05.09.2021 – High & low riders

Many hunt in the deep but they all need the air; cetaceans truly are the oceans masters when it comes to living at the interface of the two elements. Their life cycles, social lives and prey preferences, however, determine how much of their time they spend at the surface and how much of it is spend travelling through the darker depths of our oceans.

Beaked oceanic dolphins like the Atlantic spotted dolphins (Stenella frontalis) and the Bottlenose dolphins (Tursiops truncatus) belong to the high riders, since they spend most of their time at the surface or within the first few metres of the water column. If the spotted dolphins would cruise through deeper waters, we wouldn’t be able to appreciate them during our snorkelling tours like we did this morning. Bottlenose dolphins also travel at the surface but often dive to hunt in the darker layers of the water column. Both species were encountered on our Stenella tour this morning, along with Short-finned pilot whales (Globicephala macrorhynchus), a species we also met further west in the afternoon.

Pilot whales are the intermediates when it comes to life at the surface and in the deep. The animals cruise, socialise and rest at the surface and dive to hunt at incredible speeds in the deep. The deepest dive by a member of the species recorded in Madeira was 990m deep and only lasted 15 minutes! Such sprint dives have earned these impressive cetaceans the nickname cheetahs of the ocean, an attribute which is rarely appreciated at the surface.

The last species encountered today represents another extreme; beaked whales generally prefer doing everything in the depths from feeding up to socialising. They even are thought to only begin communicating in the deeper layers of the water column to avoid predation by Orcas (Orcinus orca). Although the Blainville’s beaked whales (Mesoplodon densirostris), the species we met today, are known to be curious and more approachable than other beaked whales they still definitely belong to the low rider cetaceans.

By Paula Thake

Sightings of the day

Stenella

09:30 Atlantic spotted dolphins (snorkelling), Bottlenose dolphins, Short-finned pilot whales

15:00 Blainville’s beaked whales, Short-finned pilot whales