Need more sleep? Tell that to an elephant seal
WASHINGTON — Sleep is a precious commodity for people and across the animal kingdom, indispensable even as its biological purpose remains somewhat mysterious. We spend about a third of our lives asleep. But some animals get a lot less slumber — with certain species like the northern elephant seal taking sleeplessness to an extreme.
Researchers in a new study described the unusual sleep habits of this species, finding that during Pacific Ocean foraging journeys that can last seven months these bulky marine mammals sleep just two hours a day — cobbled together from naps of about 10 minutes each as they dive deep to avoid predators. The only other mammal known to get so little sleep is the African elephant.
The seals’ sleep duration during these ocean voyages differed significantly from the 10 hours a day they spend sleeping on the beach during the breeding season at places like California’s Año Nuevo beach.
The researchers placed on the heads of the seals a noninvasive waterproof synthetic rubber cap with sensors to monitor sleep signals generated by the brain, heart rate, location, and depth. The researchers focused on female seals because they engage in long open-ocean journeys while males feed in coastal waters.
The study documented unorthodox sleep behavior.
During dives lasting about 30 minutes, the seals went into a deep sleep stage called slow-wave sleep while maintaining a controlled downward trajectory. When they then experienced rapid-eye-movement (REM) sleep, a stage causing sleep paralysis, the seals drifted into a corkscrew “sleep spiral,” turning upside down and sometimes ending up motionless on the seafloor.
“Then, at the deepest point of their sleeping dive — up to 377 meters deep (1,237 feet) — they wake up and swim back to the surface,” said Jessie Kendall-Bar, a postdoctoral fellow at the University of California San Diego’s Scripps Institution of Oceanography and lead author of the study published this week in the journal Science.