jpsdad,
Yes I understand that large LMB target the optimal size of BG forage for them.
However, I think I am missing some step in the progression.
If the LMB are predominantly eating the 3-6" BG, then I would expect a very heavy population of 2-3" BG. You frequently provide excellent data on the feed consumption required to increase the size of LMB. Apply those principles you vividly describe to the BG.
What I don't understand is how the 2-3" BG increase in size? If there are thousands of them in the pond, I would expect that they quickly consume all of the forage that is "right sized" for them. How do the small BG find enough calories to increase their size to become large BG? Is the productivity of a fertile pond sufficient to create a large enough natural food chain to amply supply calories for each size cohort of forage fish?
Sure. The first thing I would point you to is Anderson on Population Structure (PSD). He more or less wrote the book on this and others have expanded. They separate fish classes based on length ranges (Stock, Quality, Preferred, Memorable, and Trophy). For BG the stock designation begins with 3" and ends with 6". BG that are below 3" in length are not counted. You may ask why?. Well for one thing they comprise a very minor portion of the biomass even when they greatly outnumber all the rest of the population combined. Second, they fluctuate due to predation. At swim up there may be millions. But when a single 4" BG can eat 2200 of them an hour, they get whittled down fast. Only a minor fraction of them survive to grow beyond 1". If there is a sufficient biomass of BG in the 3-6" range, it is possible that none of the millions grow beyond 1" until the 3-6" fish are thinned down by predators. Generally speaking the biomass of 1-3" BG is always small when there is a sizable population of BG in the pond. Take a look at the image below where I depict different balance strategies as proposed by Anderson in a graph.
![[Linked Image from i.imgur.com]](https://i.imgur.com/M97Z2pG.png)
What I would like for you to notice is how populated the 3" to 6" are in the BIG BASS scenario. They are 25 times more populous in the Big Bass scenario than in the Big BG. Why? Because there are not enough small LMB to prevent their recruitment into the 3-6" stock class. Why does the stock class of BIG BG scenario have so few? Because there are enough LMB to prevent most all that grow larger than 1" from growing to 3". I did try to explain this before, so this is very important. The juvenile class of BG plays the pivotal role for recruitment of BG > 30mm (1.2"). When they are numerous much fewer are recruited to the 1-3" sizes. So the BIG BASS scenario both doesn't need to nor does it actually recruit as many 1" BG as the BIG BG scenario. This seems counterintuitive but it is natures balance. When LMB are less numerous, few numbers reach 1" but greater numbers reach 3". The opposite is true when LMB are more numerous. Much larger numbers of BG reach 1" but far fewer numbers reach 3". This is essential for balance under various predator densities and Nature has this baked in. Isn't this just beautiful how Nature works?
Now you asked:
How do the small BG find enough calories to increase their size to become large BG? Is the productivity of a fertile pond sufficient to create a large enough natural food chain to amply supply calories for each size cohort of forage fish?
As I said before, they have minor biomass and so can easily grow on things we call first consumers. They get more out these small creatures than larger BG can. There is almost always plenty of food available to BG of small sizes. That is why they grow at such remarkable rates of growth.
When I first started studying Anderson, one thing stood out. He stated that when a pond was balanced and running on all cylinders, the carrying capacity was about 50% full. I have since really learned to appreciate this. Consider this, at 16% of a ponds biomass, LMB must consume 80% of the biomass yearly in order to tread water and maintain their weight (at 5 lbs BG per 1 lb LMB). Now stop just for moment and contemplate the magnitude of this consumption need. If the biomass proportion of LMB is 16%, then the biomass proportion of the BG is 84%. IOWs, for maintenance the LMB need 95% of the standing weight of BG every year. Let that sink in.
Because we know that most of the BG population is to big for the LMB to eat, there is only one way this can happen. Large numbers of small BG must grow and die as LMB prey that are not part of this adult population. Now in this context what Anderson said about 50% of the carry capacity makes sense. The 50% of unused carry capacity is growing a weight of consumable BG that is very nearly equal to or possibly exceeds the standing of adult BG that are too big to eat. That's where the food comes from to grow the consumable sizes. It comes from reserved unused carrying capacity. So when we say carry capacity for BG, we really do mean the carry capacity of BG under predation. For a pond that carries 300 lbs of BG and 50 lbs of LMB, this same pond might max at 600 lbs BG with no LMB present. Its counter intuitive, and few here agree with me, but I have argued for a long time that it is important to ensure that the adult BG population does not become excessive. I will always stand by that even though I am a minority on that position.
