Black pearls have never been found in the quantities of white pearls. Nevertheless, for centuries Mexico was a prodigious supplier of this variety. Cortez, the first Westerner to hunt for black pearls with systematic determination, had two species of pearl oyster to choose from: the Pinctada mazatlanica (La Paz black-lipped pearl oyster) and the smaller but more colorful Ptenia sterna (Western Winged rainbow-lipped pearl oyster). Not only were these mollusks plentiful, they prolifically produced pearls, often as many as 14 out of every 100 shucked oysters.

    Because of its oyster plentitude, Mexico was known for nearly four centuries as the world's sole and then later primary source of black pearls-gradually giving way to Tahiti after 1850. Most Mexican pearls came from the west coast state of Sonora where the Gulf of California's pearl fisheries are located. Between 1827 and 1874, Mexico shipped 500 metric tons of pearl shell to Europe every two years. One can only imagine the accompanying volume of pearls.

    In 1874, Mexico's pearl production briefly surpassed old peaks with the introduction of diving suits that allowed divers to go deeper and gather oysters for longer periods of time. For the next decade, divers raided the most populous pearl beds. As oyster retrieval rates began to exceed reproduction rates, overfishing rapidly wiped out Sonora's pearl fisheries.

    It didn't help that female oysters were much larger than males (oysters are herma-
phroditic, starting life as males and then becoming females), which made them more likely targets for divers. With fewer and fewer females, it was only a matter of time before oyster stocks were depleted.

    By 1900, Mexico was a pearl-producing has-been.