There is a scoreboard that can be used called minecraft.used:minecraft.fishing_rod and it is meant to detect whenever a fishing Rod is used. It is supposed to increment by 1 every time the fishing rod is used. However while testing I have found that the increment only happens when the rod is initially cast out, and when reeling back in although the rod is technically being used it does not increment the counter. I do not know whether this is intentional or a bug, but i personally believe it to be a bug.