"It's very challenging in this day and age to have catching depth," said Mariners general manager Jack Zduriencik. "To add a catcher that has a reasonable amount of Major League experience is important to the entire organization."
"It gives us a lot more depth in our organization as a whole," added manager Lloyd McClendon. "From that perspective, it's a pretty good darn baseball move. To think how physical and tough catching is and the number of catchers that have gone down this year, if something were to happen to Zunino I'm not sure that we had the depth in our Minor League system that would be ready to perform at this level. So we think it's something that's going to be real good for our organization."
Castillo has hit .163 with two home runs, two doubles and five RBIs in 24 games for the Cubs this season. He was the Cubs' starting catcher in 2013-14, batting .274 in '13. But Castillo's offense dropped last year when he hit .237, and he was working as the team's third catcher this season behind Miguel Montero and David Ross.
McClendon made it clear that Castillo was acquired to serve as the Mariners' backup.
"His playing time will be predicated by Zunino's performance on the field," McClendon said. "We're not fooling anybody here. Mike Zunino is our everyday catcher."
Medina, 26, was a key member of the Mariners' bullpen the past two years, but he was sent to Triple-A Tacoma two weeks ago. Seattle has some strength in its right-handed power arms, but Zduriencik said it was still a tough decision.
"I don't think anybody is comfortable with having enough pitching," Zduriencik said. "But catching at the Major League level is a very challenging position. It's difficult to get through the season with one or two catchers. We've been fortunate to have a healthy Mike Zunino, but a couple years ago, he was out six weeks with a broken hamate. It's a position on the field where if you can add depth, it's in your best interest to do it."
The Mariners currently have John Hicks, who has no Major League experience, and veteran John Baker sharing backstop duties at Tacoma. Hicks is hitting .226 with a .674 OPS in 24 games, while Baker has batted .161 with a .378 OPS in 17 appearances.
Seattle hasn't got much offense out of the position at the Major League level either. Zunino is a well-regarded 24-year-old and excellent defender, but he's batting just .179 with a .600 OPS in 35 games. Sucre has hit .067 (1-for-15) with a .133 OPS in six games.
Castillo has a career .252 average with 29 home runs and 110 RBIs. From 2013-14, he hit .255 with 42 doubles, 21 home runs, 78 RBIs and a .716 OPS in 223 games. The Dominican product has thrown out 58 out of 220 attempted basestealers in his career (26.4 percent).
"He has the ability to hit, and he's got power," Zduriencik said. "He has a very good throwing arm and is a good [pitch] blocker. He has a nice skill set. There are those that debate whether he could have been a starting catcher at this level. I think we're getting someone with ability, and we'll see how he fits in with our club."
Medina posted a 2.82 ERA in 141 appearances out of the Mariners' bullpen the past three seasons. This year, he was 1-0 with a 3.00 ERA in 12 innings over 12 outings with Seattle, and he had a 1.59 ERA in 5 2/3 innings over four appearances with Tacoma. Medina will be assigned to Triple-A Iowa by the Cubs.