Some years ago, when I was assisting Dr. Dan Salden and Hawaii Whale Research Foundation during whale seaon in Hawaii, we came across a humpback whale (Megaptera novaeangliae) not far from Lahaina that showed considerable scarring, almost certainly from a boat strike. The most likely explanation for the series of thin, evenly spaced, parallel cuts is a boat propeller, making numerous slices along the dorsal ridge of the whale as the boat passes over the whale. The whale would have been at the surface, or just below the surface, for this to occur. It appears that the wounds have healed on this particular whale, and the whale did not show any evidence of disability that I recall.
North Pacific humpback whale showing extensive scarring, almost certainly from a boat propeller, on dorsal ridge.
Image ID: 05910
Species: Humpback whale, Megaptera novaeangliae
Location: Maui, Hawaii, USA