There are two main jobs on a fishing boat.
One is to “cut bait,” which means to prepare or cut “junk” fish for a hook, or for “chum,” which is dumped in the water to attract other fish.
The second job is to do the actual fishing.
So the admonition “Either fish or cut bait” doesn’t mean either fish or cut your line.
It means make up your mind and decide which job you’re going to do, and just do it.