Scientists have documented the brain activity of an unrestrained, untamed marine mammal, exposing the sleeping habits of elephant seals throughout their prolonged ocean stay for the first time.
As per a new study, titled, "Brain Activity of Diving Seals Reveals Short Sleep Cycles at Depth" published in Science, elephant seals sleep for only 2 hours per day when on months-long foraging trips or an average of 10 minutes at a time during sleep. Although, they spend 10 hours a day sleeping on the beach during the breeding season.
Sleep Habits of Elephant Seals During Foraging Months
According to a press release via EurkeAlert! a team of researchers led by Jessica Kendall-Bar, a former UC Santa Cruz graduate student, conducted a study on elephant seals to answer one of the central questions about their behavior: when do they sleep?
The research was carried out in collaboration with Daniel Costa and Terrie Williams, both professors of ecology and evolutionary biology at UCSC. Costa's lab has been studying elephant seals for over 25 years using increasingly sophisticated tags to track their movements and diving behavior during their foraging migrations in the North Pacific Ocean that can last up to eight months.
The research showed that elephant seals are constantly diving and possibly sleeping during their "drift dives," when they stop swimming and slowly sink. The team's findings indicate that elephant seals sleep very little compared to other mammals during their months at sea, possibly even less than African elephants, who currently hold the record for the least sleep among all mammals, sleeping only two hours per day based on their movement patterns.
Elephant seals are unique in that they switch between getting over 10 hours of sleep when they're on land and only two hours or less when they're at sea. However, they are at their most vulnerable to predators such as sharks and killer whales when they are at the surface in the open ocean.
Therefore, they spend only a minute or two breathing at the surface between dives. As they can hold their breath for a long time, they can safely go into a deep slumber on these dives deep below the surface. Kendall-Bar said this behavior explains why elephant seals have the ability to sleep so little and still function normally during their months at sea.
Measuring Elephant Seals' Sleep Spiral Under the Ocean
In a similar article from SciTech Daily, the news outlet reported that Kendall-Bar developed a new system that uses EEG sensors, a neoprene head cap, and a data logger to monitor the brain activity of elephant seals during their normal diving behavior in the wild. Researchers were able to track the seals' movements and corresponding brain activity, even in deep sleep.
The seals also carried time-depth recorders and accelerometers to provide further data. The research showed that the seals enter slow-wave sleep before transitioning into rapid-eye-movement (REM) sleep, where they turn upside down and drift downwards in a "sleep spiral" of up to 1,235 feet (377 meters) deep in the ocean. This information could be useful for conservation efforts by identifying important resting areas.
The new system was first deployed on elephant seals housed temporarily in marine mammal facilities at the University of California, Santa Cruz's Long Marine Laboratory. They then deployed it on animals in the elephant seal colony at Año Nuevo Reserve, where researchers could observe the animals on the beach.
The research provided data on brain activity and dive behavior from 13 juvenile female elephant seals, which was used to develop a highly accurate algorithm for identifying periods of sleep based on dive data alone. It enabled researchers to estimate sleep quotas for 334 adult seals using dive data recorded over several months during their foraging trips.
RELATED ARTICLE: Female Elephant Seal Spends 80% of Their Day Foraging Small Fish in Deep Seas
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