Seattle Mariners Top 20 Prospects: #20 Jonathan Aro

Jul 1, 2015; Toronto, Ontario, CAN; Boston Red Sox relief pitcher Jonathan Aro (65) delivers a pitch against Toronto Blue Jays at Rogers Centre. Mandatory Credit: Dan Hamilton-USA TODAY Sports
Jul 1, 2015; Toronto, Ontario, CAN; Boston Red Sox relief pitcher Jonathan Aro (65) delivers a pitch against Toronto Blue Jays at Rogers Centre. Mandatory Credit: Dan Hamilton-USA TODAY Sports /

It remains to be seen whether Jonathan Aro can do enough this spring to make the club, but there is little doubt he will toe the rubber at Safeco Field in 2016.

The Seattle Mariners acquired Jonathan Aro and Wade Miley from the Boston Red Sox this past December in exchange for Carson Smith and Roenis Elias. Aro was obviously the least notable player involved, but he has a chance to make a significant impact with the M’s in 2016.

Originally signed as an international free agent in 2011, Aro steadily climbed through the Red Sox’s minor league system before making his debut last June. He struggled in his first taste of the big leagues, going 0-1 and posting a 6.97 ERA across 6 appearances. Aro struck out 8 and walked 4 through 10.1 innings of work.

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Aro disappointed during his brief stint in Boston last season, but he has found success at every level in the minor-leagues. He began his professional career as a 20-year-old in 2011 with the Red Sox affiliate in the Dominican League. Aro went 2-2 with a 3.06 ERA in 9 outings. He registered a remarkable 9.50 strikeout to walk ratio across 47 innings of work.

The Sox opted to send Aro to their affiliate in the Gulf Coast League in 2012. He went 3-4 with a 4.66 ERA in 11 appearances. Aro struck out 34 and walked 9 across 38.2 innings. This was his toughest season as a pro, but Aro used the experience as a learning experience.

Aro spent the entire 2013 working out of the Lowell Spinners bullpen, and he excelled. The right-hander went 5-3 with a 2.14 ERA across 15 appearances in the New York-Pennsylvania League. Aro struck out 49 and walked 12 over the course of 54.2 innings pitched.

The Dominican Republic native exploded onto the scene in 2014, proving to be one of the most dominant hurlers in the Red Sox system. Aro began the season with the Greenville Drive before being promoted to Boston’s High-A affiliate in Salem, VA. He combined to post a record of 3-3 and an ERA of 2.17 in 32 games. Aro racked up 98 punch outs, issued 29 free passes and allowed just 1.069 walks/hits per inning.

Aro was on the fast track to Boston following his impressive 2014 season. He pitched at three different levels in 2015, including the Major Leagues. Aro went 3-2 with a 2.82 ERA in 8 games with the Portland Sea Dogs before earning a promotion to the Pawtucket Red Sox. Aro continued to pitch effectively, posting a 3.14 ERA across 51.2 innings in the International League.

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As with many young pitchers, Jonathan Aro relies heavily on his fastball. Aro’s heater hovers in the 92 mph range, and he used it 71% of the time last season in Boston. He also mixes in an improving circle change. His slider has a chance to develop into a solid out pitch in the near future.

Baseball Reference and FanGraphs are optimistic about Aro in 2016. Baseball Reference predicts he will go 2-2 with a 4.20 ERA and 1 save across 30 innings with the Mariners. The mathematicians over at FanGraphs anticipate Aro will go 1-2 with a 3.93 ERA in his debut season in the Emerald City.

The 25-year-old right-hander is one of the few Mariners prospects who has a real shot to crack the opening day roster. The M’s bullpen is full of question marks right now, as there appear to be multiple jobs up for grabs. Aro is on Seattle’s 40-man roster, and should get plenty of opportunities to prove himself this spring in Peoria with the big club.

Next: Seattle Mariners Season Preview: Seth Smith

Jerry Dipoto has said in the past that controlling the strike zone will be a top priority for the Mariners this season. That is something Aro is very adept at doing. During his minor-league career, Aro has posted a 4.04 strikeout to walk ratio. That is an impressive figure, and it suggests he will be a dependable arm for years to come in the M’s bullpen.