Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Managing black crappie

MnAngler,

After re-reading your last post I would like to comment on a couple of things. You said:


Just so that you understand, I didn't pluck any numbers out of thin air. All numbers were provided by you and I just did some analysis with your numbers. Nothing else. "My numbers" are "your numbers" expressed in a different format. To get good advice on balance, it is important to have an accurate understanding of populations. Your inch ranges have moved around a lot and I think you are trying to rely on memory of a very limited sampling. No fault there, I know you are trying to provide an accurate picture. I would just say, that if you aren't providing accurate information, the analysis will also reflect the same inaccuracy. If you are serious about managing this BOW at its peak performance, you will need a very accurate understanding of population proportions. At the very least, length measurements. I could work with length measurements and a gross weight too. But we need good data, not memory, if we are to truly do good analysis and make effective recommendations. Furthermore, good data on all species is really important. Good observations on year class recruitment or recruitment failure is also important.

I mentioned earlier that there is a food limitation. Your observations are evidence of that. Lets say your crappie are 70 RW (just hypothetically), what this means is that last year they were missing 30% of what they needed for maintenance at 100 RW. Give or take 3% or so. Let's say your pond produces the food required to support 150 lbs/crappie of crappie (just hypothetically). The support they need (in Minnesota) adds up to around 0.8 lbs of ingested animal dry matter. So around 120 lbs/acre. If they weigh 150 lbs/acre, you can rest assured they are getting it. But they needed (120/0.70=171 lbs) of animal dry matter. They get their ration from various pond organisms with various % dry matter content. The weighted average of that consumption would tell you the total weight of what they were eating. But lets just use shiners as an example. They are about 25% dry matter. So the difference of what they needed to be 100 RW is (51 x 4~200 lbs) of live shiners for each and every acre. Around a 4400 lbs shortfall of shiner forage overall for the BOW. If one didn't mind paying that every year then one could increase the carry capacity and fatten the hypothetical 150 lbs to 215 lbs. Now each and every year there after one would need to supplement the same 4400 lbs of shiners to maintain the same 215 carry capacity. Growth after the initial year will still depend on mortality. What ever (reasonable <50%) percent of the biomass dies, that percent will be replaced to fill the carry capacity. For BOWs that have reached carry capacity, highest growth will always be associated with the highest mortality. This is an immutable law that cannot be sidestepped without unlimited food supplementation (something that will lead to mass mortality anyway).

What is wrong with the BOW isn't really a food limitation. The condition of the BCP reflects the balance of food and the population numbers. There are too many BCP in the larger sizes to be supported in good condition. Their biomass at 100 RW requires more maintenance than the BOW can provide. Now it may well be producing a lot of food. Consider what 150 lbs of crappie need in terms of equivalent shiner consumption. Around 480 lbs equivalent or 9600 lbs of shiner equivalent produced annually. How much value is there(maybe $96,000)? All you have to do is bring your population into balance with this valuable natural production of food and the size and condition will be good. Mortality is the key to growth. You need to harvest a minimum of 20% of the biomass of > 8" BCP standing weight each year. Because it has been neglected for years, I recommended 37.5% this year. I don't think I would go beyond that number and would probably ease it back to 20 - 25% next year and following years.

There are ways to estimate population numbers (and biomass)from marking and recapture. I don't know how deep you want to go down the rabbit hole. Given the size of the BOW and the potential quantity of fish needing harvest, I think your plate is pretty full even getting close to the harvest needed. Whatever you do on that front should benefit the fish remaining even if you don't notice it by casual observation.