24.07.2019 – Salty

I had the pleasure of guiding the tours on both our vessels today and on both tours we encountered one of my personal favourites, the Atlantic spotted dolphins (Stenella frontalis). My encounters with these dolphins, both in and outside the water, have inspired me to learn so much more about these animals and their remarkable abilities. The more you read about dolphins, the more they appear as the most sophisticated and intelligent beings of our oceans, learning from their mistakes and actively mastering their own personal development, manifesting characteristics that challenge even our own social capabilities. There is, however, one question which still makes scientists scratch their heads; do dolphins drink?

Drinking itself is actually a form of osmoregulation, where we control the amount of water in our bodies by ingesting water and other water-containing liquids to keep ion concentrations in our bodies at healthy levels. Like us, marine animals need to maintain a certain concentration of fresh water in their bodies in order to survive and, because they inhabit a saltwater environment, regulating this can get bit tricky. Some animals actually drink sea water and excrete excess salt, like different species of marine fish, who get rid of it through their gills and sea turtles who have salt glands under their eyes allowing them to “cry” highly-concentrated saltwater. Dolphins are thought to drink through ingestion of prey and have an increased urine flow rate, excreting all the excess salt and keeping the freshwater in their bodies. 

What about animals that inhabit saltwater environments but don’t actually live in water, like marine birds? Well, here the incredible family of the Tubenose marine birds comes into the picture, with its most frequently encountered member out at sea here in Madeira being the Cory’s Shearwater (Calonectris borealis). This bird doesn’t only entertain with its strange calls at night, reach an incredible age of 50 years and cover inconceivable distances during its migratory flights; these highly pelagic birds can also actually drink seawater! The excess salt is excreted through a gland near their eyes which is only active in members of the Tubenose family, making this highly vulnerable family of marine birds a tad more resilient than others out at sea. No wonder our Stenella tour in the afternoon contained some self-proclaimed Cory-Fans this afternoon and after sharing some of the facts on these birds, I hope I encouraged this fan club to grow!

By Paula Thake

Sightings of the day

Ribeira Brava

09:00 Atlantic spotted dolphins

Stenella

15:30 Atlantic spotted dolphins, Loggerhead turtle