27.09.2018 – Echoes in the east

Our spotter had spent the larger part of the afternoon scanning the Southwest waters of the island but wasn’t able to locate any animals in the area so our zodiac immediately headed east after leaving the marina. While covering a large search area we were finally informed of a group of cetaceans off the coast of Canico. At the location, we were able to enjoy a sighting with Short-finned pilot whales (Globicephala macrorhynchus) who were in the company of a handful of Bottlenose dolphins (Tursiops truncatus).

I had a wonderful group of interested guests on board who were eager to see but also speak about the animals. Amongst many of the characteristics addressed on board, we also spoke about the animals unique biosonar and how sound is produced and used by toothed whales. Odontocetes rely to a greater part on acoustic signals to socialize, hunt and navigate in the ocean. The use of high frequency sounds for navigation and locating prey is known as echolocation. Its use is confined to cetaceans and bats within the animal kingdom, both being creatures that forage and travel in environments where visual input is of little use. It was infact first described by Donald Griffin in bats and its use is confined to bats and cetaceans in the animal kingdom. These creatures send out high-frequency pulses and gain information from the returning „echoes“ that give them an accurate image of their surroundings. These echoes must be loud enough to return to the animal and short enough so that they return before the next soundwave is emitted.

We also had a biologist on board who had worked with bats and stated that they typically emit longer and a wider variety of signals to echolocate than dolphins do. The sound is produced in both the nasal passages and the mouth and directly received in the animals satellite shaped ears. Bats can discriminate the tiniest objects and obstacles whilst flying through dark areas using rapid high-frequency pulses that are not audible to human hearing.

In cetaceans sound is produced in the nasal passages just below the blowhole before it is modulated and focused in the melon, the animals fatty acoustic lens. The reflected soundwaves are then received in fatty tissue within the animals lower jaw that further transmits the signals to the animals ear. In the case of the Sperm whale (Physeter macrocephalus) a large organ known as the spermacetiis responsible for focusing produced sound waves. The highly sophisticated auditory system of dolphins allows the animals to emit signals of short duration, audible to the human ear as a series of clicks that start to sound like a continuous buzz as the animals approach objects in the water. Dolphins can detect targets at ranges of up to 100m and can assess the shape, size, material composition and internal structure of whatever they may be assessing.

Echolocation is extremely interesting but nonetheless a sort of abstraction for us humans. This is due to the fact that we greatly rely on visual signals for orientation and also when we socialize with one another. Blind people, however, live a more acoustic life and may rely on sound to the same extent that echolocating animals do.

So when we look out onto the ocean at night, we can only ponder on what a wide variety of buzzes, squeaks and clicks must be echoing in the darkness.

By Paula Thake

Sightings of the day

Ribeira Brava

13:30 No sighting

Stenella

15:30 Bottlenose dolphins, Short-finned pilot whales