The Mariners added four prospects to their 40-man roster Tuesday afternoon, a few hours in advance of the Major League Baseball deadline for teams protect players from the upcoming Rule 5 draft in December.

The Mariners selected the minor league contracts of:

  • Prelander Berroa, RHP
  • Isaiah Campbell, RHP
  • Jonathan Clase, OF
  • Cade Marlowe, OF

A week ago at the MLB general managers meetings, Mariners president of baseball operations Jerry Dipoto confirmed that Berroa, a hard-throwing right-hander acquired in a May 11 trade with the Giants for infielder Donovan Walton, would be protected by being added to the 40-man roster.

Berroa, 22, posted a 3-3 record with a 3.19 ERA in 22 starts combined between High-A Everett and Double-A Arkansas and is rated as the No. 13 prospect in the organization by Baseball America.  

In 87 1/3 combined innings, Berrora struck out 134 batters with 57 walks. He held opponents to a .163 batting average.

He was recently named the Northwest League Pitcher of the Year after posting a 2-2 record with a 2.06 ERA (15 ER, 65.2 IP) in 17 starts combined between Eugene (Giants affiliate) and Everett. He combined to limit opponents to a .153 batting average while striking out 97 hitters and walking 38.


After being promoted to Arkansas, he combined with four pitchers to toss a no-hitter vs. Northwest Arkansas on Aug. 12. He tossed five innings, walking two batters and striking out 11.

“It’s an electric arm, which was the attraction,” Dipoto said. “We are trying to work on his command. When he’s going good and he’s locating, he’s as good as anybody in our system.”

Berroa has a fastball that can run up to 100 mph and a nasty breaking ball, but lacks a quality third pitch. He could be converted to the bullpen in the future.

“Our thought is, if he is a starter, it’s impact stuff,” Dipoto said. “And if he is a reliever, it’s an impact role because we think his strikes are good enough to make an impact in the back of the bullpen. And if the third pitch comes along in a meaningful way, then really the sky’s the limit for what he could be because he’s got a great arm.”

Marlowe, 25, traveled with the Mariners during the postseason as a member of the taxi squad. With his speed and ability to play all three outfield positions, the Mariners considered activating him for his MLB debut in the American League Wild Card Series in Toronto.

“I would have loved for that to have been my first couple of weeks of exposure to the big leagues,” Dipoto said. “Cade is a multi-talented player with a great makeup, which is the first thing that comes to mind. He can play all three outfield spots, he can run. He’s a good base stealer. He’s got power and he controls the strike zone. We think he has the upside potential to be an everyday outfielder.”


Marlowe played 120 games with Arkansas and was promoted for the final 13 games of Class AAA Tacoma’s season. In those 133 games, he posted a .287/.377/.487 slash line with 21 doubles, five triples, 23 homers, 83 runs scored, 103 RBI, 62 walks, 156 strikeouts and 42 stolen bases.

Marlowe, who is rated as the No. 20 prospect in the Mariners organization, was a 20th-round pick in the 2019 MLB draft out of West Georgia University and will likely make his MLB debut at some point in 2023.  

“He went from a curiosity in his early days as a later round pick, who was really performing well as an older prospect at the lower levels to making himself a legitimate prospect,” Dipoto said. “He’s put himself at the doorstep of playing in the big leagues. He has the ideal skill set to enter the big leagues as an extra outfielder and work his way into playing time because he can play all the spots and he can run.”

After being delayed in his start to his professional career coming out of the University of Arkansas as the 76th overall pick in the 2019 draft due to usage and later battling arm issues in 2021, Campbell, 25, converted to a relief role in 2023 and flourished.

He made four starts for Everett, posting a 1-0 record with a 1.50 ERA. But elbow inflammation forced him to the seven-day injured list. He returned on June 4 as a reliever and dominated, pitching 15 scoreless innings in 15 appearances. That stretched included going 10 for 10 in save situations where he struck out 20 hitters with one walk.

He was recently named to the Northwest League All-Star team.

The Mariners moved Campbell up to Double-A Arkansas on Aug. 1. He appeared in 14 games, posting an 0-4 record with a save and a 3.46 ERA.


Clase, 20, is rated as the No. 15 prospect in the Mariners organization. He is one of the fastest players in the organization on the bases or in the field. With the new rules about limited pickoff throws and bigger bases being implemented, his value should only increase.

In 107 games with Low-A Modesto, he posted a .267/.373/.463 slash line with 22 doubles, 11 triples, 14 homers, 91 runs scored, 49 RBI, 65 walks, 133 strikeouts and 55 stolen bases. The 55 stolen bases and 11 triples were the most in the Cal League.

The Mariners signed Clase as an international free agent on July 2, 2018, out of Santo Domingo in the Dominican Republic.