After a long time waiting for optimal sea conditions, we finally have been able to carry out an exclusive trip for our Intern biologists’ team. Trips like this allow us to spend more time taking data than on our regular whale watching tours. This is also a great opportunity to learn and improve our sampling techniques. In particular, today we have focused the trip on acoustic data collection using hydrophones.
We started our trip from Ponta Delgada as usual, getting important information from the lookouts. Rapidly we managed to find a group of around 30 common dolphins swimming near the shore, so we could start using the hydrophones to try to hear them.
The hydrophones are special microphones that work underwater, so they allow us to listen to the sounds whales and dolphins emit, either to communicate with each other or to hunt and orientate themselves. Here in Futurismo we use two types of hydrophones, one of them has an external bowl attached to it, which allow us to use it directional. That adaption helps us detecting where the sound is coming from while we turn it steadily underwater and then we go and search for the animal in the according direction. The other hydrophone we connect to a recorder and loudspeakers to record sounds all around for research and also for educational purposes.
After the first tests with the dolphins, we continued in hope of sperm whales, which were our main objective to collect more data to aim to study these records to calculate a size estimation of these sperm whales.
We continued the trip to the east of the island, looking for them. We were so lucky to find two already known sperm whales: Orca, she has a big white patch on her back, and Dilys. These two sperm whales were already identified by Futurismo, one belongs to what we call the red unit and the other one to the green unit.
At Futurismo, we have been able to recognise numerous sperm whales, which we have grouped into units according to the sightings we have made, with the idea of understanding the social structures of these animals frequenting the waters off the south coasts.
Each unit is assigned with a colour to make it easier for us to understand who tends to hang out with whom. Surprisingly we found these two individuals which normally are not sighted together but we will definitely keep an eye on them and check if there will be further overlaps in sharing their habitat at the same time as we already had noticed connections between certain units before.
During sightings, we take advantage of the moment they stay on the surface to take photos for our photo-identification. It is when they dive when we use the hydrophone to record their sounds.
While recording the sounds of the sperm whales we realised that many individuals were foraging at the same time. The spectrogram showing the sound was crowded of broadband frequency “clicks”, though the most intensive clearly belonged to the closer individual, which we started recording just at the beginning of its dive.
These clicks, ranging from 5 to 25 KHz, are produced in the head of the whale by phonic lips and are then amplified and directed in the spermaceti organ. The sound that travels towards the prey, bounces off and returns to the emitter providing information of the distance and characteristics of its prey.
The spectrogram displays the echolocation sound, the more intense in colour belongs to the targeted individual. Nevertheless, the foraging “clicks” become more frequent as the hunter approaches its possible prey. Before a catch the sound changes to rapid click buzzes called creaks but this we did not recorded in this sample. More clicks result in more echoes which are providing broader information of the prey as it became interesting to be eaten. Finally, a short silence after the not recorded buzzes can mark the prey’s capture. This specialised foraging let us wonder, how on earth they manage to distinguish their colleagues “clicks” from their own ones?
On this trip, in addition to the photography and acoustic work, we also had the opportunity to observe other marine species.
Apart from the various common species of seabirds such as the Cory’s shearwater or the yellow-legged gull, we were also able to get close to a loggerhead turtle. Sargassum, which is a seaweed and big numbers of Portuguese man of war had been dragged by the wind and sea currents and spread over vast extensions.
As the cherry of the cake, we found a violet sea-snail, which is also called common violet snail (Janthina janthina), floating upside down on the water surface thanks to a self made bubble raft. This special sight was the first documentation for our company of this species which preys on Portuguese man of war and Velellas also called purple sails. Isn’t it funny that the violet sea-snail is eating the purple sails? So with the abundance of Portuguese man of war it had plenty of food to go for.
We are now looking forward to discover even more about marine life and enjoy it with you. Come and join us to learn something new about the whales and dolphins and the other wildlife surrounding our island!
Acoustic equipment was donated by Idea Wild.
Written by Mireia Espuñes Capdevila, Jorge Pan Martinez and Melissa Guinnot Sánchezn.