THAR SHE BLOWS! SPERM AHOY!

Next month, we return to Dominica to spend two weeks snorkelling and free diving with the  largest predator in the ocean, the magnificent Sperm whale. Of all the cool encounters I have had in 15 years of marine adventures, being a few metres away from the giant eye of these super-intelligent deep-diving hunters is somewhere in the top five. 

Over 20 different Sperm whale families have been identified in the waters around Dominica, and there are about 10 that are seen regularly. Based on researchers’ images, It is known that they have been using these waters since at least 1984, but likely much longer based on their life history. Sperm whales can live to be older than 70 years, meaning they meet a lot of other whales over their lifetime. It would appear that families have preferences with each other, and these social preferences endure across decades, suggesting that individuals can remember each other despite long separations.
 
Researchers think this social recognition is mediated by distinct dialects of Morse code called ‘codas’. Each family has a slightly different coda repertoire, but also share coda types with the other units in the Caribbean. Shared repertoires delineate socially segregated ‘vocal clans’ – collections of units that share a similar coda dialect. Units which share the same dialect associate and spend time together and units that have different repertoires never gather together.
 
 In the Caribbean, the '1+1+3' coda type, which sounds like 'Click-pause-Click-pause-Click-Click-Click', is unique to the region. It has been used for at least the last three decades, and is made the same way by all the whales use it, like a marker of Caribbean nationality.

For more info on our Dominica Sperm Whale trips, go here. ​

Evolution
Fifty-five million years ago, a group of hoofed mammals began a slow move from shore to sea, in time evolving a set of extraordinary features to thrive in their new environment.
 
Today’s whales share many anatomical traits with other mammals, but the unique adaptations of species such as Physeter macrocephalus, the Sperm whale, illustrate how organisms can transform over time as they carve out their place on the planet.
 
The sperm whale's sleek shape is well-suited for deep diving, this species' specialty. Sperm whales can dive over 6,500 feet, remaining under water for more than an hour. Sperm whales dive deep into the ocean for prey like giant squid.
 

Unlike fish, which swim by moving their tails side to side, whales and dolphins move their flukes up and down. Sperm whale flukes are the largest, relative to body size, of any whale. The sperm whale's flippers, or pectoral fins, help the animal manoeuvre through water. They also share bone structure with the human arm and hand.

​In fact, the bones of cetacean flippers are the same kinds of bones as in the human arm, with an upper arm bone, two forearm bones, and hand, wrist, and finger bones. In whales, fingers are elongated and may have additional bones. The joint between upper arm and forearm is immobile, creating an effective paddle.
 
Echolocation
Among sperm whales' (and other toothed whales') most amazing adaptations is echolocation, the use of sound to locate objects based on their echoes−and a way of navigating the world that is also used by some land mammals, including bats. The whales use this ability to, among other things, hunt successfully for deepwater prey, such as giant squid, their meal of choice.
 
To create sound, the whale pushes air through one of its nasal passages to a pair of flaps that vibrate to create sound. The sound passes through the spermaceti organ (in blue, top of the skull), bounces off an air sac, and is redirected to the whale's "melon" organ (in yellow). Called "junk" by whalers, this organ contains fatty tissue that transmits sound, focusing the pulses in the process and allowing sperm whales to direct, or aim, sound waves.

The  sperm whale's head is actually an oversized nose, which in mature males can make up a third of the animal's body. Sperm whales use their uniquely shaped nose to generate sound. 
 
At the crux of the whale's jaw, the lozenge-shaped yellow portion (shown above, right) is the "acoustic fat pad." As echoes bounce back toward the sperm whale, they are received by this deposit of fat in the back of the whale's long, thin jaw. The sound is then transmitted through the ear bones. 

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This is what happens when all you eat is giant squid. 

For more info on our Dominica Sperm Whale trips, go here. 

Infographics courtesy of © AMNH/5W
Photo taken under permit from Dominica Department of FIsheries