After topping the flow charts every year since 2012, the world's biggest ETF manager has been forced to settle for second place so far in 2016.

As of May 31, Vanguard sat top with 2016 net inflows of $32.3 billion for its exchange-traded funds, ahead of BlackRock's iShares, the world's largest ETF manager, which registered gains of $27.1 billion, according to the data provider ETFGI.