Eric Langille, senior managing director and co-head of New York credit derivatives trading at Bear Stearns, has left the firm. It could not be determined whether Langille, who could not be reached, has joined a competitor. Martin St. Pierre, senior managing director and co-head of New York credit derivatives trading alongside Langille, was traveling and could not be reached. Michele Agostinho, spokeswoman at Bear Stearns in New York, declined comment.