FishingRod,

Provided prey is large enough to be retained by gill rakers and small enough to fit in a predators mouth and be passed into the gullet ....it constitutes potential food. If an LMB takes food in its mouth, it makes sense to swallow it if it can be swallowed in order to get the energy return of an energy investment. I would think that LMB which are guarding nests typically do not get a full daily ration and that such LMB may be declining. There is incentive to feed from that stand point if it does not risk the nest. IOWs it makes sense that it isn't purely for defense but a blend of defense and some needed energy for the task of nest tending.

I will mention that on most days that I fly fish I will hook up with a >16" LMB or >22" CC. The CC are much more rare however and it seems I only hook up when the light is very low near dusk. I have caught several >16" LMB this year on a size 14 copper john. That's ultra tiny. On Saturday, I shouldn't have went out because I was coming down with Covid and it was dang hot ... but I netted some GAM and fished for small LMB to stock a pond and for >16" LMB to remove. I am trying to shift the population structure in favor of BG growth. Anyways the gams ranged in size from 3/4 in to 1 1/2 inches. I caught 8 LMB ranging from 3" to 8" ... but guess what? I also caught a 12" LMB and an LMB > 16". I deliberately fished for both casting to them and both spotted the GAM and moved in to investigate. Stopping just short. Then each opened its mouth moving forward a little with a small flick of its tail engulfing their respective GAM. The GAM that caught the 16" LMB was less than 1 inch long and was a negligible proportion of its daily maintenance need. I don't know why fish that large take size 14 copper johns and little GAM ... but ... if we return to optimum forage theory we might come to the conclusion that the LMB taking these baits anticipated a net gain in energy.

My efforts to remove 16" LMB from the little pond didn't go as well. There is a huge bloom of BG in that pond from 1/2 in to 1.5in in length and it is very difficult catch BG that small for fishing but I did manage two but was broke off by two that were the size I wanted to catch. The roughly 1.5" BG I was using were near the lower limit of what is considered consumable (10% proportionate length). I was unable to catch BG at the optimum length. That segment of the population is not very numerous right now.