Assets under management (AUM) at the worlds 20 largest pension funds fell last year for the first time since 2012, research from the Thinking Ahead Institute has found.
The top 20 funds' AUM declined by 1.6% in 2018, according to the findings, while assets at the 300 largest funds fell by 0.4% to $18trn (£14.9trn), compared with a 15.1% rise in 2017.
This means that 40.7% of total assets are now managed by the 20 largest funds, down from 41.1% last year.
However, the world's 20 largest funds' AUM growth rate of 4.7% between 2013 and 2018 remained higher than the 3.9% recorded by all pension funds in the index.
"A tougher market environment meant AUM growth paused, but the underlying trend remains one of growing pension markets," Thinking Ahead Group head of research, Bob Collie, said.
"Many of the most important developments start with the largest funds, and as new investment ideas gain traction in these organisations, they influence the whole market."
The US continues to have the largest number of funds in the top 300 ranking with 141, followed by the UK on 24, Canada on 17, Australia 16 and Japan 15.
The top five largest pension funds by AUM ($millions) are shown below:
The findings also show that defined contribution (DC) assets increased by 5.1% among the top 300 funds in 2018, with defined benefit (DB) assets declining by 0.2%.
On a weighted average for the top 20 pension funds, a total of 44.5% of assets are invested in equities, with 37.2% in fixed income and 18.3% in alternatives and cash.
Sovereign and public sector pension funds account for 68.5% of total AUM. Sovereign pension funds represent $5.1trn, while sovereign wealth funds account for $7.9trn.
"The pace of change in the investment world is a challenge, and scale is a huge advantage in a lot of ways," Collie continued.
"It's particularly notable that a majority of the largest funds are now highlighting the importance of sustainability. There's also an evolving recognition of the role large investors play within society, and the responsibility that comes with it."