PORT ST. LUCIE, Fla. -- To fill a bullpen void, the Mets looked outside their clubhouse this weekend -- but not too far outside it. The Mets and Yankees completed the 16th trade in their collective histories, sending right-handed reliever Miguel Castro to the Bronx and lefty Joely Rodríguez to Queens.

For the Mets, the deal adds left-handed depth to a bullpen that was lacking it. Before the trade, the Mets had no lefty relievers on their Opening Day roster and only two in camp: Chasen Shreve and Alex Claudio, who are both non-roster invitees on Minor League contracts.

Rodríguez, 30, posted a 4.66 ERA between the Rangers and Yankees last season and has allowed five runs in two appearances this spring. But the Dominican native thrived against left-handed hitters in 2021, holding them to a .203/.288/.271 slash line. Compare that to right-handed batters, who tagged Rodríguez for a .339/.380/.446 line last season.

“We had been talking a little bit about some of the excess left-handers that the Yankees have had,” Mets general manager Billy Eppler said. “Clearly, left-handed relief was something that we were looking for. We were able to find a trade partner, and oddly enough, it was across town.”

Castro, meanwhile, is coming off a year in which he set career bests with a 3.45 ERA and 77 strikeouts. He was actually more effective against lefties than righties, holding them to a .198/.313/.270 slash line -- though historically in his career, that hasn’t been the case. Eppler noted that the Mets looked deeper into Castro’s history against lefties, including his walk rate, strikeout rate and quality of contact, when evaluating the trade.

The Yankees, meanwhile, needed right-handed relief help with Zack Britton recovering from Tommy John surgery. Both Castro and Rodríguez can become free agents after the season.

“He can be very deceptive with that delivery, that arm slot, the components of his fastball,” Eppler said of Rodríguez. “He looks like he can be somebody that can help us a lot, so we grabbed him.”

• Breaking down the history of Yankees-Mets trades

In Flushing, Rodríguez is a sure bet to be on the Mets’ season-opening 28-man roster. Shreve can still make the team as well, which is a decision the Mets will have to finalize soon. If the Mets don’t add Shreve to their 40-man roster by midnight on April 4, he can opt out of his deal and look to sign elsewhere. If that happens, the Mets would have an additional 24 hours to change their minds and add Shreve.

Rodríguez’s presence does decrease the chance of Claudio making the roster, despite a strong spring that has seen him fire five shutout innings.

In some ways, it’s notable simply that the Mets and Yankees completed a trade. They had done so only 15 previous times, most recently in 2018. The vast majority of those deals have been minor, with one notable exception: David Justice for Robin Ventura in 2001.

Perhaps with Eppler running things in Queens, however, that could change. Before coming to the Mets, Eppler spent 11 seasons working under Yankees GM Brian Cashman, with whom he maintains a strong relationship.

“It was unique,” Eppler said of dealing with his former boss. “But I think on the surface, we were serving each other’s needs is what it seemed like, to me. They wanted to get a little more right-handed. We wanted to get left-handed. The circumstances just aligned.”