The Cubs created a big hole in the bullpen when they traded left-hander Sean Marshall to the Reds. The move left them with three southpaw relievers on the 40-man roster: Scott Maine, John Gaub and Jeff Beliveau.

Maine added velocity to his fastball and bite to his slider in 2010, earning a late-season call-up. His low-90s heater and improved slider helped him post a 2.08 ERA in 13 innings with the Cubs.

Maine received his second taste of the big leagues last May, but spent most of 2011 in Triple-A Iowa, where he posted a 12.6 K/9 and 3.68 ERA in 51.1 innings. 

Gaub came to the Cubs in the Mark DeRosa trade following the 2008 season. He ranked as the organizations’s No. 14 prospect according to Baseball America prior to 2010, but has failed to crack the publication’s top 30 list in each of the last two seasons. His fastball sits in the low-90s, but his mid-80s slider is his go-to pitch. In three seasons with Triple-A Iowa, Gaub has posted a 3.73 ERA and a whopping 11.9 strikeout rate. His bug-a-boo? An unsightly 6.3 walk rate. 

Beliveau is the most promising in-house option. After posting a career 4.8 walk rate in the lower levels of the minors, Beliveau finally reached Double-A as a 24-year-old last year, showing improved control (2.1 BB/9). His 10.9 K/9, 1.89 ERA and 0.87 WHIP led to him being named the organization’s minor league pitcher of the year.

According to Baseball America, Beliveau didn’t allow a single free pass to a left-hander in 100 plate appearances last season. He throws an 88-91 mph fastball which generates swings and misses “because it looks like it’s coming out of his sleeve.” The former 18th-round pick also features a deceptive change and mixes in a curveball with recently-added depth. 

If the Cubs don’t feel comfortable starting the season with Maine, Gaub or Beliveau as their primary left-handed reliever, they’ll have to seek a trade or sign a free-agent. The top available lefty relievers include: Mike Gonzalez, Hong-Chih Kuo, Damaso Marte, Arthur Rhodes and Brian Tallet. 

There’s also a possibility that Paul Maholm or Travis Wood (both lefties) could wind up in the bullpen. Assuming the Cubs don’t trade Matt Garza before opening day, Randy Wells, Chris Volstad, Maholm and Wood will battle for the last three spots in the rotation (Ryan Dempster is the No. 2 starter). 

As long as Beliveau doesn’t implode in spring training, my guess is he’ll get a shot to serve as the Cubs’ primary left-handed reliever.