Soros Fund Management LLC lowered its investment in the SPDR Gold Trust, the biggest such fund, by 12 percent to 530,900 shares as of March 31, compared with three months earlier, a Securities and Exchange Commission filing showed yesterday. Funds run by Northern Trust and BlackRock showed reductions of more than half, according to earlier filings. Paulson & Co., the largest investor in SPDR, held 21.8 million shares, while Schroder Investment Management Group bought 2.1 million.