Pectoral fin slapping, commonly referred to as “pec slapping”, is when a humpback whale that is swimming on its side or back at the surface repeatedly raises its pectoral fin into the air and drops or swings it back to the surface to produce a large splash and loud report. Along with breaching and lobtailing, pec slapping is one of whale watcher’s most popular surface behaviors to observe.
Sometimes the whale will simply let the pectoral fin drop, other times the whale will exert itself for greater impact. Since the pectoral fins are up to 15 feet in length, the results can be very impressive, indeed!
Like breaching and lobtailing, pec slapping is believed to be another form of non-verbal communication and is frequently seen in the social context of the breeding grounds of the Silver Bank. Courting whales may slap their pec fins to attract attention. For example available females may slap their fins provocatively when in the company of one or more males, often with explosive results.
Humpback whales have a powerful ball and socket joint where the pec fins attach to their bodies, much like a human shoulder, giving the fins a remarkable range of motion which allows the fins to be slapped either dorsally or ventrally, singly or in pairs, alternating or in parallel.