Northern elephant seals sleep in the deep to avoid predators

Northern elephant seals slumber portion drifting hundreds of metres beneath the oversea aboveground - astatine depths wherever their predators bash not usually lurk.

US researchers tracked the animals, signaling their encephalon enactment arsenic the seals swam for thousands of kilometres.

The mammals, which scope depths of up to 2,500ft (760m), slumber for lone 2 hours per time successful what the researchers picture arsenic "nap-like sleeping dives".

The findings are published successful the diary Science.

University of California Santa Cruz researcher Jessica Kendall-Bar and colleagues developed a non-invasive stick-on tag to way and simultaneously show the encephalon enactment of chaotic bluish elephant seals disconnected the seashore of California.

They followed 8 chaotic mammals connected their foraging trips, which lasted astir 7 months and spanned much than 6,200 miles. They recorded the animals' encephalon activity, bosom rate, question and assemblage position.

"We developed a technological 'signature for sleep' by studying their behaviour and physiology for galore years," explained Ritika Mukherji from the University of Oxford, who was progressive successful the study.

It revealed that, astatine depths of much than 984ft, the seals would autumn dormant and descend successful what the scientists picture arsenic "sleep spirals" for astir 20 minutes astatine a time. "They look similar falling leaves," said Ms Mukherji.

Lead researcher Prof Terrie Williams, from UC Santa Cruz, told BBC News: "The happening I find singular is that immoderate mammal would autumn dormant portion drifting hundreds of metres beneath the h2o surface.

"This is not airy slumber but existent paralytic, heavy slumber that would person humans snoring. Remarkably, the seal's encephalon reliably wakes them retired of it earlier moving retired of oxygen.

"Imagine waking up connected the bottommost of a excavation - it sends a shiver down the spine."

The scientists accidental their survey has drawn "nap maps" for seals - suggesting that sleeping areas whitethorn beryllium arsenic important arsenic progressive hunting areas for these animals.

Ms Mukherji explained: "It shows america what their satellite looks similar and helps america to recognize what they're doing and erstwhile they're doing it, truthful we tin recognize however to debar getting successful their way."