Bill Ackman, CEO of Pershing Square Capital, speaks at the Wall Street Journal Digital Conference in Laguna Beach, California, U.S., October 17, 2017. REUTERS/Mike Blake/File Photo BOSTON, Sept 22 (Reuters) - Hedge fund manager William Ackman's 10% bet on Universal Music Group helped nearly double returns at his own portfolio to 15.3% this week after shares in the world's biggest music label surged in their first hours as a publicly traded company. Ackman, who runs hedge fund firm Pershing Square Capital Management, told investors that his Pershing Square Holdings portfolio returned 15.3% after fees since January.