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jpsdad Offline OP
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So everyone knows that I like to use known principles and then apply the theoretical math in spreadsheet form in order to formulate strategy to achieve preconceived goals. To be sure, reality doesn't always match the plan but it is useful to understand the limitations and so a preconceived plan working at optimum efficiency provides the rosiest possible outcome given a set of reasonably assumed constraints. In as much as this is true, we can arrive at understandings of what will not happen under a given strategy which is even more useful than understanding what is going to happen. I say this is more useful because sometimes it is difficult to understand that management methods/actions cannot produce our preconceptions in the real world.

We all know that predator growth and ultimate weight are determined by the population of predators and the production of forage. It takes so much to maintain the metabolism of a predator (let's assume 5 lbs/annum) and so much to grow a predator (let's assume 10lbs per pound gained for forage consumed above the maintenance requirement). Let's use LMB as the predator and lets us assume, as with a put and take system, we have complete control of the recruitment of predators via stocking 0 year females in the fall. As a sustainable management system, let us assume that the stocking regimen of x number of fish/acre has been followed for a sufficient length of time that the population reflects x number of LMB in each year class with harvest in the y year. So the y year represents the limit of time the predator is allowed to live in our pond. So under the strategy we envision either a natural mortality at the end of expected life (completely catch and release) or at a predetermined time where trophies are harvested and killed by the angler. We can play with this number depending on goals and learn the limitations and requirements of each in the rosiest potential outcomes. If we find we cannot reach goals in the rosiest potential outcome, then we know under what population or forage production conditions a particular method of management will fail ... and why it will fail.

[Linked Image from forums.pondboss.com]

So let's begin with an 8 year cycle where LMB of 8 years are harvested at completion of the 8th year depicted above. The growth per year is determined by the carrying capacity and the population. In the SS it is assumed that the magnitude of growth is the same in each year but you may notice that the percentage gained early in life is greater than later in life. This can be expected because the prey are YOY or BG that have not yet reached their second year. The smaller a fish is, the better its access to prey because new crops must grow past the smaller predators first. In the example, only one predator is recruited (stocked female) annually. To support the scenario, approximately 8000 BG must be produced annually in the appropriate sizes. Here I assume 18% the length of the LMB as the mode of the distribution of sizes consumed. To grow by 100% an LMB must consume 9.2 BG/day across the 180 day growing season ... while to grow by 11% requires the consumption of 4.4 BG/day. It takes a fair number of BG per LMB and it is the number they eat that determines how much they grow. One of the things I noticed is that limiting the number of LMB, limits the number of BG that are required. We can see this particularly by looking at a scenario that allows very little growth where the LMB are consuming just a little more than a maintenance ration.

[Linked Image from forums.pondboss.com]

So in the scenario above there are just too many LMB (64/acre) to support large LMB in a pond that carries 49 lbs/acre of LMB. One of the more interesting things though is what I previously mentioned. The number of BG required to sustain the LMB is dramatically increased. It now takes 5 times as many forage BG to support a pond with many small bass as it does to support the same weight of trophies. Are you surprised by that? Most people think that a stunted LMB pond doesn't produce enough BG. But the reality is that many more BG are produced because the standing weight of BG adults are relatively low as compared to the trophy pond. The BG standing weight is held below the carrying capacity and the BG adults grow large, are in good condition, and produce prodigious quantities of YOY. Were this large number of BG not produced the large number of LMB simply would not be maintained. So we KNOW this must be the case, the production of BG YOY is very large its just that there are so many LMB that few make it past 3".

So the next scenario is a trophy pond that one never keeps a trophy. We will allow the LMB to reach the ripe old age of 11 years at which point they die of natural causes and are no longer supported by the pond or consume prey.

[Linked Image from forums.pondboss.com]

Notice that in this scenario more of the prey consumption goes into maintenance and less goes into growth. So by not harvesting at the end of year 8 we are requiring a much larger proportion of prey to be used in maintenance of the greater number of predators. Allowing the LMB to reach their age limit would not increase their size even though the annual stocking rate is the same as our original example. It would take a pond with a higher carrying capacity to grow LMB as large as the original scenario if they are allowed to die in year 11 (as opposed to year 8).

So I ask you, what happens if we harvest in year 5? Is it possible grow LMB to the same size as the 8 year trophy pond? The answer is yes provided the annualized average growth is attainable. So the example below may require Florida genetics but at a stocking rate of 1.5/acre (3 per 2 acres) the LMB could achieve >10 lbs in the 5th year with annual growth of 1.84 lbs/year. What is interesting is the annual harvest of >10 LMB is 50% greater than the 8 year scenario even with a decrease in required forage consumption. The population is also almost as great with a reduction in the population of only 1 LMB per 2 acres. The needed number of BG forage individuals is practically the same. So why is the 5 year system better than the 8? The primary reason is that it is more efficient. There are three maintenance years absent relative to the 8 year system and so a higher proportion of an equivalent amount of prey can be used for growth instead of maintenance. It is very difficult to convince one that trophies can be harvested. I guess where a pond is doomed due to over recruitment this may be the case. No new trophies are going to produced anyway. But if recruitment can be controlled as here modeled ... new trophies will be grown annually. It is worth noting that the 5 year example REQUIRES harvest of 5 year LMB. This is because the annually stocking rate is 50% greater and so if they are not harvest after completion of year 5 ... they can not achieve as great an ultimate weight as presented in the scenario.

