BI Whale Watch: 9 stocks that investing legends like Warren Buffett are betting at least 20% of their portfolios on

• Warren Buffett is stepping down as CEO of Berkshire Hathaway by year-end.
• Buffett is betting most of his portfolio on Apple.
• High concentration in stocks can drive performance but can pose outsized downside risk.

Warren Buffett, perhaps the greatest investor of all time, announced on Saturday that he would step down as CEO of Berkshire Hathaway at the end of the year.

Given the occasion, we thought it would be a good opportunity to update our BI Whale Watch series, which periodically takes a look at some of the huge wagers that investing legends like Buffett are making.

Our list this time includes nine stocks that famed investors are betting at least 20% of their portfolios on, according to GuruFocus data on 144 top investors. How those positions have shifted since our last installment in February, if applicable, is also included.

There are a few notable changes to the list this time around. One is that Seth Klarman, CEO of Baupost Group, has dropped off our list. His bet on Liberty Global (LBTYK) has fallen from a 26% weighting to 15% over the last few months. Fairfax Financial CEO Prem Watsa's positions in Occidental Petroleum and Orla Mining have also shrunk below the 20% marker.

High concentration levels drive performance for some investors who like to load up on high-conviction picks. Buffett's longtime partner Charlie Munger, for example, was a proponent of the method.

"I think it can be a rational choice, in some situations, for a family or a foundation to remain 90 percent concentrated in one equity," he wrote in his book, "Poor Charlie's Alamanac."

But the strategy can be risky if the bet doesn't work out.

The nine stocks are listed below in ascending order of their weight in the investors' respective portfolios.