Photographs have appeared on several occasions showing gatherings of sperm whales that apparently do not move and are arranged vertically in the water.
Why are these sperm whales upright?
These mammals, which are about the size of a bus, almost always appear to be “standing upright” and in groups of five or six.
French photographer and director Stephane Granzotto has portrayed this behavior during a dive in the Mediterranean, where he was documenting sperm whales for his photographic book on these creatures entitled Cachalots.
A study published in 2008 in the journal Current Biology was the first to conclusively document the vertical position that whales adopt to sleep.
Previously, some cetaceans had been observed sleeping in captivity by tracking their eye movements. However, much less had always been known about how whales slept in the wild. Using data collection devices attached by suction cups to 59 sperm whales, researchers from the University of St. Andrews and the University of Tokyo measured the animals’ periods of inactivity.
It was found that the whales spent seven percent of their day in these vertical positions near the surface of the water, where they slept for 10 to 15 minutes. The researchers then suggested that they may be among the least sleep-dependent animals in the world.
Captive whales have also been found to use only half of their brains when sleeping, a behavior that scientists believe helps them avoid predators, maintain social contact, control breathing or keep swimming.
The study also pointed to observations obtained from a video recorded off northern Chile that showed the whales did not wake up from their nap until an approaching boat with its engine off accidentally collided with them. This suggests that the whales in the wild may be fast asleep, unlike their captive relatives.