The age of a tree can be determined by studying its trunk. Likewise, the age of certain whales can be determined by examining their ears.
The ear wax of Fin Whales and some other species of baleen whales is different from the kind that clogs our own ears. The whale variety forms a hard plug that seems to improve hearing rather than impair it. Also, the ear wax of these whales thickens in distinct layers each year -- two layers annually for the Fin Whale, while the Humpback Whale appears to add four layers of ear wax per year.
Once a person knows the appropriate rate of wax buildup for a given species, it's relatively easy to calculate the whale's age. Unfortunately, the whale must be dead in order for its ear plug to be extracted and studied. The surest method for determining the age of a living whale is to check its ID.
Click here to learn more about the endangered Fin Whale.