17.10.2018 – The appetite of the Sperm whales

Today we went out two times with “Stenella” and managed to see plenty of cetaceans around our zodiac in the morning as well as in the afternoon. Apart from big and partially mixed pods of Bottlenose dolphins (Tursiops truncatus) and Short-finned pilot whales (Globicephala macrorhynchus), we also found relatively big groups of Sperm whales (Physeter macrocephalus).

Those grey-brown giants feed in the depth. Their prey consists mainly of mollusks, deep sea squid makes up around 80% of their diet. But those skilled hunters also predate on big fish species, crustaceans and even sharks. One characteristic feature of the Sperm whales is their strong gender dimorphism. Females can reach body lengths of up to 12 m whereas male Sperm whales get significantly bigger. They can grow up to 18 m and their body mass is with over 40 t more than twice as big in comparison to the female animals.

Those massive bodies require some energy and therefore Sperm whales consume good amounts of food. The image of the whale with the big head fighting against Giant squid (Architeuthis dux) is real but doesn’t represent the everyday foraging routine of the animals. Very big mollusks are rare and contribute only marginally to the diet. In fact, the Sperm whales are more collectors than hunters. Their food consumption can be compared to a man of 90 kg eating portions of the size of walnuts. Those are smaller squid species which make their daily bread.

One special highlight of the day has been a pod of very fast moving and jumping Pilot whales which were traveling offshore in the late afternoon. The reason for this rare behavior remains speculative. It has been the first time this summer for us to witness that.

by Jan-Christopher Fischer

Sightings of the day

Stenella

10:00 Bottlenose dolphins, Short-finned pilot whales, Sperm whales

15:00 Bottlenose dolphins, Short-finned pilot whales, Sperm whales