Sharks and Humans 161
One exception is sawfish snouts, which are employed in Chinese traditional
medicine as a cure for heart disease, infections, parasites, weakness, and
blood thinning. This use has fueled an unfortunate modern trade in saw-
fishes despite their endangered status and international protection.
Another alarming and recent exception involves manta rays and their
relatives, which have found their way into Hong Kong markets in increas-
ing numbers because of a demand for their gill plates. Mantas filter zoo-
plankton out of the water with their gill plates (see the discussion of filter
feeders in “How do sharks catch their prey?” in chapter 7). Proponents of
manta medicine claim that eating gill plate soup, called “peng yu sai,” can
aid in the treatment of asthma, skin rashes, chicken pox, and, again, can-
cer. The erroneous logic applied is that since mantas filter food from the
water, gill plate soup can filter and detoxify diseases from a person’s body.
There is absolutely no evidence to suggest that any of these benefits are
real. Sadly, whereas only a limited market existed for mantas before (the
meat is eaten in a few areas), they are now hunted extensively and in large
numbers to feed the gill plate trade.
Sharks do produce one substance used in anticancer drugs. The active
chemical is called squalamine and was first isolated from shark livers, stom-
achs, and gall bladders, not from cartilage. Squalamine has proven effective
(To p) Untold numbers of sharks
are killed each year to extract chon-
droitin from their cartilage to make
cartilage pills, a product that can be
made from many other, less threat-
ened sources. (Bottom) But you can
feel good because the outer capsule
is made from vegetable matter, and
the entire process is eco-friendly
because it’s wind-powered. Photo by
Gene Helfman