Our snorkelers had the chance of gliding alongside a calm, curious group of Atlantic spotted dolphins (Stenella frontalis) this morning and, as if that wasn’t enough, also managed to end the tour with a small group of Short-finned pilot whales (Globicephala macrorhynchus)! While the spotted dolphins are more abundant during the summer months, pilot whales belong to the species of cetaceans that can be encountered all year round in Madeiras waters. Scientists have even identified groups of resident animals that return to the archipelago time and time again. Summer, however, is an interesting time for both the spotted and the pilot whales since both species enjoy feeding on the abundant deep-sea squid that migrate from the dark ocean to the surface at night. In summer the upper layer of the ocean heats up, trapping nutrients close to the surface that otherwise rain into the deep. This results in an enormous migration of mesopelagic animals to the surface at night, making several a delicious and easy prey for cetaceans. Some of the spotted dolphins had especially dark faeces today, which may be due to the ink in the squid they had ingested only hours before.
Pilot whales are deep-diving dolphins and are generally considered to be expert hunters of squid, with some cetacean scientists even assuming that the species may compete with Sperm whales (Physeter macrocephalus) in hunting for giant squid in the abyss. The streetwise Bottlenose dolphins (Tursiops truncatus) are also aware of this fact and often socialise with the pilot whales in deeper waters, probably hoping to gain some hunting advantages in catching this nutritious and hydrating prey. The Bottlenose we encountered this afternoon weren’t socialising with any other species but instead balanced the lively, interactive nature of the spotted dolphins during that same trip with their subtle curiosity. After returning to the marina at the end of the day, I couldn’t help but imagine the animals we encountered today hunting the squid in the darkness.
By Paula Thake
Sightings of the day
09:30 Atlantic spotted dolphins, Short-finned pilot whales
15:00 Atlantic spotted dolphins, Bottlenose dolphins