20.09.2020 – Acoustic fingerprint

The expanse of the southwestern waters seemed like a desert today and, although we kept a sharp eye on the activity of passing Bulwer’s Petrels (Bulweria bulwerii) and Cory’s Shearwaters (Calonectris borealis), our team only managed a sighting of a young basking Loggerhead turtle (Caretta caretta) this morning. Since the western waters seemed void of cetaceans, our spotter decided to lead both our boats to the waters further east outside Ribeira Brava this afternoon.

Here our Stenella managed to meet both species of dolphin that we are permitted to snorkel with; the Atlantic spotted dolphins (Stenella frontalis) and two Short-beaked common dolphins (Delphinus delphis). While the spotted were moving in a large group of over 70 animals and curiously approached our boat, the common dolphin mother and her calf kept their distance. The common dolphins tend to be more abundant during the winter months with only tiny groups with calves remaining in the sheltered waters of the archipelago.

To stay together, dolphins constantly communicate with each other through a series of vocalisations which also include signature whistles, high-pitched calls that help the animals recognise and locate each other in the water. Signature whistles are particularly important for mothers and calves to prevent them from getting separated and have been recently been used in abundance studies of dolphins. These acoustic fingerprints may be another alternative to photo-identification and help scientists track different cetacean populations, including endangered ones.

Doing this with Blainville’s beaked whales (Mesoplodon densirostris) will be more of a challenge. The animals only communicate in the deep to avoid predation by larger toothed whales such as orcas and are extremely timid in nature, a characteristic that was clearly visible during this afternoons sighting on the Ribeira Brava. Nonetheless the more non-invasive tools scientists have at their expense to conduct long-term research on cetaceans, the more we can learn about them in future.

By Paula Thake

Sightings of the day

Ribeira Brava

15:00 Blainville’s beaked whales, Short-beaked common dolphins

Stenella

10:00 No sighting

15:00 Atlantic spotted dolphins, Short-beaked common dolphins