Fish scale the surface, interacting only with the riblet tips, not causing any high-veloctiy flow in the valleys. Since this high velocity flow now only interacts with the riblet-tip, which is a very small surface area, the momentum transfer which causes drag is now much lower than before, thereby effectively reducing drag. Also, this reduces the cross-stream velocity fluctuations, which aids in momentum transfer too. The rough, sandpaper-like texture of shark and ray skin, coupled with its toughness, has led it to be valued as a source of rawhide leather, called shagreen. One of the many historical applications of shark shagreen was
Kangaroo leather in splits. Bovine skin is much more complex in cross section. Hence in whole section it has many more weak points from which tears can start when placed under tension. In addition when sliced into splits the collagen fibres running at significant angles to the skin surface will be cut. These then become weak points in the structural strength. The Australian kangaroo industry produces a range of meat and leather products from animals harvested from the wild under strict government controlled Management Plans. These ensure the harvest is sustainable and humane. A wide cross section of Australian ecologists support the