The great difficulty lay in removing the enamel-like plates which
are embedded in the strong pliable fibers of the hide and form a veritable
armor. This difficult was overcome at last and today there are a number of
companies engaged in the manufacture of shark leather and the marketing
of by-products. The meat makes good poultry feed and, because of its
high nitrogen content, is equally valuable as a fertilizer. The oil rendered
from the liver is used in paints, tanning, and other manufacturing
processes. Practically every part of the shark is used in some manner, even
the teeth which are utilized in the jewelry trade. (2 p. 278)

Of the ten species of sharks commercially useful, eight are
designated as Eastern: the familiar hammerhead, the tiger or leopard, the
mackerel, brown, black, tip, sand, blue, and the dusky. All have
differentiating characteristics and require separate handling methods
when caught. The nurse shark, also commercially valuable, has fins
which contain no gelatin and which are; therefore, without marked value
since soup cannot be made from them. The Tiger shark yields a greater
quantity of oil than other species which, on an average, produce about
four gallons each. (2 p. 279)

Thus it is that man has only recently found use for these
creatures which are one of the oldest life forms in the ocean. When the
face of the earth was little else than vast mud plains lying in seas of
uniformly warm water, some 350,000,000 years ago, the sharks were
present. As time went on, conditions became very favorable for them
until, in the Devonian Age, one of their kind became a great lumber-