Team captains are voted on by the players. Here are the captains for the 2015 season:
Offense
Joe Staley
Anquan Boldin
Vernon Davis
Colin Kaepernick
Defense
Antoine Bethea
NaVorro Bowman
Eric Reid
Ian Williams
Special Teams
Team captains for season (player vote): Off-Staley, Boldin, V.Davis, Kaepernick. Def-Bethea, Bowman, Reid, IWilliams. ST-Dawson.
— Matt Maiocco (@MaioccoCSN) September 8, 2015