Also reassigned to Minor League camp were four non-roster invitees: outfielder Mike Wilson, and pitchers Royce Ring, Denny Bautista and Justin Miller.
Tuiasosopo had one option remaining, so this is the last year he can be sent to the Minor Leagues without being exposed to waivers. The option lasts all year, so Tuiasosopo can be moved between Tacoma and Seattle throughout the season without being waived.
Tuiasosopo, 24, hit .300 with one home run and eight RBIs in 40 at-bats this spring. The 2004 third-round Draft pick has spent parts of the past three seasons with Seattle in limited roles, hitting .176 in 193 at-bats, but the club feels he needs consistent playing time in order to develop.
2010 Spring Training - null
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That leaves 30 healthy bodies competing for spots on the final 25-man roster, which must be finalized by Thursday morning.
The moves with Ring, Bautista and Miller leave the club with 14 healthy pitchers in camp, including eight relievers. The Mariners likely will break camp with seven relievers from among the group of David Pauley, Brandon League, Chris Ray, Jamey Wright, Josh Lueke, Tom Wilhelmsen, Aaron Laffey and Cesar Jimenez.
Ring, who pitched briefly for the Yankees last year, was sent down despite a strong spring, with a 2.25 ERA in eight appearances. Manager Eric Wedge said that the decision came down to needing more versatility.
"We wanted to make sure we had guys who were going to give us a little more length, multiple-inning guys," Wedge said. "He's more of a left-on-left guy. You never know how your bullpen is going to play out, but we'll see what he's going to do. There are some tough decisions to be made. We made some tough ones today and will continue to do that in the next couple of days."
Tuiasosopo's departure leaves the club with eight infielders, including Mangini. Veteran non-roster invitee Adam Kennedy clearly has won the utility infield role. Ichiro Suzuki, Milton Bradley, Ryan Langerhans, Michael Saunders and Gutierrez are the remaining outfielders.
Catcher Chris Gimenez could also factor into the outfield mix as a "super utility" candidate, given his background as a converted outfielder who can also play first and third.
It's uncertain what lies ahead for Gutierrez. It's increasingly likely he'll begin the season on the DL, given he's played just nine games this spring and has now missed the past nine.