NEW YORK ( TheStreet) -- The National Stock Exchange's new report on ETF flow data for May provides a wealth of information on investor preferences.

Overall, May was a trying month for investors. As the global marketplace ran into turmoil, investor interest in exchange-traded funds waned. For the first time in 2011, the industry saw net outflows. The $777 million in net outflows marked a dramatic shift from April, when there were $20 billion in inflows.

Industry leaders including State Street ( SST), PowerShares, and BlackRock ( BLK) witnessed the most staggering outflows, totaling $5.98 billion, $2.16 billion and $1.95 billion respectively. Smaller fund providers such as ETF Securities and Guggenheim ran into notable headwinds as well.

Much of these ETF goliaths' outflows can be attributed to general investor disinterest in veteran broad index-based ETFs. SPDR S&P 500 ETF ( SPY), PowerShares QQQ ( QQQ), and iShares Russell 2000 Index Fund ( IWM) led the industry with outflows in May, with $4.91 billion, $2.54 billion, and $2.06 turning to the exits respectively.

Many of the largest physically-based precious metal ETFs were shunned as well. As volatility perked across the commodities spectrum, investors fled funds such as iShares Silver Trust ( SLV) and SPDR Gold Trust ( GLD).

Interestingly, there was one physically-based fund from the precious metals realm that proved popular in May. The iShares Gold Trust ( IAU) ended the month with net inflows totaling $165 million. As in recent months, investor preference for IAU over GLD can likely be traced to the iShares product's reduced expense ratio.

Although the industry as a whole witnessed net outflows during May, it is important to note that not all fund providers closed out the month in the red. On the contrary, Vanguard and Van Eck managed to buck the trend, gathering up $7.05 billion and $985 million respectively.

Much of Van Eck's gains in May can be traced to a single fund, the Market Vectors Agribusiness ETF ( MOO). During the month, this fund topped the list of inflow recipients, gathering nearly $1.50 billion as investors clamored for agriculture-related equities. Interestingly, the same could not be said for futures-based agriculture ETFs. The PowerShares DB Agriculture ETF ( DBA) ended the month with $374 million in outflows, placing it among the 10 largest decliners.

Vanguard funds dominated the ranks of major inflow recipients, accounting for five of the top 10 positions. Among the products that saw the most popularity were the Vanguard MSCI MidCap ETF ( VO), Vanguard MSCI Small Cap ETF ( VB), Vanguard MSCI Small Cap Growth ETF ( VBK), and Vanguard MSCI Emerging Market ETF ( VWO).

Many of the industry's biggest asset gainers were defense-focused, including the Consumer Staples Select Sector SPDR ( XLP), Healthcare Select Sector SPDR ( XLV), iShares Barclays 20+ Year Treasury Index Fund ( TLT) and PowerShares DB U.S. Dollar Index Bullish ( UUP) saw heavy inflows as investors sought protection from the market's volatility.

Meanwhile, more aggressive asset classes were avoided. The SPDR S&P Metals & Mining ETF ( XME), Energy Select Sector SPDR ( XLE) and SPDR KBW Bank ETF ( KBE) saw heavy outflows.

The same could be said for commodity-related international funds. Market Vectors Russia ETF ( RSX) and iShares MSCI Canada Index Fund ( EWC) saw $496 million and $321 million exit. China proved unpopular as well: the iShares FTSE China 25 Index Fund ( FXI) saw $679 million in outflows.

May's ETF flow data properly reflected the cautious and jittery market atmosphere that embodied this trying month. In the event that the market's soft spot persists as we close out the first half of 2011, many of the same themes that we witnessed during May will likely remain in play.

Written by Don Dion in Williamstown, Mass.

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At the time of publication, Dion Money Management owned PowerShares QQQ, iShares Gold Trust, iShares Barclays 20+ Year Treasury Index Fund, PowerShares DB U.S. Dollar Index Bullish and iShares MSCI Canada Index.