Shark Problems (from a human’s viewpoint) 179
the accuracy. Plugging these measurements into a published table with
equations for different shark species then gives a highly accurate estimate
of shark length.
How can sharks be repelled?
Perhaps this question should be rephrased as “Is there such a thing as
an effective shark repellant?” The answer is yes and no. It depends on the
shark and, more importantly, the circumstances. Curious sharks can be dis-
couraged, and sharks that are leisurely feeding can sometimes be made to
cease feeding, but actively feeding sharks (the ones we may be most con-
cerned with) usually ignore any and all repellants.
Several natural chemicals that sharks appear to avoid or are repelled
by have been tested. It has long been known that sharks avoid dead, rot-
ting shark carcasses; the chemical or chemicals involved have been sought
and tested, again with varying success. After World War II, the U.S. Navy
provided packets of Shark Chaser, which consisted of cakes of what was
thought to be the active ingredient in dead shark, copper acetate, com-
bined with dark nigrosine dye. When dissolved in water by a downed pi-
lot, the dye-chemical combination shrouded the diver at least visually and
repelled any nearby sharks chemically. Tests showed that Shark Chaser
worked about two-thirds of the time on a variety of sharks, but at other
times, sharks were as likely to bite down on the cakes as avoid the area.
Other chemicals have been tried, again with varying success. Sea cu-
cumbers secrete a substance called holothurin that results in rapid avoid-
ance by some lemon sharks. A flatfish from the Red Sea, Pardachirus mar-
moratus, secretes a substance that sharks find repulsive (see “How do sharks
find food?” in chapter 7). The active ingredient, a surfactant (like soap),
and similar chemicals have been tested, although they have to be squirted
directly at an approaching shark, an action that becomes tricky in an attack
situation. Physical barriers have included a large, heavy-duty plastic bag
with a floating ring on top developed by the U.S. military called the Shark
Shield (less formally referred to as the whole-body condom). A swimmer,
diver, or downed pilot climbs into the Shark Shield and theoretically de-
creases some of the signals given off that sharks find attractive. Other prod-
ucts include sonic guns and bubble curtains (variously repulsive or ignored).
A patent was granted in 1985 (U.S. Patent 4,494,245) for a shark-repel-
ling wetsuit colored with boldly contrasting stripes or bars that mimic the
warning coloration of sea snakes. The idea is that a shark seeing this would
associate the color with that of the poisonous snake (and many other nox-
ious animals) and therefore leave it alone. We contacted the patent holder,