US - Sally Choi, general manager of the 43,000-member Los Angeles City Employees' Retirement System, will leave October. 15 to "pursue other opportunities", the fund said.
The $9bn pension plan for the city's civilian employees, known as Lacers, lost $700m, or 5.7%, in the quarter ending in June compared with the preceding period, bringing its one-year return to 12.9%.
The retirement system's board, which appointed Choi in July 2008, will consider an interim replacement at its next meeting.
The nation's second-largest city by population is considering changes in its pension plans that may increase contribution rates and reduce benefits for new hires, City Administrative Officer Miguel Santana said in an interview on October 7. The cost of city employee pensions is expected to double to $1.6bn by 2015, he said.
"Sally Choi has effectively led Lacers through a number of diverse and challenging issues -- many of which could not have been anticipated," Roberta Conroy, president of the board, said. "Her experience and integrity will be missed."
The Pensions and Lifetime Savings Association (PLSA) has announced it will shrink its board by more than one-third as part of a governance overhaul to make it "agile and more appropriate".
Smaller FTSE 350 defined benefit (DB) schemes were nearly 15 percentage points less well-funded than larger schemes in 2017, according to a Goldman Sachs Asset Management (GSAM) analysis.
The advent of collective pension systems could help the UK avoid demographic challenges which will make it "impossible" for society to help savers in retirement, experts say.