By Leah Trigg
Sperm whales are the largest of the toothed whales and can grow up to 18 m in length. Their most prominent feature is their head, which makes up approximately one third of their total size. They live in stable mother-led families and are thought to live up to seventy years. They are famous in the whale world for being particularly deep divers – venturing into the depths for their favourite food, the Giant Squid.
Recently, sperm whales have been raised from the deep and brought to the forefront of human consciousness by the sad sight of these ocean giants ailing on the beaches of the North Sea. Our dismay and inability to understand what had brought these magnificent animals to an untimely end serves to highlight how little we still know about life in the ocean. Observing the surface of the ocean leads to only rudimentary insights into how its inhabitants live. We are often left to wonder about what lies beneath the waves. Or are we…?
If you have been reading the blog you probably already know that, among many other oceanographic pursuits, we have spent the last three weeks using underwater sound to understand the number and distribution of sperm whales in the North Atlantic. We have been towing a hydrophone, which gives us a rare window into the ocean deep and has allowed us to record some amazing examples of sperm whale clicks. Take a listen for yourself here. The sperm whale makes regular clicks that sound very much like the blows of a hammer. If you listen carefully you can also hear the regular slap of the ship’s propeller.
The underwater world is one of sound. Very little light penetrates into the depths of the ocean making it difficult for the organisms that live there to rely on sight. Sound, however, propagates very efficiently in seawater and sperm whales have mastered the use of sound for vital life processes such as communication, navigation and prey detection. We can use the sounds produced by sperm whales to count the number of individual whales, pin point their location relative to the ship and even estimate their size.
Initial observations suggest that we have recorded the most sperm whale clicks between the shelf break and a seamount called Anton Dohrn. It will be interesting to put together our final data and discover if this really is the case. Not surprisingly, this observation gives rise to important questions for the future such as, what is it that makes this area particularly attractive to sperm whales.
So while the work continues to unravel the mysteries that the sperm whale and its fellow oceanic inhabitants hold close, next time you find yourself gazing out to sea, try to imagine the bustling oceanic metropolis that is out of sight and just what it might sound like…