Free the Ocean Blog

Elephant seals sleep while they dive!

Ever wondered if you could sleep and work simultaneously? Northern elephant seals are way ahead of us on this, as they’ve mastered the skill of sleeping and diving together, while also keeping a keen eye out for predators.

These champs can travel thousands of miles during their seven-to-eight-month-long foraging trips in the North Pacific Ocean. This naturally led scientists to ask – where and how do these marine mammals get their snooze on amidst their aquatic adventures?

Photo Credit: Jessica Kendall-Bar

Unraveling the Sleep Spiral

A recent study took a deep dive into the sleep patterns of these marine mammals. The seals were fitted with cap-like devices used in sleep clinics to study human sleep disorders. The results? Astonishing! Elephant seals take short naps while they dive deep into the ocean, holding their breath all the while.

As they enter the stage of REM (Rapid Eye Movement) sleep, they lose control over their body posture and spiral downwards, a phenomenon researchers have adorably named the ‘sleep spiral.’

Sleep Data Dive

This groundbreaking study was the first to record the brain activity of free-ranging wild marine mammals. It captured data from 104 sleep dives and presented a compelling image of marine mammal sleep patterns.

Imagine waking up from a deep slumber at the bottom of a pool and then having to swim up quickly for air. Well, elephant seals are doing this daily. In these half-hour dives, the seals take 10-minute naps, managing to catch about two hours of sleep per day.

Interestingly, the elephant seal might soon be rivaling the African elephant, which currently holds the record for the mammal getting the least amount of sleep.

Innovative Research

The researchers used a unique, waterproof system that could withstand the pressures of the deep ocean, similar to an EEG. These special sleep-monitoring devices, fitted on neoprene headcaps, captured the sleep signals generated by the seals’ brains. The data was then stored in a logger which also recorded the animal’s position and behavior. This fascinating technique enabled the recreation of the sleeping dives, adding another layer to our understanding of marine mammal behavior.

The Big Nap Beneath the Waves

Elephant seals navigate challenging predator-laden environments by spending about one to two minutes at the ocean’s surface for air. They then go on 30-minute deep dives, sneaking in a nap in the safe depths.

These snoozing seals spiral downwards, looking “like a falling leaf,” all while in a stage of deep sleep called slow-wave sleep. Elephant seals have proven themselves not only as extraordinary divers but also as adept sleep divers!

Photo Credit: Jessica Kendall-Bar

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