The long-awaited decline in U.S. oil output has begun, data show, but many investors and analysts are still waiting for prices to stage a sustained recovery. The rapid growth in America’s production over the past several years was a major driver behind the plunge in the benchmark U.S. oil price, which is down 53% from a year ago. “We now know that the U.S. [production] is in decline,” said Eric Nuttall, portfolio manager at Sprott Asset Management, which manages about $5.8 billion.