Breeding of Pearls

Pearls are one of nature's most beautiful creations, commonly used as an element of women's jewelry. However, not everyone realizes that the process of obtaining pearls for industrial purposes is now largely controlled by humans.

Pearls are produced by mollusks—especially marine bivalves belonging to the pearl oyster family. They serve as a natural protection against irritation caused by foreign bodies (e.g., ubiquitous grains of sand) penetrating the soft mantle inside the shell. Concentrically arranged layers of nacre, composed mainly of aragonite, are secreted around the foreign body, gradually growing until a full pearl is formed. In cultured pearls, the introduction of a foreign irritating body is necessary to initiate the pearl formation process.

Initially, pearl divers would harvest pearl oysters (Pinctada margaritifera) from marine beds, bring them to the boat, open them, and check whether a given specimen contained a pearl or not. Opened shells were thrown back into the sea or taken to the port for mother-of-pearl production.

Nowadays, it is possible to look 'into the belly' of a pearl oyster using small X-ray machines. When interest in mother-of-pearl grew, pearls became the primary target of fishing. However, harvesting was so intense that pearl oysters became extinct in some regions. But as early as 1920, a Japanese man named Mikimoto developed a way to force pearl oysters to produce gems. A piece of epidermis is taken from a living mollusk, wrapped around a 'pearl nucleus'—ideally a piece of a Mississippi mussel shell—and implanted back into the foot of the oyster. After a few years, the 'nucleus' becomes covered with layers of nacre. Pearls obtained this way have commercial value after two years, while prime pearls require a wait of five years or more. Based on this method, the farming of so-called 'cultured pearls' developed on an industrial scale.

Cultured pearls have lower commercial value, although they are most often indistinguishable from natural pearls. This can be done using spectroscopic methods, where cultured pearls absorb less ultraviolet light. A cultured pearl will also have a trace of the implantation, the so-called nucleus. In the 1980s, the cultivation of the black-lip pearl oyster began in the Cook Islands region; this location was chosen because some atolls were particularly rich in oysters with black pearls. The Manihiki atoll was a leader in this regard, as its inhabitants had been involved in pearl and mother-of-pearl fishing for years.

Certain atolls of the Tuamotu Archipelago, as well as Tongareva and Suwarrow, also provide black pearls. In the 1980s, Manihiki became a 'pearl hub.' Pearl farms were established where pearl oysters live suspended on strings from underwater lines. From time to time, the staff inspects them, checks if they are thriving, ensures they are not attacked by parasites, cleans them of excess algae, and lowers them back into the sea. After several years, the pearls are harvested, and a new colony is established.