By David Randall and Carolina Mandl

NEW YORK (Reuters) -Fund managers zeroed in on the U.S. financial sector during the first quarter, a period marked by the worst banking crisis since 2008.

The S&P Regional Banking Index fell approximately 25% during the quarter as a run on deposits sank Silicon Valley Bank and Signature Bank in March, both of which were at the time the largest banking failures since the Great Financial Crisis. The S&P Regional Banking index is now down 36% for the year to date.

Billionaire investor Jim Simons' Renaissance Technologies LLC, which has more than $100 billion in assets under management, bought approximately 7.1 million shares of embattled First Republic Bank during the quarter and still held them as of March 31, when they closed at $13.99 per share, according to securities filings released Monday. The firm collapsed on May 1 in what was the largest bank failure since 2008.

The securities fillings did not show whether the firm sold any of its position before the firm's May 1 seizure by regulators.

Famed "Big Short" investor Michael Burry's Scion Asset Management, meanwhile, added a number of new positions in regional banks, including stakes in First Republic, PacWest and Western Alliance Bancorp.

Boston-based Adage Capital Partners added a new position of approximately 185,000 shares of First Republic during the quarter, while New York-based Alpine Global Management LP added a new position of approximately 1.7 million shares, filings showed.

Renaissance Technologies, Adage Capital, Alpine Global, and Scion did not respond to requests to comment.

The positions were revealed in quarterly securities fillings known as 13-fs. While backward looking, these snapshots show what funds owned on the last day of the quarter and are one of the few ways that hedge funds and other institutional investors have to declare their positions. They may not reflect current holdings.

Among prominent sellers of First Republic’s stock was Ray Dalio's Bridgewater Associates, one of the world's largest hedge funds, which closed its position amid a broad portfolio shift away from financial firms.

The fund liquidated its positions in big U.S. banks including Bank of America Corp, Goldman Sachs Group Inc, and Morgan Stanley, and slashed its positions in smaller banks such as Bank of Hawaii Corp, PacWest, PNC Financial Services Group, Citizens Financial Group and Capital One Financial Corp.

London-based Marshall Wace sold 51,300 shares of First Republic in the first quarter, closing its position in the bank.

Berkshire Hathaway, the conglomerate run by billionaire Warren Buffett, added a new position in Capital One Financial while dissolving its positions in US Bancorp and Bank of New York Mellon Corp, filings showed.

(Reporting by David Randall; Editing by Ira Iosebashvili, Marguerita Choy and Lisa Shumaker)