[Linked Image from forums.pondboss.com]

Last edited by jpsdad; 06/22/21 06:51 PM.

Common sense is not so common - Voltaire

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers


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You ought to tell us about your pond sometime.


"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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I love stuff like this, well done. So, by not harvesting 8-year-old Bass, you're hurting the growth of the rest of your Bass? I think there are a lot of variables that can't be plugged into an Excel Spreadsheet, such as the weight of each BG consumed. Larger bass can eat larger BGs, therefore requiring less of them to be consumed daily. Is "Prey LEN" in the graph supposed to be Prey Length?


"In the age of information, ignorance is a choice." - Donny Miller
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jpsdad Offline OP
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Originally Posted by Steve_
So, by not harvesting 8-year-old Bass, you're hurting the growth of the rest of your Bass?

The way to look at it is this. At a given annual ladder rate the longer one allows them to grow the more bass one will be trying to carry. So if we are talking about a sustainable structure at a limited carrying capacity the extra maintenance comes at the expense of growth. An earlier harvest just leaves fewer fish to grow and so they have access to more prey due to reduced competition

Quote
I think there are a lot of variables that can't be plugged into an Excel Spreadsheet, such as the weight of each BG consumed. Larger bass can eat larger BGs, therefore requiring less of them to be consumed daily. Is "Prey LEN" in the graph supposed to be Prey Length?

The Prey LEN is the assumed mode of the "Prey Length". Mode is the most frequent size consumed and this according to the data accumulated from several DOW is about 18% the length of the LMB. So this column is calculated from the Geometrical Mean of the standard length over the growth period (one fall to the next). In nature, 95% of the realized prey as determined by evidence collected by the aforementioned reference fall between 10% and 25% of the length of LMB. Evidence suggests that only 2.5% of prey consumed exceeds 25% the length of LMB.

If you noticed the columns on the number of BG consumed, I estimated this number by dividing forage requirement total by the standard weight of BG at the estimated Mode of Prey Length. This is an estimate but it is a not a WAG it is a SWAG that probably isn't far from reality if the projected growth is realized. Take note of the stunted example. It suggests that a little over 3 daily are required for maintenance. If those 3 were 20% the length of the LMB, this would increase growth. The SS is very sensitive to LMB population and this factor drives growth and ultimate weight within the limitations of carrying capacity.

The scenarios demonstrate how limited recruitment must be to grow large fish. Because LMB eat prey that is proportional to their length/weight, and because growth rates are higher for small LMB, it is clear that even only 8 new 0-year LMB recruits will eat as many BG as all the other bass combined (in the 8 year example with 8 trophy path fish). Notice in every scenario, the consumption of BG/year is greatest for the smallest of LMB. So just one bumper crop of LMB YOY can completely destroy the food chain for trophies.

Last edited by jpsdad; 06/21/21 11:30 PM.

Common sense is not so common - Voltaire

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers


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As always, interesting & fact based analysis! But I recall Bob Lusk saying that he got a call about a pond that was not producing enough lunkers to suit anglers, even though they were assiduously harvesting LMB up to 4 lb. Bob told them that bass must get to 4 lb if they are to reach 8 or 10 lb. Very few YOY LMB ever reach 4 lb mark without being eaten or diseased along the way, so they shouldn't be harvested if trophies are desired.

Of course, so much depends on forage & fertility of the BOW, and even predation from cormorants, otters, herons, etc. Perhaps a lake absolutely loaded with big LMB might be enhanced by harvest of 4 to 6 lb fish. If so, I humbly volunteer my services! grin

Last edited by anthropic; 06/21/21 09:44 PM.

8ac, full 3/16. CNBG, RES, FHM 10/15; TP 5/16; FLMB 6/16. 100 12" NLMB & 1k GSH 10/17,L, 150# TP & 70 HSB 5/18. 1k PK 11/18. 100# TP 4/19, 200# RBT 12/19, 10k TFS 3/20, 100#TP 5/20, 25 HSB & 250 F1 9/20,L,180# RBT 12/20, 206, 7k TFS,100#TP 5/21, 225



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jpsdad Offline OP
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Yes, LMB can be overharvested. The criteria for the scenarios, however, was to harvest after time in pond. So a year marking system using fin clips identify whether a fish had put in its time and could be harvested.

In the example you reference, I am sure Lusk understood the standing population in order to make that recommendation. But for bass to recruit and replace 8 to 10 lb trophies (I mean sustainably) the number LMB must be quite limited and if there is substantial reproduction some approach to grow forage past the predation of smaller LMB must be implemented. For example, growing supplemental BG or TP or RBT to lengths that significantly reduce their consumption by <15" LMB.

Ideally, only LMB of the appropriate sex and of good genetics (growth and catchability) are recruited/laddered annually. If they are stocked as suggested, they can be marked and always released to live their prescribed length of life. Everything else can be relentlessly removed. If no recruitment except those which are stocked occurs, then there should be no issues with catchability or inefficiencies of forage use.

Last edited by jpsdad; 06/21/21 11:10 PM.

Common sense is not so common - Voltaire

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers



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