OK so you can find the Swingle paper on fish production
here.
Anyone inclined to read this paper will soon make the connection that the production system described in my initial post was inspired by none other than Swingle himself. If one digs into to the SS again, he will notice a number in the lower left that holds the spring standing weight. He will also notice just how small the number is (32 lbs per acre). This weight represents the goal for standing weight after harvesting the prior years production. You will also notice column G, which is the goal for the standing weight of Crappie in the Fall after spring weight fish have grown a season. You might ask how can the weight of crappie more than quintuple in a single season? The answer is that ... thanks to the harvest ... in the Spring the BOW is no where near its carrying capacity. Prey organisms like Daphnia, insects, shrimp, and gambusia are free to flourish and proliferate. They bind the excess energy that the greatly reduced (by harvest) biomass of crappie cannot consume early in the season. As the crappie grow they consume more and more of them. Even so, because the crappie standing weight was initially very low, the crappie could only eat so many and it was this limited predation that allows prey organisms to proliferate and produce food that will be later utilized by the crappie.
NOW STOP. What did the harvest do? In a sense it made the BOW a second year BOW again. This kind of intense harvest is able to sustain a BOW's youth. How does one kill this production system? He begins by noticing the relative weights are off the charts and begins to imagine the Fall crop of crappie will double their weight next year and foregoes a harvest. To find out what happens when one does this all you have to do is change the 10 to 400 in Row 5 column C. If you look at the forage requirement to grow 400 crappie from 8.3 inches to 10.1 inches (.28 lbs per crappie) you will find the forage requirement just for this year class is 1680 lbs.
What makes this untenable, is that that when crappie attain a length of 8", they transition from primarily invertebrates to a diet increasingly dependent on fish prey. Their success in reproduction is linked to the abundance of fish prey as well. They just quit desiring invertebrates as much and put increasing effort into feeding on fish. Come Spring the BOW is loaded with fish that are hungry. They greatly restrict the abundance that their prey can achieve in the coming growing season. In the fall, instead of a BOW full of 10" and 8" fish, the result is more dismal. Last years 8 inchers may have only achieved 8.5 inches, last years 4.4 inchers may have only achieved 6 inches and the current year's YOY don't make 4". Anyway, one can clearly understand how the production swiftly declines and nothing grows until some of them begin to starve to death or begin dying of old age.
A bow is rejuvenated by harvest. For crappie, they can reach a harvest size by end of their second year of life. If the harvest focuses on this year class then production can be maximized. Look guys, 124 lbs per acre is a doable harvest in a 1 acre bow and many BOWs could outperform this.
Lets take a look at predators now. The last three year classes are crappie that are consuming mostly fish. The plan greatly limits their abundance by harvesting the year 1 class yet they still comprise almost two thirds the Spring standing weight of about 18 lbs per acre. The final 3 classes have a forage requirement of 198 lbs/acre. This forage requirement could be provided both by crappie YOY and supplemented by another non-competing prey species like gambusia. Two things can break the system. Insufficient harvest of 1 year crappie and/or too much recruitment of O year fish. For the latter, an increase in the biomass of predators is called for, for the former, predators capable of cropping the harvest deficiency is indicated. One knows these are problems when year 1 and year 2 fish do not make their length/weight milestones.
