Executive Director Tom Spencer in an email said fund trustees voted to put the firm on its watchlist after it learned that Libby Toudouze, one of Cushing's partners and portfolio managers, had left the firm to pursue other opportunities.
The decision was made at a Jan. 23 meeting of the board of trustees.
Cushing manages a $352.1 million master limited partnership portfolio that is invested in energy-related infrastructure, Mr. Spencer said.
Mr. Spencer described the move as "a standard action when a significant officer and portfolio manager leaves a firm," and added that Cushing's "status will be reviewed on a regular basis."
Mr. Spencer said the fund had $15.9 billion in assets as of Dec. 31 and posted a return of 5.28% for 2018, according to an investment performance report that consultant AndCo Consulting presented at the board meeting.