Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Bream Size Distribution in Healthy Pond

Just how many there are is a mystery. There is no way to know the exact number without draining. Even so the exercise did open my eyes to means by which populations can be reasonably estimated and successfully managed.

First, the bass population contributes the most influence on BG size structure. Recruitment to the stocker size range of 3"-6" is very much dependent on the number of bass (LMB per carry capacity) between 8" and 15". Few are recruited to that intermediate size when the density of this range of sizes is high enough. Other factors contributing to recruitment of intermediate BG could be cover like submerged macrophytes or feed consuming predators. When LMB numbers are low, there is more recruitment to the 3"-6" range which is just what the big bass need. The standing weights of the 3"-6" are smaller than the standing weights of >6" BG even when they are numerous as they are big bass scenario. In fact, the bass populations need more than 3 times the standing weight in the first two tiers just to maintain their weight. This is possible because there are multiple BG cohorts. Every cohort of consumable prey produces more than twice the cohorts peak standing weight because they grow as they are being consumed.

I think we can all recall water that could be classified as Big Bass, Balanced, or Big BG. In some cases the water is completely unmanaged. So the populations are merely an artifact of its classification. Things we will never see are Big Bass waters where the LMB density per carry capacity is comparable to Big BG water. We are going to see skewing of populations that are consistent with the PSD ranges in the paper I referenced above. So in a pond where we frequently catch > 20" LMB ... we will never catch 10" LMB as frequently as we would in a big BG pond. The role of the keystone (the LMB) is very important and this ... presumably ... should be the easiest species to manage population wise.

After summarizing in the images above, one of the things that stood out was that the populations of BG exceeding 6" didn't differ a lot between the strategies ranging from 334 to 509.

The >6" BG also had similar standing weights. They ranged from ~157 lbs/acre for big bass to ~180 lbs for both of the other strategies. These should be peak standing weights at maintenance rations and so some form of harvest or natural mortality is required in order to keep individuals growing. 35% growth is easily doable for BG. So lets say we are going to take 25% and hope nature takes 10% of the biomass of >6". For Big BG (with the referenced PSD) the harvest number is 84 BG/acre for a peak carry of 305 lbs/acre. These are about equally split between 6"-8" and >8". So ... at the referenced BG PSD numbers ... this equates to harvest of 28 standard weight BG/Acre per 100 lbs of carry capacity.

Now lets suppose, that the BG are thin. They are 80 RW and I want them at 100. The PSD is the same. They are thin because the carry is supporting a larger number of individuals. In this case I would take 50% of the >6" population. 25% for overabundance evidenced by RW (1/.80 -1 = 25%). The other 25% is just the ordinary harvest figure. The remaining fish will now have twice as much food to eat from the harvest. To calculate the number ... I might start with the standard weight population of 334 and divide by .80 for the RW. The result is an estimate of 418 individuals per acre. 50% is 209 BG that I need to take out to meet growth and RW goals. Seem to high? Consider this. Taking only 84 where they are standard weight drops the population from 334 to 250. So the difference is 41 BG. So in a case where the >6" class may be over-recruiting (poor RW) this extra 41 is a very reasonable adjustment to compensate.

If the pond should support 250 lbs naturally and one is feeding enough to support 200 lbs more ... and the PSD is the same ... then the population should be proportionately higher consistent with increased carry and RW adjustments. For BG at 100 RW the harvest should be (28/100)*450 = 126 BG/acre and for BG at 80RW it would be 308 BG/Acre.

These harvest guidelines for a Big BG pond do not take into account recruitment in the 3"-6" sizes. It is possible that recruitment would be too low to support this harvest rate. Too many small LMB could prevent, for example, sufficient recruits to grow into >6" class as replacements. On the other hand, too few could lead to over recruitment of 3" to 6". If so, this class may also need to be thinned. Traps may be a better way to reduce the number of these sizes.