Stock Up, Stock Down for Seattle Mariners' Top 10 Prospects for Week 7

For the first time in several years, the Seattle Mariners are in win-now mode at the major league level rather than looking more toward the future.

The graduation of many top prospects, particularly on the pitching side, has left Seattle's farm system a little thinner than it has been previously. While the Mariners in no way have a bad farm system and haven't been trading away too many prospects, most of the exciting young players are in the majors.

Still, Seattle entered the year with several prospects who were worth keeping an eye on. D.J. Peterson and Patrick Kivlehan appeared not all that far off from appearing in the majors, while top prospect Alex Jackson figured to move up to more advanced levels.

For many of Seattle's top 10 prospects as determined by MLB.com, the season has gotten off to a disappointing start. Others like Ketel Marte and Edwin Diaz could soon be moving up prospect rankings.

Alex Jackson, Outfield

2015 stats (Single-A): .157/.240/.213

The Mariners felt fortunate to have Alex Jackson fall to them with the sixth overall pick in the 2014 draft. As the top high school bat in the draft, Jackson was a few years away from being in the majors, but he instantly became Seattle's best prospect in terms of potential.

He largely backed up the hype in his brief debut last year, despite missing a month after being hit in the face with a line drive. Jackson hit .280/.344/.476 with 10 extra-base hits in 94 plate appearances en route to being named the Arizona Rookie League player of the year.

Things have not gone as well for Jackson this season following a move to Single-A Clinton. Through 121 plate appearances, Jackson has posted a .453 OPS with just six extra-base hits—all doubles.

The entire profile so far this year is a concern, but the lack of power really stands out, as scouting reports raved about the amount of pop in Jackson's bat. Jackson turned 19 years old in December and was playing high school baseball this time last year, so there's no reason to be too worried by the poor start.

Stock: Down

D.J. Peterson, 3B/1B

2015 stats (Double-A): .236/.303/.309

Unlike Jackson, D.J. Peterson entered the season with a chance to move to the brink of the majors. However, he has also struggled mightily in the early going.

After posting a solid 126 wRC+ in his first 58 games of Double-A last season, Peterson has put up a mark of 69 through 127 plate appearances at the same level this season. Peterson's strikeouts are up so far, while his walks and power numbers are down.

Such a slow start from Peterson is less concerning than Jackson's, as he has already proven he can hit at the Double-A level. There's no use in sending Peterson back to High-A, so the Mariners will just have to wait out the slump.

After hitting his first home run of the year on May 1, Peterson told Josh Jackson of MiLB.com that he is typically a slow starter.

"It seems like every year I start off in a bit of a struggle because I come out trying to do too much," Peterson said. "I'm just trying to get the train back on track and help this Double-A team win. ... I've been trying to simplify the game and not try to do too much. I'm just trying to have fun and get back to basics."

Stock: Down

Ketel Marte, SS/2B

2015 stats (Triple-A): .352/.395/.421

Ketel Marte has slid under the radar as a third promising young shortstop in Seattle's system behind Brad Miller and Chris Taylor. While Marte will have to battle for playing time for the foreseeable future, what he has accomplished so far is very impressive.

At just 20 years old, Marte put up a solid .302/.329/.404 slash line at Double-A and earned a promotion to Tacoma by the end of the season. Still at a young age for his level, Marte is having his best season as a pro with a 122 wRC+ through 162 plate appearances. He is hitting well from both the left and right side.

Marte has been excellent at making contact in his minor league career—his strikeout rate for this year stands at a minuscule 8.6 percent—and has the speed to steal over 30 bases in a season. His defense at shortstop would definitely be considered a weakness, but Marte is emerging as a clear future piece of the Mariners rather than an emergency option or trade chip.

There's some good news for Marte at the major league level as well. With Miller potentially transitioning to the outfield, Marte may only have to beat out Taylor for playing time in the years to come.

Stock: Up

Patrick Kivlehan, 3B/1B

2015 stats (Triple-A): .216/.281/.392

After getting off to a slow start in his professional career, Patrick Kivlehan put up arguably the best season of any Mariners prospect in 2014 with a 140 wRC+ in Double-A. That led to the thought of Kivlehan possibly getting some playing time in Seattle later in the summer, perhaps as a September call-up or a platoon partner for Logan Morrison should he struggle.

Unfortunately, Kivlehan has not hit well enough to justify such a promotion, posting a 72 wRC+ through his first 143 plate appearances at Double-A. There are some encouraging signs: Kivlehan has six home runs to rank second on the team and is maintaining good plate-discipline numbers.

