Wall Street bond dealers cut their net high-yield bond holdings by 68 percent in the week ended Oct. 15 amid the biggest surge in volatility in more than a year.

The 22 primary dealers that trade with the Federal Reserve reduced their positions by about $4.3 billion to a net $2 billion, according to Fed data released Thursday. The debt lost 1.5 percent in the week ended Oct. 15 as concern mounted that a global slowdown would hamper U.S. central-bank efforts to stimulate economic growth.

The dealers, which include JPMorgan Chase & Co., Citigroup Inc. and Bank of America Corp., held a net $8 billion of high-yield bonds as recently as Sept. 24, Fed data show. Their current position is the lowest in data that goes back to April 2013, when the Fed changed the way it reported the information.