The Bruins acquired Jaromir Jagr from Dallas Tuesday. They might not be done dealing. The Bruins still need help on defense, specifically a left-shot defenseman. Islanders captain Mark Streit, an unrestricted free agent at the end of the season, could be atop their wish list. For the last two postseasons, the coaching staff has paired Zdeno Chara and Dennis Seidenberg as an ace shutdown duo. This year, while Chara and Seidenberg have played together in stretches — the two strongmen have been paired late in games when the Bruins have led — they have not been a regular duo. Most recently, Chara has been taking the majority of his shifts alongside Dougie Hamilton. Seidenberg has been paired with Matt Bartkowski. If Chara and Seidenberg are reunited, Bartkowski, Andrew Ference, and Aaron Johnson are left-shot defensemen in the mix for playoff minutes. Ference is the only sure thing. Bartkowski and Johnson have been healthy scratches. Ference could skate with Johnny Boychuk on the No. 2 pairing. Hamilton would be the right-side defenseman on the third duo. The Bruins would prefer a veteran defenseman over Bartkowski and Johnson in the playoffs. Streit has five goals and 13 assists in 36 games while averaging 24:06 of ice time per appearance. The Bruins explored signing Streit as a free agent in 2008. Instead, they signed fellow ex-Canadien Michael Ryder on July 1, 2008. The Islanders have not been successful at signing Streit to an extension.