As a long time student of marine biology, I have to say that it saddened me to see the "Reef Rapers" come to collect live coral, sea shells (with the animals still alive inside), sand dollars, shark jaw collectors, conch, you name it. Most of the time it was to make money from selling these things to tourists. Every morning I would find several carcasses lying on the beach with jaws cut out. It has died down since the movie Jaws - and its sequels, but still prevalent. Black and Red coral necklaces, sea shells and sand dollars are still being sold. Please don't buy these things, it only supports the purveyors. Pass the word.
Shark cartilage is desirable for its purported anti-cancer qualities.
NCI Cancer Bulletin for July 26, 2005 (HTML) - National Cancer Institute
Sharks have one of the lowest incidences of cancer of any living creature. They have evolved over millions of years and are a necessary part of the food chain.