Our traditional boat enjoyed some wonderful sightings today with a range of toothed whale species decorating the deep blue surface of the Atlantic including Bottlenose dolphins (Tursiops truncatus), Short-beaked common dolphins (Delphinus delphis) and Striped dolphins (Stenella coeruleoalba). Of course I made an effort to share as much information as possible with our lovely guests and this is often coupled with questions from my listeners. I simply love questions from our guests since it also prompts to get my nose back into the books and do some digging. The beautiful thing about the natural world is that there is always more to learn and understand and this is especially true for cetaceans.
One enthusiastic guest asked how dolphins regulate pressure in their ears when they dive. Well first of all, a dolphins ear is differently structured to that of a humans. Like in humans it is located just behind the eyes but unlike in humans it is very small and does not directly receive sounds from the marine environment. Instead sound propagates through their throat where it eventually reaches the inner ear after passing through fat-filled cavities, a hearing mechanism perfectly adapted to their sonar use.
A study conducted on Striped dolphins in 2007 also shed some light on how this organ helps the animal regulate pressure and prevent barotrauma during diving. The scientists anatomical and histological study on the six stranded animals highlights the importance of the corpus cavernosum, a structure that fills the cavities of the middle ear in dolphins. It consists of erectile tissue that allows the structure to regulate the air-filled cavities of the middle ear, a potential obstacle for these mammals during deeper dives. The researchers suggest possible functional variations in the structure during diving may be the solution to this problem, with it being turgid in shallow waters and narrow in deeper waters.
This possible adaptation remains a theory and may not be applied to the ears all dolphins but certainly shows the important role of this organ in cetaceans. Another lesson learned after an encounter with these wonderful creatures.
By Paula Thake
Sightings of the day
10:00 Bottlenose dolphins, Short-beaked common dolphins, Striped dolphins