The flow induced by a mock whale : origin of flukeprint formation

Fluke oscillations of cetaceans (whales, dolphins and porpoises) imprint the ocean surface with an oval patch that surface waves cannot enter. Scientists have hypothesized that modification of surface tension by surfactants creates flukeprints. Here, we show, on the contrary, that the formation of flukeprint is primarily due to a wave-current interaction problem. We provide Particle Image Velocimetry measurements of anisotropy and vorticity in the flow generated by a mock whale fluke in a laboratory experiment. We explain for the first time why long gravity waves enter the flukeprint, whereas short gravity waves are blocked.