I haven't caught one again, but then again I normally have at least a few LMB following me around the pond and they'd get eaten with or without a tail. But, if you want the LMB to eat small BG, with you tossing them back in for the LMB to eat is no different than just letting them catch them on their own. If you were to remove them, then the LMB would need to look for another BG to eat, so you're removing 2 instead of just 1.
