27.11.2018 – Humble solitude
When we think of cetaceans we think of highly social and intelligent animals, gracefully wandering the oceans in each others company. The Striped dolphins (Stenella coeruleoalba) we saw on the Ribeira Brava trip this morning fit that description perfectly with their incredible group dynamic and their swift, synchronized leaps.
However, not all cetaceans travel in groups. The species belonging to the family of the baleen whales (Mysteceti), as opposed to the toothed whales (Odontoceti), generally embark on their long journeys alone. The migration routes of these large filter-feeders are said to be dominated by plankton blooms in designated feeding grounds. It is in these grounds where the whales are seen in the company of their peers and where social behaviour amongst the animals can be observed.
We hadn’t seen a baleen whale in quite a while so we were overjoyed with the sighting of a massive (and rather curious) Sei whale (Balaenoptera borealis) on the Stenella tour this afternoon. This species can be encountered throughout the year in Madeira but the animals tend to be more abundant in winter, where they migrate from cooler, subpolar waters to warmer subtropical latitudes. In spring the animals head back to the North Atlantic along the continental slope
Their long and rather lonely migrations don’t, however, stop baleen whales from communicating with one another. As opposed to the short-frequency soundwaves used in close range by toothed whales, baleen whales emit low frequency calls that echo across ocean basins to their peers. Recorded contact calls by Sei whales had frequencies as low as 34Hz while Blue whale (Balaenoptera musculus) calls hold the record of being the loudest and deepest in the animals kingdom, ranging between 10-40Hz. To put things into perspective, the lowest frequency audible to the human ear is 20 Hz.
Some marine loners, however, can not communicate over such distances and spend their lives in unassuming solitude. For the first time in around two months we encountered a basking Loggerhead turtle (Caretta caretta) that was spotted by the birthday girl on board the Ribeira Brava this morning. Turtles generally live a solitary life and embark on incredibly long journeys through the worlds oceans. The animals frequenting Madeira are mainly juvenile turtles that come to these waters to feed and rest. Although the routes of species aren’t as fixed as those of the baleen whales, their migrations are far from random and depend largely on ocean currents. Their phillopatric nature also bids them to return to the very same beach where they had hatched to lay their own nests.
The phrase “not all who wander are lost” is therefore widely applicable to the magnificent creatures of our oceans.
By Paula Thake
Sightings of the day
10:00 Striped dolphins
15:00 Sei whale