The world's largest retirement funds saw their assets dip 0.4% in 2018, to $18 trillion.
That compares with an increase of 15.1% the prior year, according to the latest survey by Pensions & Investments and the Thinking Ahead Institute of the world's 300 largest retirement plans.
For the 20 largest retirement funds, assets fell 1.6% to $7.3 trillion, vs. a nearly 17% rise in 2017.
Bob Collie, London-based head of research for the Thinking Ahead Group, the institute's executive team, said the drop reflected weak short-term returns.
Global equity markets, as measured by the MSCI All Country World index, produced a 9.42% loss in 2018.
"The (financial) market wasn't as strong in 2018, but investors on the whole would still expect total AUM to be increasing over time" as participants' savings are growing, Mr. Collie said.
"Obviously defined benefit is peaking at some point. That has probably happened in North America but is yet to happen in the U.K. and other markets around the world. There will be a point when DB will go away but that (gap) will more than be made up for by DC increases."
"We have growing retirement savings' markets underlying the overall picture from year to year,'' even if the value of assets fluctuates, he added.
Mr. Collie said the 300 largest asset owners have a lot at stake when it comes to geopolitical events such as trade wars. The current dispute between U.S. and China, for example, could reverse the 20-year trend toward greater integration of the two countries' markets and economies, he said.
In 2018, the top 300 funds accounted for about 44.9% of total global retirement assets as of Dec. 31, up from 43.6% at year-end 2017.
Mr. Collie said there are still many plans that don't have the scale to become a top-tier organization. Retirement plans have to think about achieving that scale, which could include merging with other asset owners, he said.
"The pendulum is swinging to fewer organizations," partly because of technological advances and partly because of the strong focus on costs, he added.
Due to having to compete for assets with large sovereign wealth funds, "it's getting expensive for (plans) to build a leading organization," he said.