I always check the stomach contents of the fish I catch and fifty prcent of the time they are empty. The ones that do have undigested food in them usually have been feeding on candlefish. I dont think that your concerns about blackmouth are valid. It's been my experiance that the smaller smolts cruise in the top fify feet and the larger blackmouth are on the bottom most of the time (feeding on candle fish which are much more numerous and slower) thus mother nature has separated them on in her own way