23.10.2018 – Chasing rainbows

We set out west of Calheta this morning, with a group of very excited guests aboard our Stenella while admiring a double-rainbow curving elegantly over the Atlantic. The isloated showers on the ocean didn’t make things easy for our spotter to follow the small group of Bottlenose dolphins (Tursiops truncatus) off the coast of Jardim do Mar he had seen earlier. After searching for some time we decided to head out into the open ocean to go find some Sperm whales (Physeter macrocephalus) instead and managed to observe one animal briefly logging before it dove into the depths of the Atlantic.

Besides the whole delight of seeing their enormous lifted fluke, there is something magical about watching a Sperm whale dive and we talked about this a little bit on board. Apart from their acute bioacoustics used for orientation and hunting, deep-diving cetaceans like Sperm whales and beaked whales posess several anatomical and physiological adaptions to spend an ample amount of time in the dark ocean.

Cetaceans generally breathe less frequently than terrestrial mammals and exhale up to 80% of the air they inhale, almost completely emptying their lungs. Infact, before a Sperm whale plunges into the deep to hunt for giant squid, it exhales completely pressing all the air out of its lungs. This allows its flexible rib-cage to fold onto itself, a foundational adaptation for such deep-dives along with the vast amounts of elastic tissue in their lungs that helps prevent possible pleural damage. The oxygen used for powering the animal during its foraging activity is gained from the pigment Myoglobin, which is directly located in the animals muscles and retains alot more oxygen than haemoglobin. Additionally, the animals circulatory system is able to withstand the extreme pressure differences due to the vast amounts of elastic tissue surrounding its vessels. Moreover strategically placed capillary networks, forming part of a unique blood vessel framework known as the Reta mirabile, help control blood pressure during deep dives.

After enjoying sightings with these deep divers amongst the double rainbows in the morning, the skies cleared and gave way to warm sunshine for our afternoon trips. The better conditions allowed our spotter to locate a large group of Striped dolphins (Stenella coeruleoalba), a beautiful oceanic dolphin that is notorious for travelling in large schools across the high seas.

By Paula Thake

Sightings of the day

Ribeira Brava

14:30 Striped dolphins

Stenella

10:00 Sperm whale

15:00 Striped dolphins