As much of a staple this spell is for fishing, it really needs an improvement. I think the beams should be persistent over a period of time. It's pretty much impossible to memorize the locations of all the target fish and track them while they're out of your field of vision, so the spell is only good for 2-3 casts. An alternative fix would be to allow movement during the spell so you can scare away the "junk" fish.