02.03.2019 – Taking the plunge
Our search for cetaceans took us far out to sea during the todays tours in the morning as well as in the afternoon. In the morning the Stenella crew was able to track down a group of Bottlenose dolphins (Tursiops truncatus) off the far western coast of the island. While several animals, particularly calves, approached our bow and socialized amongst one another, others were busy hunting schooling fish at the surface. Occasionally, however, dolphins do dive a little deeper to search for prey and this is done either for selective reasons or due to absence of sufficient prey at the surface. Such prey may include fish that tend to swim deeper within the water column or even deep-sea squid. Current knowledge on Bottlenose dolphins allows us to assume that the animals can reach a depth of up to 500m, which is certainly an achievement for such a surface-active cetacean.
Bottlenose dolphins often seek the company other deep-diving cetaceans that actively hunt squid, such as that of Short-finned pilot whales (Globicephala macrorhynchus), to ensure the success of these energetically expensive foraging dives. Marine birds also follow a similar scheme. Madeira is visited by several members of the Tubenose (Procellariiformes) family, particularly the Cory’s shearwater (Calonectris borealis). These highly-pelagic, intelligent creatures often follow cetaceans during their daytime search for prey at the ocean surface and even help our team locate possible marine mammal activity from afar. The Corys, however, do this out of convenience not necessity. The animals can dive down to depths of up to 15m if required!
While our afternoon tour on the Ribeira Brava unfortunately ended without a sighting of cetaceans, we were able to witness a rare spectacle involving yet another formidable diver in action. A juvenile Northen Gannet (Morus bassanus) had clearly chosen the islands waters for a pitstop during its spring migration and was foraging off the western waters of the island. The largest of the gannets is notorious for its impressive plunge dives when it detects prey, during which it can reach speeds of up to 65km/h! We watched in awe as the juvenile shot into the ocean from about 8m in the air and surfaced before clumsily taking flight off the surface. The Atlantic didn’t make our search for cetaceans easy today but was nevetheless generous enough with these fantastic sightings!
By Paula Thake
Sightings of the day
10:00 Bottlenose dolphins
15:00 No sighting