the whale's behaviors. Here's what they found:

  • The gray whale rested in two ways: (1) by hanging just below the surface with its blowhole above water and (2) by lying on the bottom of the pool.
  • In both cases, the whale's breathing slowed. Its fins and tail moved slowly until it was fully resting. Then the whale only moved to take breaths of air.
  • When the whale rested on the bottom of the pool, it rose to the surface every few minutes and breathed.
  • At different times, the whale slept with both eyes open, both eyes shut, and just one eye open (indicating that only half its brain was active).
  • The whale was more likely to be active during the day and resting or sleeping at night.
  • During sleep, the whale's body sometimes jerked and twitched. In humans and other mammals, these movements indicate a deeper state of sleep (and dreaming).

More Questions!
Each study adds a little more to our understanding of whale sleep. But plenty of questions remain. Here are a few:
  • Would gray whales behave the same way in their natural environment?
  • Do migrating whales rest or sleep in the same way as whales that are on feeding and breeding grounds?
  • Could gray whales safely rest on the bottom in shallow waters?
  • Do gray whale calves have different sleep habits than adults?
  • Do gray whales dream?

Journal or Discussion
  • What questions do YOU have about gray whales and sleep? How would you try to go about finding answers?



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