Pond Boss Forums Thread Like Summary - This paper is an absolute must read

The paper can be found HERE.

Escanaba lake is a lake in Wisconsin where DOW controls access and regress from the lake on a permit basis. Anglers check-in and on check-out are required to declare the results of fishing which includes both released and harvested fish. Fish measurements are taken. The DOW samples the lake and incorporates various accepted methods to estimate populations, natural mortality, exploitation mortality, and standing weights. It's a very interesting read.

In the county where the lake resided, a 22 in length limit for NP was enforced starting in 1964. Prior to that, there was no length limit for NP. The study reports the metrics prior to and following the regulation change. Results:

1. There was an increase in the biomass of NP and a corresponding decrease in harvested biomass. These more or less balanced. In other words, the biomass of NP increased by about the amount fisherman were no longer harvesting.

2. Growth, Condition, and average weights of NP declined as a result of the regulation.

3. Natural Mortality increased from 15% annually to 76% annually. Fishing Mortality decreased from 46% to 6% annually.

4. Although there were 47% more NP > 22" after the regulation was enacted, they were of lower RW and average weight. Ultimate weights were also lower. Ultimate weights were lower because growth rates were slower and the average weight attained at age declined.

5. Through much of the study, panfish populations were below detectable levels and crashed as a consequence of the regulation's effect of increased density of NP. It is interesting to also note that these decimated panfish populations still produced enough juvenile offspring to support remarkable weights of predators (NP, WE, SMB, LMB, and Muskies) ... but very few panfish reached adulthood. To give you an idea of how low the populations of panfish were ... the first documented reproduction of NP occurred in 1956 when harvestable adult panfish were very low. The reason for this was not stunting. WE effectively controlled recruitment so that few panfish survived to be adults. From there, additional year classes of NP recruited. The effect of this was to diminish WE populations and this resulted in panfish catch rates increasing during the early 1960's. During this "hey day" period of the early 1960's the panfish populations provided fishing catch rates of .04 to .06 fish/hour (on average it took 20 hours to catch one panfish of harvestable size). So mature panfish were not plentiful even when they were most abundant.

Aside from what there is to learn about the need to harvest predators in their 2nd or 3rd year of life to grow fish of larger ultimate weight ... the paper is a poignant reminder that the potential for predator biomass (limited by the production of consumable prey) is inversely related to the biomass of panfish brood. We shouldn't need a paper like this to be reminded of this principle. We've known about it for a very long time. We've known that the stocking biomass/density of brooders that produces the greatest number of offspring is small. 20 pairs/acre of BG averaging .5 lbs each (~20 lbs/acre of brooders) produces the greatest number of fingerlings. The more the brooders, the fewer the fingerlings. To be sure, consumable prey biomass and production can be the lion's share of the BG biomass potential or it may only be a minor fraction of it. In the case of Escanaba Lake during the 50s and 60s, the prey consumed annually by predator fish was significantly greater than the biomass of the forage brood fish, many times greater. Although, I would not recommend managing panfish brood at such minimal levels ... it is important to understand that it really isn't possible reduce consumable forage production by removing larger than optimum forage fish by fishing. Just as important, removing larger than optimum forage fish increases the production of consumable forage.

If a Pond can produce no more than it can maintain. Likewise, a pond can maintain what it produces.

If a Pond can produce a potential of P pounds in a year AND if B pounds of brood forage are present after 1 year, then the production of consumable forage is limited by the difference of the potential P and the brood weight.

Therefore, consumable potential can not exceed:

C = P - B

Consumable production is the sum of the standing weight of consumable prey and production of consumed prey for the previous 12 months.

Below is chart of this maximum plotted along two curves. Y=0 is the curve where all YOY production is consumed by predators. A balance below but near Y=0 is a balance that inhibits recruitment of the forage species and favors larger populations of LMB and LMB recruitment. Y=3 is the curve where the weight of consumable prey is three times the standing weight of the LMB. This inhibits LMB recruitment and favors small populations of fast growing LMB.




It is a lookback of maximum LMB consumption potential for the prior 12 months. SOOOOO ... this does not tell one the consumption potential for the next 12 months. So 1 year after stocking, if the proportion of brood weight were 50% of potential, then the forage consumption potential for the prior 12 months could have been no more than 50% of the potential. Furthermore, if it takes 5 lbs of forage to support 1 lb of LMB for a year, we can not expect the weight of LMB to exceed 10% of the potential. If the forage potential were 700 lbs and if the brood occupies 50% of that potential then ... the LMB weight can be no higher than 70 lbs. But the LMB standing weight can only be 70 lbs ... IF ... ALL consumable sized fish were consumed ... AND IF ... there was no mortality of brood in last 12 months ... AND IF ... there was no loss of forage production to predators other than LMB in the last 12 months. So the graph is an absolute maximum above which the pond cannot produce consumption as a proportion of potential and the appropriate expectation for 700 lbs of forage potential is that this mortality production will take a share of that absolute maximum reducing what was consumed looking back 12 months.


