24.09.2018 – Voices in the depth

There has not been a lot of activity in the waters South of Madeira today. Anyway, after hours of searching from land and sea some long oval shapes came into sight not too far off the bow of our traditional fishing vessel. The lighter or darker brown coloration as well as the relatively small dorsal fins indicated that there were Blainville’s beaked whales (Mesoplodon densirostris) around.

Those animals regularly dive for 45 to over 60 minutes into depths averaging around 800 meters.  They prepare for their long dives by spending extended periods of time near the surface. This is the best moment to observe them and we were lucky to encounter the animals in that phase during our tour today.

Blainville’s beaked whales hunt and feed in the depth. They echolocate their prey during these deep foraging dives with specifically modulated click and buzz sounds. In the initial search and approach phase, the inter-click intervals are long (0.2 to 0.4 s) and can be compared to chirp signals of bats. The strong echo returned is traded for rapid updates in the terminal phase when one or more targets are within approximately a body length of the whale (2 to 5 m). Very fast buzz sounds, also reported from large delphinids, increase the temporal resolution and enable the deep-diving animals to finally get hold of their prey.

A hungry beaked whale needs a well-developed strategy to find a meal in the complete darkness of the deep sea. It´s their voice that makes the difference in the depth.

by Jan-Christopher Fischer

Sightings of the day

Ribeira Brava

13:30 No sightings

17:00 Blainville’s beaked whales