The board of directors of a credit union shall fill any vacancies occurring in the board until successors elected at the next annual election have qualified. If more than fifty percent of the board positions become vacant at any one time, a special meeting of the members shall be called to fill all vacancies. The supervisory committee shall fill all vacancies in its own membership as they occur. If all of the supervisory committee positions become vacant at any one time, the board of directors shall fill all vacancies, and those appointed members may serve until the next election. The board shall fill vacancies occurring on all other committees.