April 30 (Reuters) - The value of derivative-related

margin calls at hedge funds and other market participants nearly

tripled after the Trump administration announced

larger-than-expected U.S. tariffs this month, before declining

after a 90-day pause, according to OSTTRA, which provides

post-trade services.

Data showed the total value of those calls rose by 180% from

April 2-10, placing significant liquidity stress on investors,

and raising the number of disputes between trading parties by

25%, it said.

Margin call values have now returned to pre-tariff levels,

said OSTTRA, which KKR said this month it would buy from

S&P Global ( SPGI ) and CME Group ( CME ).

The demand for margin calls increased 35%, much of which

stemmed from variation margin, or additional collateral

investors must pay to reflect the change in market value of

their position to prevent them from defaulting on a trade,

OSTTRA said.

OSTTRA, which runs a platform that reconciles more than 90%

of bilateral derivatives globally, collects data by tracking

post-trade processes, focusing on margin calls, collateral

movements, and disputes across global financial markets.

The margin calls data is drawn primarily from the derivatives

market, specifically focusing on exchange-traded derivatives and

cleared repurchase agreement trades.

Hedge funds typically use margin accounts to borrow cash

from prime brokers to trade.

To show how heightened volatility resulting from tariff

policies has been costly for market participants, OSTTRA said a

hedge fund managing 100 margin calls per day averaging $5

million per call would normally face $500 million in daily

collateral flows.

But the recent volatility meant that fund suddenly had an

additional $900 million in collateral demands, bringing its

total daily margin obligations to $1.4 billion, much of which

may require funding in cash, it added.

The margin call demand was seen across markets, according to

OSTTRA, including equities, rates, foreign exchange, commodities

as well as credit derivatives and repurchase agreements.

"The frequency and size of margin calls did go up during

this episode," said Ted Post, head of Prime Sales Americas at

BNP Paribas. "The amount of margin calls were elevated and

that's certainly a sign of stress in markets, but hedge funds

managed well through the event."

Post added the risk was mitigated because many equity

derivatives desks on Wall Street were positioned and hedged for

this, as were their clients.