TAMPA — Free agency began with an ending as seven-time Pro Bowl guard Logan Mankins informed the Bucs he was retiring Monday. Though not a surprise, the team began the process of trying to acquire more veteran linemen to protect franchise quarterback Jameis Winston.Meanwhile, Seahawks guard J.R. Sweezy also got attention from the Bucs and Jaguars. Sweezy, 26, has started at least 15 games the past three seasons for Seattle, the majority at right guard.The Bucs have $57.4 million in salary cap space, fourth-most in the NFL. The two-day legal tampering period of free agency began Monday. Teams cannot sign free agents until 4 p.m. Wednesday, the start of the new league year.Bucs free agent running back Doug Martin reportedly has received interest from at least half a dozen teams. The Jaguars, Broncos, Raiders and 49ers are all in the running back market and could have an interest in the NFL's second-leading rusher of 2015. Denver placed a low tender on restricted free agent running back C.J. Anderson, giving it only right of first refusal.As perhaps a preemptive strike Monday, the Bucs expressed interest in Jets free agent Chris Ivory if Martin signs elsewhere. Dolphins running back Lamar Miller also is expected to be a Bucs target should they lose Martin, who rushed for 1,402 yards and six touchdowns last season.Much like the Broncos did with Peyton Manning, the Bucs wanted to give Mankins, who turns 34 on Thursday, as much time as possible to be certain of his decision. But unlike Manning, don't expect Mankins to have a news conference. He always has been a humble player who didn't seek the spotlight.Mankins started 31 of 32 games since being traded from the Patriots in 2014 for tight end Tim Wright and a 2015 fourth-round draft pick. He was a big reason why Tampa Bay had the league's fifth-best offense last season. But having struggled all season with a knee injury, he decided to call it quits after playing his final game in the Pro Bowl."It's always difficult losing a player of Logan's caliber both on the field and in the locker room," Bucs general manager Jason Licht said. "He's one of the toughest, most intelligent and skilled players at his position that I have seen in my years around this game. Logan distinguished himself as the ultimate professional over his 11-year career and he was an unquestioned leader for us over the last two seasons. His leadership, work ethic and selflessness played a key role in the development of our younger players and he set the standard which we use to evaluate all of our offensive linemen."The Bucs' plan right now would be to replace Mankins at left guard with either third-year pro Kevin Pamphile, who started one game there a year ago, or center/guard Evan Smith. But the team began the process of finding help in free agency.A first-round draft selection in 2005, Mankins spent his first nine seasons with New England and was its most consistent offensive lineman. His trade was the result of a contract dispute and he missed out on the Pats' win in Super Bowl XLIX in 2014.The Bucs also are expected to re-sign safety Keith Tandy, an unrestricted free agent.Times staff writer Greg Auman contributed to this report.