Sleeping beauty is alive and well

The well fed organism welcomes rest! Seals can sleep partly submerged in water, their noses above water for breathing without waking up fully. A special way of their sleeping is called unihemispheric, slow-wave sleep. One half of their brains are awake in this state, for keeping an eye on their surroundings. This allows them to rest while still alert for danger. Baboons or people would appoint a sentinel for the rest of the troop to sleep normally but to each his own.

Living in water, the sleep on the rocks may last only for so long one might think as a non-seal, before aches and pains will trigger a move or return to the water. Sunning and resting the swimming muscles should, however, also count for something in adopting these daily or less regular options. As is the case for many mammals, seals sleep for short periods, unlike humans but excluding millions of human babies.

The amount of sleep a seal needs depends on many factors, such as predator prevalence or whether there are pups to care for. As in the case of many species that sleep for resting bodies and recovering energy, it is believed that seals also remain healthy, retain mental alertness and maintain their immune systems from sleep. Climate change and losing their favourite sleeping places are threats to their wellness.

Deeper seal sleep occurs on land, while a less restful sleep form happens in water. REM sleep marked by rapid eye movements is key for seal brain health, just like for people and many other species. Brain rest is vital for cognitive functioning. Seals can reach this sleep stage while floating on the surface of the water.

These sleepers may be Cape fur seals (https://animals.mom.com; https://www.wildlifefaq.com).