Saunders was optioned to Tacoma on Thursday and will begin the season on the club for which he batted .310 with 13 home runs and 32 RBIs in 248 at-bats last year before being called up to the Mariners on July 25. Right-handed relievers Mike Koplove and Levale Speigner were re-assigned to Minor League camp, completing the morning's transactions.
Saunders, who is viewed as one of the team's better prospects, showed athleticism in left field and on the basepaths while with Seattle, but he hit .221 in 122 at-bats and showed the club that he needed more seasoning.
"I like what he did at the end of last year," manager Don Wakamatsu said of Saunders. "We had a long discussion today. We're still extremely high on him.
"We like the current path he's on now. He needs to refine his lower half and have more efficiency on pitches. We like what we see with his maturity."
The only problem for Saunders is that the Mariners invested in more mature players in the offseason,
General manager Jack Zduriencik traded for Milton Bradley, who figures to get the majority of the time in left field, and then signed free agent Eric Byrnes, who can back up all three outfield positions or start against left-handers when Bradley relieves Ken Griffey Jr. at designated hitter.
"[Saunders] was not going to get a lot of playing time," Wakamatsu said. "But where he's at and with his age, it's important to have him playing."
The roster move leaves the Mariners with 41 players in Major League camp, including 31 roster players and 10 non-roster invitees.
Doug Miller is a national writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.