Since Dolphins are like human being in so many ways. For example, dolphins have a special respiratory system just like humans. The only difference is that dolphins are able to stay underwater for a long time without breathing oxygen. But how do dolphins manage to sleep without drowning?
Generally, dolphins sleep with only one brain hemisphere in slow-wave sleep at a time, thus maintaining enough consciousness to breathe and to watch for possible predators1
and other threats. Earlier sleep stages can occur simultaneously2
in both hemispheres. In captivity3
, dolphins seemingly enter a fully4
asleep state where both eyes are closed and there is no response to mild external stimuli5
. In this case, respiration6
is automatic; a tail kick reflex keeps the blowhole above the water if necessary. Anesthetized dolphins initially7
show a tail kick reflex. Though a similar state has been observed with wild sperm8
whales, it is not known if dolphins in the wild reach this state. The Indus river dolphin has a sleep method that is different from that of other dolphin species. Living in water with strong currents and potentially dangerous floating debris9
, it must swim continuously to avoid injury. As a result, this species sleeps in very short bursts which last between 4 and 60 seconds.