If you’ve ever observed elephant seals lounging on a beach, it might seem like their main activity is sleeping. However, recent scientific findings have shed light on their behavior in the ocean, revealing that they actually sleep very little while at sea. On average, elephant seals only sleep around two hours per day.
These remarkable marine mammals spend the majority of their time submerged in the ocean. For approximately seven months of the year, they remain in the water continuously.
Despite their imposing size, elephant seals must exercise caution in the ocean. Predators such as sharks and orcas pose constant threats near the surface.
Consequently, elephant seals devote much of their time to deep-sea diving in search of sustenance. They are capable of diving to astonishing depths of up to 2,500 feet (750 meters) below the surface and can hold their breath for over an hour. Typically, they dive for about 30 minutes before resurfacing briefly for a couple of minutes to replenish their air supply before submerging again.
Scientists have long been intrigued by how elephant seals manage to sleep while spending prolonged periods at sea, where they engage in nearly continuous diving activity.
Unlike animals like dolphins and sea lions, which employ a unique mechanism where one hemisphere of the brain sleeps while the other remains alert, elephant seals, similar to humans, require both hemispheres of the brain to enter sleep simultaneously.
To unravel the mystery of how elephant seals sleep while navigating the depths of the ocean, scientist Jessica Kendall-Bar devised a groundbreaking solution: a specialized cap capable of recording the seals’ brain activity. This innovative cap also gathered data on the seals’ heart rates, movement patterns, and depth levels. Kendall-Bar and her team outfitted thirteen young female elephant seals with these caps to delve into their slumbering habits.
Similar to humans, elephant seals experience distinct stages during sleep. At times, they maintain control over their bodies, akin to when you’re in a light sleep phase. However, during deep sleep, characterized by vivid dreaming, their bodies undergo temporary paralysis—a protective mechanism to prevent injury during active dream states.
Through their research, the scientists discovered that elephant seals engage in brief episodes of sleep while diving, lasting approximately 10 minutes each. These sleeping sessions mirror the sleep stages observed in humans. Initially, as the seals begin to drift into slumber, they maintain control over their movements, gliding smoothly through the water. However, during deeper sleep phases, they enter a state of uncontrolled descent, akin to a falling leaf, gracefully spiraling in a circular motion.
The seals rouse themselves in time to resurface for air, a vital necessity for their survival. In shallower regions, some elephant seals even awaken while resting on the seabed.
Leveraging the data gathered from the cap-equipped seals, the scientists developed a sophisticated computer program to analyze historical records of elephant seal journeys. This innovative approach provided insights into over 500,000 instances of “sleeping dives.”
Their analysis revealed that elephant seals spend only approximately two hours per day sleeping while in the ocean. Consequently, the quality of rest they attain upon returning to land becomes critically important. On terra firma, these remarkable marine mammals enjoy an average of about 10.8 hours of sleep per day.
The researchers aspire that their findings will contribute to the conservation efforts aimed at safeguarding the habitats where elephant seals rest while on land, recognizing the significance of these spaces for their well-being.