This month, several managers were hit by a new wave of redemptions, which came on top of an initial round of withdrawals this year, people aware of the matter said.
"It was our Black Monday," said one fund manager, referring to the large number of assets withdrawn by Saudi Arabia last week.
Institutions benefited from years of rising assets under management from oil-rich Gulf states, but are now feeling the pinch after oil prices collapsed last year.
Nigel Sillitoe, chief executive of financial services market intelligence company Insight Discovery, said fund managers estimate that Sama has pulled out $50 billion-$70 billion over the past six months.
"The big question is when will they come back, because managers have been really quite reliant on Sama for business in recent years," he said.
Since the third quarter of 2014, Sama's reserves held in foreign securities have declined by $71 billion, accounting for almost all of the $72.8 billion reduction in overall overseas assets.
Other industry executives estimate that Sama has withdrawn even more than $70 billion from existing managers.
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While some of this cash has been used to fund the deficit, these executives say the central bank is also seeking to reinvest into less risky, more liquid products.
"They are not comfortable with their exposure to global equities," said another manager.
Fund managers with strong ties to Gulf sovereign wealth funds, such as BlackRock, Franklin Templeton and Legal & General, have received redemption notices, according to people aware of the matter.
Some fund managers have seen several billions of dollars of withdrawals, or the equivalent of a fifth to a quarter of their Saudi assets under management, the people aware of the matter said.
Institutions such as State Street, Northern Trust and BNY Mellon have large amount of assets under management and are therefore also likely to have been hit hard by the Gulf governments' cash grab, the people added.
"We are not that surprised," said another fund manager. "Sama has been on high risk for a while and we were prepared for this."
Sama has over the years built up a broad range of institutions handling its funds, including other names such as Aberdeen Asset Management, Fidelity, Invesco and Goldman Sachs.
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BlackRock, which bankers describe as the manager handling the largest amount of Gulf funds, has already reported net outflows from Europe, the Middle East and Africa.
Its second-quarter financial results reported a net outflow of $24.1 billion from Emea, as opposed to an inflow of $17.7 billion in the first quarter.
Market participants say the outflow is in part explained by redemptions from Saudi Arabia and other Gulf sovereign funds, such as Abu Dhabi.
BlackRock and other funds declined to comment or did not respond to requests for comment. Sama did not respond to request for comment.