28.06.2019 – Scanner
We started the day with a lovely snorkelling tour where our excited guests enjoyed the chance of meeting an interactive group of Atlantic Spotted dolphins (Stenella frontalis) in the water. Like all other toothed whales, this species possesses a fatty organ in their foreheads commonly known as the melon in dolphins that receives the sound waves created in the nasal passages near the blowhole and modifies them according to use. Amongst other things, the generated biosonar emitted from the animals forehead is used as a scanner of sorts by zapping sound waves at objects in the water and receiving the waves reflected off the object in fatty tissue in the lower jaw. This information is then transmitted to the inner ear so, essentially, it is acoustic.
This acoustic scanning of ones surroundings makes perfect sense in an environment where sound travels up to 4 times faster than in air and where visual signals are close to useless beyond a specific depth and time of day. When approaching us in the water, dolphins do so beak-first and often adopt a nodding movement as they scan us from head to toe. This approach is often accompanied by a creaking sound that resembles that of an old door being opened and, if the animal is interested, is closely followed by an initiation of eye contact. So before getting a visual, dolphins scan us up; an understandable safety precaution.
Apart from biosonar, the melon is known to produce a concoction of sounds many of which are used for communication amongst the animals. Along with a series of other sounds, that combined form a sort of “language” which we are eons away from deciphering, dolphins identify themselves using so-called signature whistles. Often such whistles are so loud that they can be heard from our boats, with this scenario being particularly frequent amongst Short-beaked common dolphins (Delphinus delphis), charming cetaceans that dominated all the other tours of the day.
By Paula Thake
Sightings of the day
09:00 Unidentified baleen whale, Short-beaked common dolphins
13:30 Short-beaked common dolphins
09:00 Atlantic Spotted dolphins
15:30 Atlantic Spotted dolphins, Short-beaked common dolphins