The Deep Sleep Of The Sperm Whale

Whale watching holidays are among the most popular of all nature-focused tours. Witnessing these giant cetaceans in their natural habitat can be a moving and, in some cases, quite profound experience. Well-organised whale watching holidays take participants to some of the best nature hotspots in the world to encounter a wide variety of species.

While humans have always had a fascination for whales, as the largest toothed predator on the planet, the Sperm Whale (Physeter macrocephalus) is one of the most sought-after sightings on whale watching holidays. These big, beautiful marine mammals can be found in deep water in almost all of the world's oceans, with the exception of the high Arctic, so science already knows quite a lot about their ecology. Even so, there is still more to learn.

Sleeping Secrets Uncovered

In Sir David Attenborough's latest documentary series, Blue Planet II, the team collaborated with the Domenica Sperm Whale Project, which has been tracking more than 20 families since 2005. Using innovative suction cap camera technology attached to the animals, called a D-tag, they were able to capture footage that provides an unprecedented insight into their secret world, more than a kilometre beneath the surface of the ocean.

While every minute of the Blue Planet II footage is edge-of-the-seat exciting, perhaps the most memorable is the ethereal sequence of a pod "hanging" in a vertical, tail down formation, in what appears to be a state of suspended animation.

It's believed that the whales snatch these brief periods of vertical sleep to rest and rejuvenate, lasting only about 10-15 minutes at a time. Until fairly recently it was thought that like most other cetaceans they always slept with one eye open, effectively shutting down just one hemisphere of the brain. However, scientific research has now found that these short bouts of slumber that they enter throughout the day are, indeed, total sleep periods. In findings even more fascinating, researchers have observed them exhibiting a similar REM (rapid eye movement) to humans, which is associated with our state of dreaming.

It has been determined that the Sperm Whale spends around 7% of its time drifting (in what's assumed to be their sleep mode). This is in marked difference to other whale species, which drift for up to 41% of their time. This incredibly small amount of time spent slumbering has led researchers to label them as the "least sleep-dependent mammal" on Earth. The fact that they have the largest brain of any animal on the planet makes this fact even more intriguing.  

Art Meets Nature

The work of photographers, naturalists and documentary makers like Sir David Attenborough is not simply important for its entertainment value. In many cases, it results in great scientific gain as well and, in the case of Blue Planet II, takes us into a previously unseen world to discover the secrets of the Earth's most fascinating wildlife.

Author Plate

Marissa Ellis-Snow is a freelance nature writer with a special interest in whale watching. As a passionate lover of marine wildlife, Marissa chooses the expert-led whale watching holidays organised by Naturetrek, which have brought her unforgettable sightings of a wide range of wildlife in some of the most spectacular regions on Earth.