Once again, there isn't much use in sending Kivlehan down to a level he has already proven himself at, so the Mariners will just have to wait it out. The leap between Double-A and Triple-A is a big adjustment, and Kivlehan is still displaying some skills to make him an intriguing prospect.

Stock: Down

Gabriel Guerrero, Outfield

2015 stats (Double-A): .207/.242/.328

Gabriel Guerrero has many traits reminiscent of his uncle Vladimir—he's a free swinger, possesses an absolute cannon for an arm and has plenty of pop in his bat. The 21-year-old proved he could get by on more than just name recognition in 2014 with a .307/.347/.467 line and 18 home runs in High-A.

The transition to the next level (and much worse hitting environment) has not been smooth. While Guerrero has struggled to get on base, he does have eight doubles and two home runs in 31 games so far in Jackson.

Guerrero is still noticeably raw and is pretty young for his level. The start is disappointing, but Guerrero has an exciting skill set that could develop nicely over the next couple of seasons. 

Stock: Down

Austin Wilson, Outfield

2015 stats (High-A): .200/.319/.250

Much like Guerrero, Austin Wilson has tremendous raw physical skills that are still developing. At 6'5", 245 pounds, the Mariners hope Wilson can eventually become a prolific power-hitting corner outfielder.

Wilson showed major promise in that regard in 2014, slugging .517 at Class-A Clinton. He has been unable to replicate the success at High-A, posting just a 58 wRC+ so far.

Like some others on this list, Wilson's lack of power has been the problem so far. Wilson is at least getting on base at a decent clip, but he needs to start showing more soon at 23 years old. 

Stock: Down

Edwin Diaz, SP

2015 stats (High-A): 1.70 ERA, 3.48 FIP, 29.8 K%, 6.4 BB%

With Taijaun Walker and James Paxton firmly entrenched in the majors—plus the unknown status of Danny Hultzen—Edwin Diaz takes over as the top pitching prospect in the organization. So far, he's justified his ranking.

Diaz blew threw seven starts at High-A, posting even better numbers than he did during a full season at Clinton in 2014. With a fastball in the mid-90s that he can command extremely well and a plus curveball, Diaz has already shown some advanced skills for having just turned 21 years old.

Those numbers earned Diaz an early promotion to Double-A, where he struggled mightily in his first start on Saturday. But the fact that he is moving along so quickly is a promising sign.

Stock: Up

Luiz Gohara, SP

Luiz Gohara pitched 37.1 innings at Low-A Everett last season and will apparently be staying there to begin 2015, as he has yet to debut this year. His stuff was good enough to generate nearly a strikeout per inning there last year, but Gohara has some work to do with his command after posting a walk rate of 12.8 percent.

Even at just 18 years old, Gohara stands at 6'3", 220 pounds with easy velocity in the mid-90s. If he can develop some other pitches and improve his command, there's a lot of potential here. 

Stock: Neutral

Tyler Marlette, C

2015 stats (High-A): .226/.299/.377

Tyler Marlette rose up prospect lists thanks to an impressive 123 wRC+ performance at High-A last season. The 22-year old has some pop in his bat and a good arm, and he is rapidly improving his receiving skills behind the plate.

After being promoted to Double-A for the final nine games of 2014 and hitting well in a small sample size, Marlette was sent back to High-A to begin the year. Marlette is having a much harder time with the new Bakersfield affiliate than he did at High Desert, posting a wRC+ of just 83 so far.

The good news is that Marlette has hit four home runs in the early going, and the most important thing at this stage is that he keeps improving his defense. Marlette has a future in the majors, but this season will be critical in his development. 

Stock: Down

Carson Smith, SP

2015 stats (MLB): 1.08 ERA, 2.31 FIP, 33.3 K%, 6.4 BB%

Carson Smith has lost his status as a prospect in 2015: He's reached the major leagues, and he is there to stay barring an injury. Not only has Smith carved out a spot in Seattle's bullpen, he looks like the most dominant reliever on the roster.

With unconventional arm action, an excellent slider and a fastball with speed and sink, Smith is a nightmare for right-handed hitters. In 26 major league innings in his young career, Smith has recorded 32 strikeouts while allowing just 16 baserunners.

The only question is when Smith will move to the closer role. 

Stock: Up

All stats courtesy of FanGraphs unless otherwise noted.