Danish Nobel-laureate August Krough once said in what is now known as the Krough Principle, "for [many] problems there will be some animal of choice, on which it can be most conveniently studied." This means that if you are interested in studying a certain trait, such as a nose’s ability to smell, the organism to study it on should have a very exaggerated form of that trait. An example of this in neurobiology is the squid and its giant axon. These cephalopods developed a giant axon as a way to relay sensory information through their elongated mantle to their brain as instantaneously as possible. For this reason, squid are often the animal model used in basic research on neurons with implications for human health.
To understand the sense of smell (olfaction), it seems reasonable that studying the animal with the world’s largest nose would be a good place to start. So which organism has the largest nose in the animal kingdom? While Cyrano de Bergerac or an elephant would be good guesses, by most traditional measures, the Sperm Whale (Physeter macrocephalus) takes the cake.
The Sperm Whale is the largest toothed predator to ever live, growing to a maximum length of 20 meters (65 feet) and weight of 60 tons (120,000 pounds)! Despite these colossal dimensions, their most striking physical feature is their huge, blocky head. Heck, their species’ name, macrocephalus, means “large head.” This unusual noggin is mostly nose and neighboring structures. The Sperm Whale’s nose accounts for roughly a third of the animal’s total length and weight. This led Danish physiologist Bertel Møhl to quip that a Sperm Whale is basically just a nose with an outboard motor.
With such a tremendous nose, the Sperm Whale must possess an amazing sense of smell, right? Wrong. All odontocetes (the toothed whales; e.g., dolphins, Orcas, beaked whales, etc.) including Sperm Whales have no olfactory bulb, the region of the vertebrate brain essential for transmitting and deciphering olfactory information. In other words, they are believed to have no sense of smell whatsoever! So what is this massive nose used for?
In 1985 Sperm Whales were given full international protection from hunting, but for the two centuries prior, whalers killed over one million Sperm Whales, reducing their global population by nearly 70%. What made Sperm Whales so highly sought after was not their meat or blubber, but their spermaceti. Approximately 5000 liters (over 1000 gallons) of this waxy substance can be found in an adult male Sperm Whale’s head, and once processed it can be used for lubrication, leatherworking, lipstick, and lantern fuel. Spermaceti in liquid form closely resembles… well, male ejaculate of course. It’s how the Sperm Whale got its common name.
Like other toothed whales, the Sperm Whale finds its prey by echolocation, sending out an intense beam of high-frequency sound, listening to the returning echoes to locate prey at depths of 200-2,000 meters. However, the spermaceti organ is unique to Sperm Whales, but why? The reason is because spermaceti has an incredible resonating capability.
Here’s how it works: a Sperm Whale produces an echolocation click near its blowhole; counterintuitively, the sound travels backwards towards the base of the head, through the spermaceti organ. At the base of the head, the sound is reflected off an airsac and focused out through the front of the whale’s head.
This circuitous route helps make the sound as loud and directionally focused as possible. Measured at 230dB underwater – equivalent to 170dB on land (as loud as a gunshot three feet away) – the Sperm Whale’s echolocation click is the loudest biologically produced sound on earth and it wouldn’t be possible without their unique spermaceti organ. So there you have it, the largest nose in the animal kingdom is actually the world’s most powerful biological resonating chamber.
(Side note: how does the giant squid, the Sperm Whale’s favorite prey, stand any chance against these whales, capable of detecting squid over 500 meters away in nearly complete darkness? Read my post from last October to find out.)
The Sperm Whale is an auditory wonder, fine-tuned over millions of years of evolution. To protect these amazing creatures into perpetuity, society needs to consider how we are impacting Sperm Whales today. Anthropogenic noise pollution from shipping traffic, naval operations, and oil exploration negatively affects a myriad of oceanic life including marine fish, baleen whales, and the aforementioned cephalopods. However, the consequences may be gravest for the toothed whales. For example, scientists have evidence to suggest that beaked whales quickly dive to and from great depths to evade loud sounds, giving them decompression sickness – known by its more familiar name, the bends – which may lead to stranding. It has also been shown that Sperm whales avoid anthropogenic noise, which has been implicated in their stranding.
It is time to use our knowledge of sensory biology for good, developing mitigation strategies that protect toothed whales from pervasive noise pollution. If we do so, future generations can continue to marvel at the world’s most impressive noses that cannot smell a thing.
Matthew Savoca holds a PhD in Ecology from the University of California, Davis. His research interests include sensory behavioral ecology, marine conservation biology, and seabird ecology.