By Marine Biologist Daniele Zanoni
Many people often wonder if dolphins sleep. Most of us know that dolphins are air breathing mammals so they have to get to the surface to breathe. This is, of course, an active process that requires effort and has to be done every few minutes. The breathing frequency depends on the activity of the dolphins. If they are active and swimming quickly, they will have to breathe more often. And since dolphins are not breath-holding champions like sperm whales, they have to breathe anyway every 15 to 30 minutes.
So, the question comes; how do they sleep if they have this important conscious activity to carry out?
And the answer? These amazing animals are capable of sending only half of their brain to sleep. This will influence their behaviour as when they are 'sleeping', they minimize all the body activities to the least required to survive, leaving the animal in a state of semi-consciousness. Which is why they will always swim very close to the surface in order the have the air 'within reach' as they shut down unnecessary internal process, slow down their heart beat and swim very slowly. This happens for an average of six hours per day. People working out at sea or out on boats very often might have seen pods of dolphins behaving this way.
Now you know why. And, who knows, they might even have dreams!
Interested in knowing how marine mammals and sea birds can hold their breath for very long period? Let me know and I will write an article about that as well - email firstname.lastname@example.org