12.10.2019 – Divergence

The majority of the sightings we enjoy during our whale-watching tours here in Madeira involve members of the toothed whale family (Odontoceti), a diverse group of cetaceans that are usually encountered as social units. Most of these species can easily be identified at sea due to obvious differences in appearance and behavioural patterns. Moreover, slight variations in the distribution of a species can even lead to visible changes in morphological features within a population and  lead to the creation of so-called ecotypes. An ecotype is a distinct race within a species that occupies a different ecological niche leading to an evolutionary process known as divergence. Today we meet two species that are both frequently sighted at this time of the year and both of which are known to contain different ecotypes.

The Short-finned pilot whale (Globicephala macrorhynchus) is thought to be a species that consists of three distinct types; the Shiho, the Naisa and the Atlantic types. Generally the species is scattered across the tropical, sub-tropical and temperate latitudes within the worlds oceans with the Shiho type dominating the eastern Pacific and the Naisa type occurring in the Western Pacific and the Indian Ocean. Naisa ecotypes are also encountered in the Atlantic region, meaning that we may encounter both the Atlantic- and the Naisa Short-finned pilot whales here in Madeira. This research is based on genetic variation amongst the ecotypes and very subtle morphological differences, which are difficult to determine on the field even during close encounters involving these large, gentle cetaceans like the one we enjoyed today. Since the animals are well-documented on the island perhaps ongoing research will provide proof that individuals of both ecotypes actually visit Madeira’s waters.

The Atlantic spotted dolphins (Stenella frontalis) we met today were as charismatic as ever, their behaviour creating a playful contrast to that of the lethargic pilot whales. Like the Bottlenose dolphins (Tursiops truncatus) occurring around Madeira, there are coastal as well as offshore ecotypes of these small delphinids in the Atlantic Ocean, with the latter being smaller and less spotted. These two ecotypes have been reported around the Bahamas but insufficient data on the populations of these seasonal visitors here in Madeira hasn’t enabled researchers to confirm sightings of both types. Irrelevant of the ecotype, these cheeky dolphins never fail to make our guests smile and we are always reluctant to watch them leave the islands waters as the warmer season gradually draws to a close here in Madeira. 

By Paula Thake

Sightings of the day

Stenella 

10:00 Atlantic spotted dolphins, Short-finned pilot whales