In the Indian Ocean, a captivating sight unfolds as over 30 adult sperm whales are discovered sleeping at a depth of 15 meters. All females, their calves remain at the surface while the parents rest. This intriguing behavior was captured by French photographer and filmmaker Stephane Granzotto while diving in the Mediterranean. He was documenting sperm whales for his photo book titled “Cachalots.”
The whales, almost the size of school buses, stand vertically in the water, seemingly motionless and arranged in pods of five or six. According to Granzotto, they had been napping for an hour. A 2008 study published in the journal Current Biology was the first to conclusively document this vertical sleeping position. Using data-collecting tags attached to 59 sperm whales, researchers from the University of St. Andrews and the University of Tokyo measured the animals’ periods of inactivity.
The whales were found to spend seven percent of their day in these vertical sleeping positions near the surface, where they nap for 10 to 15 minutes. Researchers suggested at the time that they might be one of the world’s least sleep-dependent animals. Whales in captivity have been found to use only half their brain while sleeping, a behavior scientists think could help them avoid predators, maintain social contact, control breathing, or continue swimming.
The study also noted observations from a video shot in northern Chile that showed whales did not wake from their surface naps until a ship approaching with its engines off unintentionally bumped into them. This suggests that whales in the wild might enter a full sleep, unlike their captive counterparts.
The images above are property of National Geographic.
