The manual details biographies on 10 "head" crewmembers, which crew the 5 6 stations (except computer) aboard the ship, 2 for each station . Upon starting a new game, the game will randomly pick which person from among the two will crew a station. This is done despite the biographies in the manual giving a good idea of who would have seniority and be the head of their department. Maybe they just don't like sitting on the bridge.
You can manually change who's manning a station by sending one of the crewmembers a Add