The line is usually stretched the length of the waterway, but again that is not the rule. The other end of the main line is usually tied to something that floats, like a plastic jug. In an improvised situation it could be secured on a bank or tied to a log snag out in the water. It is put in place in the evening and checked the next morning. When checking start at the end of the main line that is floating or tied off and pull the main line to the surface.
Trotlines are a good piece of equipment if the survivor has enough hooks, bait and stout cordage.
Treble hooks work the best for this type of application. Hand Fishing Hand fishing is a very good method for collecting fish. It is easy and once the first fish is caught by hand it will become a favorite technique of the survivor. Just getting an individual to try it seems to be the biggest hurdle. Basically a hand is slowly reached into likely spots that lounging fish stay.