As Gulfstream Park enters into its self-proclaimed "new era in racing," it will be doing so without one of the key members of its management team.39-year-old Mike Tanner, the track's director of marketing and a 12-year employee, announced he will be leaving Gulfstream at the end of September. Tanner has been named by Harrah's Corporation to run Chester Downs, a new harness track outside of Philadelphia that is expected to be operational next June."I've loved my time at Gulfstream but this was an opportunity that I couldn't pass up," said Tanner. A native of southern New Jersey, Tanner added that the new job would allow him to "go back home."Tanner joined Gulfstream in 1993, serving for eight years as the assistant director of communications under Joe Tanenbaum. He added oversight of Gulfstream's simulcasting operations to his responsibilities in 2001, and served a year as a special assistant to the president before replacing Dave Rovine as head of marketing last year.Gulfstream President Scott Savin said that Tanner's position would not be filled. Instead, he indicated that he will handle the marketing duties himself while hiring an individual to oversee the media functions. Mike Mullaney, Tanner's assistant, is expected to be named to the latter position."Mike (Tanner) was an integral part of the management team here and will obviously be a loss," Savin said. "But the fact that an organization like Harrah's has seen fit to offer him a position of such responsibility reflects well on what we've been able to accomplish at Gulfstream."Gulfstream is in the midst of a massive redevelopment project that will transform the 65-year-old Hallandale Beach, Fla. racetrack into a shopping and entertainment center, featuring clubs, restaurants, a mall, concert venues, and slot machines.