Humpback whales have always been characterized by their large pectoral fins. In fact their scientific name, Megaptera novaeangliae, translates to “big winged New Englander,” paying homage to their nearly 15 foot fins. These fins are specifically designed to be extremely hydrodynamic, allowing for easy movement through the water, despite their size. They are so efficient, that many wind turbine blades are designed based off of these fins.

Photo credit: CMWWRC Database 2012

Their pectoral fins are often used in social behaviors known as “pec slapping,” which is when a humpback whale will raise its pectoral fin up in the air while on its back or side, and slap it against the water. This behavior is believed to be a form of non-verbal communication for whales, which can be seen on both breeding and feeding grounds. Though it is unsure why exactly humpback whales pec slap, but there are several hypotheses. One is that it is a way that the whale shows frustration, while others suggest that it is a playful behavior.

Logistically, it has long been thought that the pectoral fins are used for steering, something these 45 foot mammals do exceptionally well, especially when their size is taken into consideration. However, a recent study done out of Stanford University suggests that humpbacks also used them for propulsion.

Photo credit: CMWWRC Database 2012

Using relatively new video tagging technology, researchers were able to study the movement of these whales in an unprecedented way. They were able to find that the whales would occasionally flap their fins like a penguin would while swimming underwater. This flapping would cause a very short boost in acceleration for the whale. The researchers believe that this is not something the whale can do frequently, due to the fact that likely requires a lot of energy, but can be very beneficial to the whale if it needs to travel short distances very quickly.

They also suggest that this propulsion is highly beneficial when lunge feeding, which is when a whale goes through a bait ball in a short burst of swimming with its mouth wide open. Like all other propulsion, it was always thought that this lunge was created by the undulation of the tail. But this study shows that, in some instances, it may be caused by the flapping of the pectoral fins.

The study also notes that it is likely that humpbacks are the only species capable of using this flapping mechanism for propulsion, because they are the only marine mammal with pectoral fins long enough to create such propulsion.

-Andrea Jelaska, Intern at Cape May Whale Watch and Research Center, Wheaton College

Sources:
https://www.sciencedaily.com/releases/2017/07/170710122926.htm
http://www.cell.com/current-biology/fulltext/S0960-9822(17)30629-2?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982217306292%3Fshowall%3Dtrue