Were the fingerlings year 1 or year 0, I am leaning year 1, what are your thoughts? The minnow numbers are by the acre?
Here are some interesting facts you might like to chew on. Swingle found the presence of Gambusia Increased BG production by 149 lbs/acre in fertilized ponds. The stocking rates were ~1500 BG/acre and 2 lbs of Gams. He also found that FHM increased total production by 179 lbs/acre to a LMB/BG combination. In the reference, the entire LMB-BG biomass were totaled in combination and not severally, so I cannot tell you how big the LMB were able to grow but the regime was a December stocking of 3lbs/acre FHM and May stocking of LMB (54/acre) and BG (~1500/acre). Both examples had total harvest in the mid to late fall period where the standing weights were almost completely comprised of the BG and LMB-BG respectively (minnows essentially eliminated). Given that the LMB-BG-FHM combo produced 108 lbs/acre more than the BG-GAM combo, The increase in production was a combination ... probably ... shared between the BG and LMB.
The increase in production for the Gam example was 89% while the increase in production for the FHM example was 66%. It may interest you to know that in the GAM treatments that the BG were able to attain an average weight of .20 lbs/individual. If we take the rate of growth for males is to be twice that of females in first 18 months, I estimate the males were primarily in the 6.5 to 7.0" lengths and the females were primarily in the 5.75 to 6.25" lengths ... PROVIDED the BG didn't recruit much. It may be that they didn't not reproduce a lot given the stocking rate, (Swingle studied the populations required to inhibit or eliminate recruitment and exploited that to increase production of harvestable fish).
OK. so with this background I am wondering why such a large stocking rate of BG doesn't increase the BG competition for FHM compromising the growth of the LMB fingerlings. The only conclusion that I can come to is that the effect is counterintuitive and might reduce competition for FHM/GSH by the BG. It is clear that tripling the stocking rate of the BG will decrease the growth of BG by at least 67%. So perhaps, the BG don't compete as much for minnows when the stocking rates are increased from say 500 BG/acre to 1500 BG/acre because BG development is delayed sufficiently to allow the LMB longer access to the FHM (thus more FHM food) than they would have had with the reduced number of BG.
To be sure, the BG are too large at the time of stocking to be food for the 3" LMB fingerlings. Furthermore, at that stocking rate. It is unclear just how much food the BG YOY might contribute to forage. To be sure, fingerling BG would need a minimum of 6 to 8 weeks to begin reproduction and another 8 weeks to recruit YOY in the 2" sizes. A lot of research supports that BG fail to recruit at such density. Whatever is happening in this first year example, it may not be as simple as the LMB are eating three times the BG YOY (1500 BG/AC vs 500 BG/AC).
The things I think contributed most to that stellar 1st year growth in order of importance are:
1. Lower LMB stocking rate (50/Acre vs 100/Acre). The difference between a 12" LMB and a 7" LMB is enormous. The 12" LMB weighs 5.6 times more than the 7" LMB. Huge difference. So in otherwise equal conditions, you have witnessed only 18% the LMB production when increasing the stocking rate from 50 to 100/acre. There is a very good reason for this. The doubling of encounter limits the time that forage can grow and put on weight. The resource is rapidly diminished emphasizing the actual limitations of available forage. In essence, the forage days are reduced 5 fold by doubling the LMB stocking rate. I've recently be working with simulations of forage consumption and have found that the balance is tipped by very modest increases in predator numbers.
2. Delayed development of the BG (due to greater stocking rate) which delays competition for the FHM resources at least for the first couple of months of the 4.5 month growth window cited.
3. Feeding. This will of course increase growth of the appropriate sized prey if eaten directly or from manuring effects.
So I do think that LMB growth was mostly factor of the LMB stocking rate and less to do with the rate of BG stocking. By using a 30 to 1 ratio, one essentially reduces the number of LMB stocked. The important number is the 1 (as opposed to the 30) and so the LMB stocking rate then becomes what is one's limit to spend on BG ... perhaps $750 per acre where one can expect growth to harvestable sizes in one season. Such a combination probably maximizes the quantity of harvestable BG while allowing substantial growth for the LMB in the first year.
