Since Tuesday (15 March 2016), Singapore’s very own sperm whale (Physeter macrocephalus) specimen (aka Jubi Lee) has been on display at the Lee Kong Chian Natural History Museum. Jubi is the first known record of a sperm whale in Singapore waters, and was discovered last year when her body was found floating off Jurong Island. At 10.6m in length, Jubi is slightly smaller than an average female adult. Sperm whales are the largest toothed whale, and males are known to grow to around twice that size!
One thing that fascinates me about sperm whales (other than its sheer size) is the distinctive blockish shape of its huge head, especially when you compare it with the shape of its skull. What evolutionary advantage does this odd looking head give to sperm whales?
Looking at the cross section above, you can see that quite a large portion of a sperm whale’s head is made up of the spermaceti organ and junk. Whalers used to believe that the spermaceti organ produces sperm, hence the name. We now know that this organ actually produces and stores large amounts of spermaceti (an oily fluid consisting of triglycerides and wax esters). There are two main theories as to the function of the spermaceti organ. The first theory is based on the melting point of spermaceti. When sperm whales dive into the depths of the oceans, it is hypothesised that the colder water comes in contact with the organ, reducing blood flow, thus lowering the temperature of the spermaceti to below 30°C. This causes it to solidify and increase in density, allowing the whale to sink more efficiently. The reverse happens when the whale starts to surface.
The second theory is that the spermaceti organ and the “junk” organ below it help in echolocation. It conducts sound twice as well as the oil found in the melon of other cetaceans (such as dolphins), potentially making echolocation more effective.
Given that sperm whales are pelagic creatures and spend most of their time in deep oceans away from coastlines, it may take a while before we can confirm if either (or both!) theories are correct. Hope you’ve learnt something new, and didn’t get over-whale-med!