In 1735, the Spanish admiral, Antonio de Ulloa visited the Panama pearl fisheries and wrote an extended description of them.[284] According to his account the pearls were then found in such plenty that there were few slaveholders in the vicinity who did not employ at least a portion of their Negroes in the fishery. These were selected for their dexterity in diving, and were sent to the islands in gangs of from eight to twenty men each, under the command of an overseer. They lived in temporary huts on the shore, and visited the pearl reefs in small boats. Anchoring in eight or ten fathoms of water, the Negroes would, dive in succession to the bottom, returning with as many oysters as possible. It was laborious work, attended with danger owing to the numerous sharks. Every one of these Negro divers is obliged daily to deliver to his master a fixed number of pearls; so that when they have got the requisite number of oysters in their bag, they begin to open them, and deliver the pearls to the officer, till they have made up the number due to their master; and if the pearl be but formed, it is sufficient, without any regard to its being small or faulty. The remainder, however large or beautiful, are the Negro’s own property, nor has the master the least claim to them, the slaves being allowed to sell them to whom they please, though the master generally purchases them at a very small price.... Some of these pearls, though indeed but few, are sent to Europe, the greater part being carried to Lima, where the demand for them is very great, being not only universally worn there by all persons of rank, but also sent from thence to the inland portions of Peru.[285] During the hundred years following, the pearl reefs of Panama were not very productive, and relatively little attention was paid to them. The development of a market for the shells in the mother-of-pearl trade, about 1840, enhanced the profits of the few natives engaged in pearling in a desultory manner, and led to an increase in the number of fishermen. During some years when industrial and market conditions were favorable, large quantities of shells were exported. In 1855, for instance, 650 tons of these shells were shipped to England alone, and in 1859 the reported quantity was 957 tons. Those from the Island of San José, one of the Pearl Archipelago, were said to be the largest and choicest in the bay. Many of them were used in decorating the twin towers of the stately old cathedral at Panama.