Narwhal fluke design helps compensate for drag caused by tusk

The spiral tusk of the male narwhal can weigh as much as 22 pounds and reach 9 feet in length. Now scientists have determined that pushing their tusks through the water has, over millennia, changed the shape of the other end of the narwhal—its flukes.

Image right: These CT topograms illustrate the differences in shape between female (top left and right) and male (bottom left and right) narwhal flukes.

Using 3-D computerized tomography to study variations in fluke geometry between male and female narwhals, researchers have determined the variation is directly related to swimming performance. Male narwhal flukes have a slightly concave leading edge with no sweepback. Female narwhals have no tusks, and their flukes are similar to that of a dolphin, which have a swept back leading edge. The male’s fluke design helps it overcome the drag caused by their long tusks, the scientists determined. The female’s fluke design gives them increased speed for diving while foraging.

Image left: Narwhals tusking (Photo by Glenn Williams)

The researchers also studied cross sections of the flukes, which were legally obtained from aboriginal hunters in Canada. For both sexes of narwhal, the fluke cross-sections were highly streamlined, having a rounded leading edge and a tapering, trailing edge, the researchers say.

Scientists who participated in this study are Janet Fontanella and Frank Fish of West Chester University; Natalia Rybczynski of the Canadian Museum of Nature; Martin Nweeia of Harvard University and the Smithsonian’s National Museum of Natural History; and Darlene Ketten of Woods Hole Oceanographic Institution. Their findings were published in a recent issue of the journal Marine Mammal Science.

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