Viad Corp. announced Monday that John Jastrem, president of its GES business unit, is retiring. Paul Dykstra, Viad's chairman, president and CEO, will assume Jastrem's role while a search for a successor is conducted. Dykstra has plenty of experience in the exhibition industry: He served as president and CEO of GES from 2000 to 2006 before being named president and chief executive officer of the parent company.