South Korean credit card companies saw their earnings tumble in the first quarter of this year, mainly due to a decrease in gains from their investment in stocks, the financial regulator said Tuesday. The combined net profit of seven stand-alone credit card firms reached 462.2 billion won (US$412.3 million) in the January-March period, down 45.2 percent from 843.1 billion won the previous year, according to the Financial Supervisory Service (FSS).