The crews I work with are kept very small because we need to be highly mobile, and because fish are wild animals, which don't respond well to lots of people in the vicinity. And because people and equipment are expensive to move. Crew members are hired by the production company I work with, and all are experienced (and often multi-tasking) directors, camera operators, sound recordists, assistant producers or production co-ordinators, who have usually worked their way through the ranks. Many started as 'runners' (general odd-job staff) for TV production companies, a good way to get a start in this industry, although competition for these positions is fierce.