With general manager Jerry Dipoto acquiring three players via trades on Friday and also looking for room to protect prospects from the Rule 5 Draft, Wilhelmsen found himself as the odd-man out, though Dipoto indicated there was a chance he could be re-signed.
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"He had an interesting year and did a real good job for us, particularly in July," said Dipoto, who reacquired Wilhelmsen on June 22 after trading him to Texas in the offseason. "It was just a matter of once we made the trades today and added three players we felt we needed to protect, we were at 41. We needed to define an open spot."
The Mariners have young right-handers Edwin Diaz and Dan Altavilla returning in the bullpen, along with veterans Nick Vincent, Arquimedes Caminero, Steve Cishek and Evan Scribner.
"With Vincent, Caminero and Cishek being out of [Minor League] options or having service time that precludes options, we need some flexibility," Dipoto said. "That made the decision with what to do with Tom a little easier. He did a good job, and I wish him well in free agency. And this leaves something of an open door if something else arises and we want to bring him back."
Rollins, 26, went 1-2 with a 7.60 ERA in 31 games over the past two seasons after being acquired in the Rule 5 Draft from the Astros in 2015. The Texas native had a 7.71 ERA in 9 1/3 innings over 11 appearances during five stints with Seattle in 2016, while going 5-0 with a 3.77 ERA in 37 outings with Triple-A Tacoma.
Romero, who played in 94 games with the Mariners over the past three seasons, was granted his unconditional release to allow him to pursue an opportunity to play next year in Japan.
The 28-year-old out of Oregon State appeared in nine games over two stints with the Mariners last season, going 4-for-17 with a double and three RBIs. He hit .304 with 21 home runs and 85 RBIs in 106 games with Tacoma and was named to both the midseason and postseason Pacific Coast League All-Star teams.
Romero posted a .195/.242/.307 line with four homers and 17 RBIs in 215 at-bats over parts of the last three seasons with Seattle. His biggest opportunity came as a rookie in 2014, when he played in 72 games, but hit just .192 while playing mostly right field.
Romero was a 12th-round Draft pick in 2010.