James Vernon, co-founder of Brevan Howard Asset Management, has stepped down as the group chief operating officer of the $20 billion hedge-fund firm, according to a person with knowledge of the matter.

Vernon, 51, remains a partner at the firm, the person said, asking not to be identified because the information is private. A spokesman for the firm declined to comment. Vernon was not immediately available to comment at his office in Jersey, the Channel Islands. HFMweek reported Vernon’s move earlier.

Brevan Howard, best-known for running hedge funds that bet on macroeconomic trends, has seen its assets slump from $40 billion in 2013 after two years of successive declines in its flagship product. The Brevan Howard Master Fund fell 0.3 percent in May, deepening its losses for the year to 2.1 percent, people said earlier this month. The money manager, run by billionaire Alan Howard, eliminated about 50 jobs in November, people said at the time.

Vernon helped create Brevan Howard in 2002 with four other traders from Credit Suisse Group AG’s proprietary fixed-income trading desk, including Howard. The first part of the firm’s name comes from the initials of founding partners Jean-Philippe Blochet, Chris Rokos, Vernon and Trifon Natsis.