Consider a new 1 acre pond stocked April 1st with 1500 BG and stocked May 31st with 100 LMB where the first year survival is 80%. Consider it managed for 700 lbs forage potential and that the surviving brood achieve a biomass of 300 lbs one year after stocking (BG averaging 1/4 lb). This pond had a maximum consumption potential of 400 lbs looking back 12 months. And so if the maximum was a achieved where all the consumable forage produced was also consumed by the 1st year anniversary of stocking ... the remaining 80 LMB could weigh no more than 80 lbs (averaging no more than 1 lbs). This is pretty much what Swingle had in mind with his 40's era recommendation of 1500 BG/acre and 100 LMB/acre for fertilized ponds. There wouldn't be much recruitment of BG (overwintered YOY) and BG would grow to harvestable average weights of 1/4 lb in a year ... while average weights for the LMB would be around a 1 lb.

But can that biomass of LMB be sustained if there is an increase in the standing weight of BG? The answer is ... it depends ... on whether the forage potential increases sufficiently to offset the increase in Brood weight (or forage is supplemented). But on average, young ponds increase in potential by accumulating organics where the increase in potential is around 33 lbs/acre-year. But isn't it a tall order to ask 1200 BG averaging .25 lbs each to only grow .0275 lbs each? They have the capacity to grow, on average by .375 lbs each, at least in Dixie they do. They'll more than double in weight if they get enough to eat. The only reasonable assumption is that they will not cooperate with .0275 lbs of growth each. They each, will take whatever they can, and since they already occupy 300 lbs of the anticipated 733 lbs of potential ... they are going to have take their growth from the remaining 433 lbs of potential. Of course, they are going to have to compete with their offspring in the coming 12 months for food. And there will be a split. All will split it begrudgingly because they would like to eat/grow more but what can they do about it? There is only so much food to go around. The brood will take some and the consumable sizes will take the rest. See where this is headed my friends? One year from now, when we lookback we are going to find that the production of consumed forage will balance with the remaining potential not taken up the standing weight of forage fish which has grown. Since the consumption of forage will have fallen, so too will have the supported biomass of LMB. It depends on the mortality of LMB, the LMB still could have grown in their second season, but the fact remains, the biomass will balance to no more than 1 lb of LMB for every 5 lbs of BG consumed for the past 12 months. So in a case where the brood grow and average of .12 lbs (average weight of .37 lbs) and undergo 15% mortality over the subsequent 12 months ... the look back of consumption will be:

Max Consumption year 2 = 733 - Brood Biomass - Brood Mortality biomass - Consumable forage biomass

If the consumable forage is completely consumed such that the consumable forage biomass is zero at the 2nd of anniversary of stocking:

Max Consumption year 2 = 733 - 377.4 - 45 - 0 = 310 lbs of consumed forage

This consumption would have only supported 62 lbs of LMB. The LMB Biomass is lower because the consumption in support of it is lower.

The problem? A pond is a limited resource for the fish in it ... and the brood can grow into the potential that last year produced consumption. Just a gentle reminder, my friends, that it would be good to look ahead and manage against the trend of brood occupying increasing proportions of potential year after year. You'll see better growth of your brood fish, higher biomass of LMB supported, and you'll get to eat some tasty fish.

Planning a look forward isn't as straight forward as looking into the past with hindsight. But this idea of shaping the next annual lookback to have a supported a goaled biomass of LMB and brood, I think this is something we should all be eager to learn more about.

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Simply - a newly stocked pond reaches carrying capacity in 18-24 mths depending on water quality and location. From that point on (assuming no extraordinary event [feeding/fertilization] ) you are managing the relationship of and between the fish populations.

Bill, this is another strawman. I didn't say that. I noted that very small populations of forage brood can produce very large quantities of consumable forage for predators. I noted that after a minimum density is exceeded that there is an inverse relationship between brood biomass and consumable forage production. I explained why. There is limited weight of forage that can be supported/produced. If the water is supporting a larger weight of brood ... then it is producing a lower weight of consumed/consumable forage. One borrows from Peter to the benefit of Paul. In the end, the sum of the two is limited to the water's productivity ... it just cannot exceed that. So one cannot harm the production of YOY by removing a reasonable amount of brood fish and in principle ... it will increase the production of YOY. Likewise, one cannot increase forage production just by adding adult forage fish in waters where the resources are being utilized to their full extent. Not to say it may work if one expands the carry (like fertilization or feeding) ... it's just that it isn't necessary to increase forage production. If one expands the carry by fertilization or feeding, the production of YOY will increase for that reason alone. A bump in the forage brood isn't required but may be desired if needed for balance in support of growth of the panfish (eg when one doesn't want excessive YOY and over recruitment of the forage species).

All this is independent of what the species are. It just doesn't matter. The principle I have laid out is true for any sustainable combination of predator and prey. This is why people should take heed and learn this principle.