After struggling to do much of anything right in Tacoma, Bucky was outrighted off the 40-man roster to make room for Mike Morse (post-suspension).
So, as you probably deduced, the roster is full, with Chris Snelling, Jamal Strong, Pokey Reese, Bobby Madritsch, Travis Blackley, and Jorge Campilo all on the 60-day DL. Reese won't be coming back, but space will need to be cleared for the other five upon their eventual returns.
The good news is, the team shouldn't have any trouble paring down this offseason, as it's unlikely that any of Cha Baek, Shigetoshi Hasegawa, Matt Thornton, Jeff Nelson, Jeff Harris, Dave Hansen, Justin Leone, Masao Kida, Ramon Santiago, and Jaime Bubela stick on the 40-man into next season. Throw in some bubble players (Ryan Franklin, Gil Meche, Francisco Cruceta, etc.) and the Mariners shouldn't have too much trouble making offseason additions while avoiding Rule 5 vulnerability.