Nice close-up shot of the pectoral fin of a whale indulging in the pec slap behavior on a calm February day outside the breakwater of Ma'alaea Harbor.
1 February 2013
Pec Slap behavior -- Humpbacks frequently indulge in rolling over onto their sides and forcefully slamming their long pectoral fins against the surface in a loud smack that sounds like small arms fire from a short distance off. Whales often punctuate a long series of pec waves with the occasional pec slap. Rather than being an aggressive activity, it's believed that pec slaps are meant to be an invitational display. I've seen similar behavior on the part of females participating in competition pods that would seem to support this interpretation.