Bass was expected to be part of the Mariners' bullpen mix next season, but he has asked to pursue an opportunity in Japan. The move opens up a spot on Seattle's 40-man roster, which now stands at 39.
Bass posted a 4.50 ERA in 33 relief outings with the Rangers last season and is 5-9 with a 4.50 ERA in 129 games, including 18 starts, over five seasons in the Majors with the Padres, Astros and Rangers.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB, read his Mariners Musings blog, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.