The Mariners arrive in the Bronx this week as the AL’s most pleasant surprise, in part because of the depth of the Yankees.

One reality of building a deep roster and farm system is you can’t keep them all — only 25 on the active roster and only 40 on the major league roster.

The Cubs, for example, constructed a powerful everyday lineup, allowing them to trade from young positional depth. Gleyber Torres has emerged as an AL Rookie of the Year front-runner with the Yankees. Jorge Soler led the Royals in OPS-plus when he fractured a bone in his foot over the weekend. Jeimer Candelario was second on the Tigers in OPS-plus. And Eloy Jimenez was the MLB’s fourth-ranked prospect to begin the season and had a .925 OPS at Double-A for the White Sox.

Teams with deep systems are going to populate a lot of rosters, and no organization is currently doing that like the Yankees. And no team has benefited more than the Mariners. Ben Gamel, James Pazos and Nick Rumbelow were all traded to Seattle for the same reason: The Yanks were facing a 40-man roster crunch and did not want to risk losing them in the December Rule 5 draft for nothing.

“No question, you can’t keep them all,” Brian Cashman said. “You have to constantly manage your roster and you don’t just want to lose someone in the Rule 5 draft. Another team will take the talent out of you and you might never see it again. You either make the best trades you can or you run a real risk of losing them for nothing.”

Wade LeBlanc used his opt-out clause late last spring when the Yanks informed the non-roster invitee he would not make the 25-man roster. Seattle GM Jerry Dipoto had already had him when he was the Angels GM and with the Mariners. Facing staff injuries, Dipoto signed him again.

Rumbelow only came up recently. But Gamel had a 119 OPS-plus as Seattle’s regular left fielder. Pazos has emerged as a top lefty reliever (1.48 ERA). LeBlanc is 3-0 with a 2.63 ERA (2.06 as a starter). He blanked Boston over 7 2/3 innings on Saturday night.

Dipoto’s ability to forge roster depth has enabled Seattle to thrive despite the loss of another player developed by the Yankees, Robinson Cano, who is in the midst of an 80-game suspension for testing positive for an illegal performance-enhancing drug.

“Give Jerry Dipoto a lot of credit,” Cashman said. “We had roster issues and we got calls on [the borderline guys]. Credit to Jerry Dipoto for being the most aggressive. He won the day with the best offers.”

LeBlanc — unlike Gamel, Pazos and Rumbelow — did not sign his first pro contract with the Yankees. Still, through Sunday, the Yankees had the most original signings who played in the majors this year at 52 (the Rangers were second with 49, followed by the Cardinals at 48 and Mets at 47). Thirty-five had played for teams other than the Yankees. Caleb Smith, for example, was going to have difficulty staying on the Yankees’ 40-man roster, so they traded him to the Marlins, where he is blossoming into a valuable starter.

Nevertheless, the Yankees had four players taken in each of the last two Rule 5 drafts. The eight total was six more than any other team had drafted. The Yankees got seven back after they failed to make the rosters of the team that selected them. They lost only catcher Luis Torrens to the Padres, but that underscored that with more teams in tanking mode, more are willing to stash a Rule 5 pick for the season.

The Yankees also had 13 players they had traded among the top-30 prospects of other organizations (via MLB Pipeline). Some would not have made the Yankees’ top 30. One team’s organizational depth is another’s gem. Taylor Widener was ranked the Yankees’ 14th-best prospect when he was part of the offseason trade for Brandon Drury. He is fourth with Arizona.

The Yankees have been willing to package prospects such as Jorge Mateo, Dustin Fowler and James Kaprielian — all in Oakland’s top 10 — for Sonny Gray because they believe they have better at their positions and because keeping everyone with 40-man restrictions is implausible.

Drury (.999) and Clint Frazier (.947) rank 1-2 in the International League in OPS (minimum 160 plate appearances). They are essentially major leaguers who are blocked with the Yankees and thus viable trade candidates over the next few weeks. This is quite different from most of Cashman’s two-plus decades as Yankees GM, when they were top-heavy but lacking in organizational depth.

“It is a double-edged sword and more challenging for us,” Cashman said. “You have to make earlier calls [on whether to keep or move players] before you would like to. You just have to make the best call.”