This publication talks about Humpback whale (Megaptera novaeangliae). In particular, we are going to do an small introduction and we are going to focus on feeding behaviour of this animal, specially in a particular strategy devoloped for a group in west coast of Alaska.
Humpback whale, Megaptera novaeangliae, is a cetacean of the Balaenopteridae family that live in all the oceans, in oceanic and coastal waters. They measure between 12 and 16 meters (the females are lightly bigger than males) and they weight between 25 and 35 metric tons. They eat krill and fishes. We can identify them using different things: the caudal fin, with a visible central groove and with a cut edge, raises before it dives; the pectoral fins are very big and rounded, with a dark top and light bottom; the head is wide and has nodules on the top and also has nodules on bottom mandibule; and they have a big body, with a black – dark grey back and sides and a white abdomen.
About feeding behaviour, they have developed different amazing methods. The most known is called the bubble net, used to capture shoals of fishes. Other least sophisticated methods consists on swim against the fishes or hit the water with fins to stun them.
Now we are going to talk about the net bubble method. This one has been observed in a population from west coast of Alaska. During the summer, in the Alaska’s fjords there is a lot of plancton, what attract the herrings (Clupea harengus), which used to live in the depths to be protected from the predators. When humpback whales detect the fish, they do jumps and hits to advertise the other members. This method needs a lot of coordinaiton. Following the leader, they dive together and then each one adopt its position: there are the shepherds, who surround the shoal with fin movements with the goal of avoid the fishes escape; another member is placed under the shoal and produce a shout of 120 decibels to force the fishes to go up; and there is another member in the top that expel an air current to create a bubble net. The other members are under the fishes and jump against them with the mouth totally open. This technique allows to capure a half ton of fish every day.
Author: Richard Palmer
I recommed seeing this video:
If you want more information, you can look for it here:
– DAY, Trevor. Guía para observar ballenas, delfines y marsopas en su hábitat (Ed. Blume)
– KINZE, Carl Christian. Mamíferos marinos del Atlántico y del Mediterráneo (Ed. Omega)
– PERRIN, W. F.; WÜRSIG, B; THEWISSEN, J. G. M. Encyclopedia of Marine Mammals (Ed. Academic Press, 2ª edició)
– Gigantes del mar, episodi 2: http://www.youtube.com/watch?v=lSQ6d02L1jc