Money managers began the new year by reducing wagers on rising oil prices to the lowest level in more than five years. Oil tumbled in the first days of 2016 as a global glut outweighed an increase in tension between Saudi Arabia and Iran. The decline accelerated as turmoil in China’s markets bolstered concern that an economic slowdown in the world’s biggest commodity-consuming nation is worsening. “The start of this year has been one of the worst of all time for multiple asset classes,” said Bob Yawger, director of the futures division at Mizuho Securities USA in New York. The rout is likely to extend into this week, he said.