The largest predatory animal that ever lived on Earth

Published by Simon Mustoe

“Another thing that got forgotten was the fact that against all probability a sperm whale had suddenly been called into existence several miles above the surface of an alien planet. And since this is not a naturally tenable position for a whale, this poor innocent creature had very little time to come to terms with its identity as a whale before it then had to come to terms with not being a whale any more.” 

Douglas Adams, The Hitchhiker’s Guide to the Galaxy


Sperm Whales are as alien to our environment as we are to their deep ocean home. Here’s an animal that routinely travels to places less well mapped than the surface of the moon, where water pressure is crushing and sunlight never seeps.   

Next week a group of Wildiaries travellers are heading to Raja Ampat to search for this, the largest predatory animal that ever lived on Earth! Surely dinosaurs were bigger, I hear you say. Nope, the mighty Sperm Whale has always held the record. 

The name comes from ‘spermaceti’, liquid oil in the head that hardens when cooled. The oil’s full function is disputed but seems to help with buoyancy as well as a superbly sophisticated echolocation system.

There are so many things about Sperm Whales that capture imagination. 

They are supremely adapted creatures with a long history in folklore and whose oil lit the lamps of London for decades. Devastating whaling almost certainly contributed to the industrial revolution. 

Controversially, Sperm Whale oil is also the lubricant of choice for space exploration because it doesn’t decay. It’s in the Hubble telescope and Mars Rover vehicles. It’s even used in nuclear weapons. 

The first time I saw a Sperm Whale it was in the north Atlantic between Scotland and Iceland. In these near-polar waters, you tend to mostly find solitary males. Nearer the equator live inter-generational groups of females and their offspring. Groups can number many dozens of animals. 

First sight is usually at a distance: a low-angled blow emanating from a log-shaped dark patch in the water. The whales rest motionless as they recuperate from epic 45 minute dives. Sperm Whales spend most of their lives at depth.

Sperm Whales use echolocation in the same way as bats. Both have very excellent eye sight but what’s the use in the dark? After diving Sperm Whales turn to sonic vision to find prey but that means producing your own sound, to build a picture of their world from the noises that bounce off objects in the gloom.

Because you can hear Sperm Whales underwater, sometimes several kilometres away, you can track them. Years ago I was employed to do the first acoustic tracking of Sperm Whales for the oil industry in Bass Strait, off Victoria, Australia - a method known as ‘passive acoustic monitoring’. Just north of Flinders Island and south of Cape Conran (Vic), there is a huge canyon. Heavy salt-laden ocean flows like a waterfall over the ridges and Sperm Whales abound. There are rich-pickings to be had in such dynamic seas. 

In Raja Ampat, the ocean floor plumbs to thousands of metre deep just offshore, also ideal Sperm Whale habitat. We’ll be using a hydrophone set inside a parabolic reflector, which allows us to work out the direction their sounds are coming from.  

For all their apparent ferocity, they feed on surprisingly small, gelatinous squid, hoovering up a few hundred a night, mostly about 30cm long. Occasionally they tackle Glass Squid, Giant Squid and even Collossal Squid (as larger squid are discovered, the superlatives get more extreme). Chitinous squid beaks found undigested in the stomachs of dead Sperm Whales have been used to estimate the size of their tentacled prey.  

What’s even more remarkable is no-one has ever seen a Sperm Whale feeding. How does an animal with a skull the size of a bus manage to catch foot-long gelatinous prey with a long-lever jaw and mouth slung below its monstrous head? And what are the purpose of those rows of enormous teeth?  

When a Sperm Whale dives, it does so silently. It arches its back, lifts its tail and descends vertically into the abyss. Scientists have tried attaching cameras with suction-cups to their flanks. Curious about the objects, whales have stopped, inspected the cameras and knocked them off before continuing on their journey.

What can we surmise about an animal with a brain six times bigger than ours? Perhaps there are things Sperm Whales would prefer we didn’t know.       

Within a few moments, as the shafts of sunlight start to disappear, Sperm Whales start echolocating. One half of their nasal cavity is sealed off to produce the noise. At about 200dB, this explosive ‘click’ is one of the loudest natural sounds in the ocean. 

The back of the skull is shaped like an enormous convex mirror so sound travelling towards the tail is gathered, focused and bounced forward - in the same way as light can be focused using a magnifying glass - and intensifies as it travels through a series of fatty lenses full of spermaceti oil, until it forms a narrow beam that’s projected out into the ocean. 

So the click is actually a double click, the first being the source and the second being the beam that is ejected from the jaw milliseconds later. Scientists can even measure the length of Sperm Whales and the composition of whole groups of whales, by listening to the interval between these clicks, which corresponds to twice the distance between the nasal cavity and skull.        

Echoes are then received along the dense jawbone and processed by that enormous brain. We can’t begin to imagine how the world ‘looks’ to an animal who sees with sound but it’s clearly high enough resolution to catch small, fast-moving jelly-like animals. When squid are detected, Sperm Whales even produce a buzz, rather like bats - as they home in on prey, the clicks get more rapid, enabling them to fine-tune their detection and zero in on their meal.

Years ago I was on a ship bearing down at only 4 knots towards a surfaced Sperm Whale. The vessel had to steer away to avoid collision and the crew were perplexed. Why would such an animal not try to avoid a collision?

The answer now seems so obvious and illustrates how narrowly we perceive the world around us. 

The largest predator that ever lived on Earth had nothing to fear for millions of years. It adapted to live in a place alien to our own understanding of existence, where all its efforts were focused on feeding and surviving in the most extreme environment on the planet. Ships only appeared ‘on the radar’, a hundred or so years back. A Sperm Whale has as much chance of noticing a 20,000 tonne ship coming up behind it, as we would notice a silent killer bearing down on us with only the light of a a torch shone on the back of our head.        

The fact they’re perfectly adapted to a world we don’t understand, makes Sperm Whales one of my favourite animals and surely one of the world’s most baffling and incredible creatures. 

Wildiaries • February 2017