Substantial development in the pearling industry around the Qatari Peninsula occurred during the Abbasid era. Slave labour was used in the nearby mainland pearling industry. Traditional Qatari folk music is primarily centered on pearling. British maritime policing meant that pearling fleets could operate in relative security. Present day natural pearling is confined mostly to seas off Bahrain. Several other outback industries, notably pearling, also employed Aboriginal workers. The Japanese invention of cultured pearls also contributed to the collapse of Kuwait's pearling industry. Approximately 100 Aboriginals assisting survivors and 307 men from the pearling fleet were drowned. According to a source about pearling, the Persian Gulf was the best location for pearls. Ibn Battuta also noted the great wealth of the area thanks to the pearling industry. In 1858 he added equipment for pearling barley. The main centers of pearling extended from Bida (Doha) to Dubai. Future plans were to heavily reflect on the city's historic pearling tradition. The Gulf of Mexico was also known for pearling. It may be polished, a process known as "pearling".