Seattle Mariners Promote Several Interesting Pitching Prospects

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Many minor league players within the Seattle Mariners farm system will take the next steps in their respective careers.
The Mariners promoted a pair of top 100 prospects, switch-pitcher Jurrangelo Cijntje and shortstop Colt Emerson, from the High-A Everett AquaSox to the Double-A Arkansas Travelers on Sunday. The organization announced another set of players moving up the farm system Monday.
Right-handed pitcher Stefan Raeth was promoted to the Travelers; right-handed pitcher Pedro da Costa Lemos and left-handed pitcher Calvin Schapira were promoted to the AquaSox; and right-handed pitchers Jose Romero and Gleiner Diaz were moved up to the Single-A Modesto Nuts.
Modesto is getting a few new arms. #TridentsUp
— Mariners Player Development (@MsPlayerDev) August 4, 2025
🔹 RHP Jose Romero (@ModestoNuts)
🔹 RHP Gleiner Diaz (@ModestoNuts) pic.twitter.com/xgG8Dx9B4V
The 24-year-old Raeth has posted a 2.45 ERA with 45 strikeouts in 40.1 innings pitched across 32 appearances this season.
Perfect 8th inning for Stefan Raeth. pic.twitter.com/2QcA0ZknQb
— Mariners Minors (@MiLBMariners) July 30, 2025
The 22-year old Costa Lemos had a 3.68 ERA with 59 strikeouts in 51.1 innings pitched across 26 outings.
The 25-year-old Schapira has a 2.18 ERA and has fanned 22 batters in 20.2 innings across 17 appearances.
Romero, 21-years-old, has a 3.79 ERA and has struck out 46 batters in 54.2 innings across 13 outings (nine starts).
Diaz, who's also 21-years-old, has posted a 7.96 ERA with 36 strikeouts in 31.2 innings across 23 outings.
Gleiner Diaz strikes out 3 in a scoreless first Northwest League inning. pic.twitter.com/3wEh27CpMG
— Mariners Minors (@MiLBMariners) August 4, 2024
Seattle has one of the best farm systems in the league according to several publications. MLB Pipeline has eight Mariners prospects ranked in the top 100 and Baseball America also ranks eight prospects in its own respective top 100.
Seattle also has depth in its farm system beyond its top 100 prospects. Players not in the top 100 like Ben Williamson, Rhylan Thomas and Logan Evans have all received playing time with the team this season and weren't in the top 100 going into the season, and there's a chance that these crop of pitchers make an impact on the major league club in the future.
Related Minor League Baseball stories
MARINERS PROMOTE PAIR OF TOP 100 PROSPECTS TO DOUBLE-A: Switch-pitcher Jurrangelo Cijntje and shortstop Colt Emerson will be reporting to the Arkansas Travelers. CLICK HERE
TOP 100 MARINERS PROSPECT REACHES NEW CAREER-HIGH: Switch-pitcher Jurrangelo Cijntje was dealing in a start for the Everett AquaSox on Saturday. CLICK HERE
MARINERS STARTING PITCHER DOMINATES IN REHAB START WITH TACOMA: Bryce Miller looked in near-top form in a rehab outing with the Tacoma Rainiers on Friday. CLICK HERE
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Teren Kowatsch is a staff writer for ''Minor League Baseball on SI'' and other "On SI'' baseball sites. He has been a writer for “On SI’’ for two years and is a graduate of the University of Idaho. You can follow him on Twitter @Teren_Kowatsch