A Morgan Stanley managing director, Brian Wornow, recently departed as head of the firm’s trading desk, but he is hardly alone among Wall Street traders who are weighing their options amid rapidly declining MBS production. According to Wall Street executives and lenders that feed their trading desks, there are other concerns about lower-than-expected bonuses this spring and an unwillingness on the part of some established firms to take risks in the mortgage market, particularly when it comes to new jumbo mortgages and other non-agency vehicles. Sources contend...