Wes Edens, a co-owner of the Milwaukee Bucks, has shot his share of air balls at his private-equity firm Fortress Investment Group. With mortgage assets, Edens has found his mark.

Shares of the mortgage real estate investment trust that Fortress manages soared 50 percent, including dividends, in the past year. The REIT, New Residential Investment Corp., alone accounts for more than a quarter of all of Fortress’ private-equity fees.