(Bloomberg) -- Mary Anne Wiley left her position as managing director and head of iShares Canada, the exchange- traded funds unit of BlackRock Inc., as competitors encroach on the company’s leading market share.

Wiley told management earlier this year she planned to leave and departed the company last week, said Maeve Hannigan, a spokeswoman for iShares Canada. Warren Collier, chief operating officer for U.S. iShares, is replacing Wiley as acting head while the firm seeks a successor, Hannigan said in an interview today.

Wiley took up the job in January 2012 after BlackRock acquired then-competitor Claymore Investments Inc. from Guggenheim Partners LLC. The two businesses, then the top two providers in the country, accounted for about 83% market share at the time.

A phone message left with Wiley wasn’t immediately returned.

IShares Canada remains the largest ETF provider in the country with C$43.8 billion ($40.5 billion) in assets and a 64% market share as of May 31, down from 67% at the end of 2013, according to data from the Canadian ETF Association. BlackRock is the world’s largest money manager, overseeing about $4.4 trillion in assets.

Mounting Competition

The firm faces increasing competition in the Canadian market amid an environment of falling fees. Bank of Montreal’s ETF unit, the No. 2 provider in Canada, has seen its market share rise to 22% from 20% at the beginning of the year, while its asset values have jumped 17%.

Rajiv Silgardo, co-chief executive officer at BMO Asset Management Inc., said in a June 17 interview that his firm’s ETF business will double its assets in the next five years as lower fees draw investors.

In March, iShares cut fees on some of its most popular ETFs, including the iShares S&P/TSX Capped Composite Index ETF, the fifth-largest ETF in Canada by assets at about C$1.59 billion, to 0.05% from 0.25%.

Recent low-cost entrants, Vanguard Investments Canada Inc. and Purpose Investments Inc., founded by Claymore founder Som Seif, have further fractured the market.

“We would like to thank Mary Anne for her strong leadership of iShares Canada and her tremendous contributions to BlackRock,” Noel Archard, managing director and head of BlackRock Canada, said in a statement sent to Bloomberg.

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