I would sooner think that it was snached off the fish as it came up to look at the spoon. They don't look like the fastest swimmers in the pond, more like a bushwacker type
The chrome piece dosen't unscrew off the mast. The nylon piece should come out of it with out much trouble. The coax cable comes out of the mast above the mount so you shouldn't have to cut or splice it once you get your new mount installed
Some of the streams get locked with gravel at the end and the fish can't get in . They would look for the next best flow when the spawning erge got too strong