Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Getting started on a 50 acre unmanaged pond

Bill,

With regard to halving the LMB population or doubling the forage production, I was just wanting to describe two independent methods that lead to similar result in terms of individual LMB size. Although the LMB size limit expectation of either scenario would be roughly equal, the difference is the biomass of both LMB and the prey species. I saw two possible paths to increasing forage. One would be to add nutrients through feeding or fertilization the other would be to try to increase forage through manipulation of other fish species. I am very doubtful there would be any viable way to double forage fish production by manipulating numbers of other fish (e.g. carp or suckers). but where niches overlap between preferred prey species this may provide an additional boost of forage to support a larger standing weight of prey.

So one could push (feed and/or fertilize) or pull (remove predators and/or less desirable prey fish). Or combine the two methods. I did want to make the point that pushing will involve greater recruitment of all species ... where pulling will not greatly affect recruitment or total fish biomass.

You've already mentioned the complexity of food webs and so I do wonder how carp and suckers play into this. Most of the studies I have read peg estimates of these standing weights as small proportions of the total standing weights. BG usually rank highest at least in southern waters and in one Oklahoma study (where samples were taken by complete kill) the average of total rough fish (included carp, suckers, shiners, & shad) was small relative to average BG standing weights(about 1/3). But most of this standing weight in the average was from GZSHD. Carp, although they occurred in 26% of ponds only averaged 7% of the total standing weight compared with BG at 39%. Buck and Thoits found YP to yield a smaller but large proportion of BG standing weight in monocultures of the two species. Both prolifically reproduce and utilize broad food resources. But back to the rough fish. How would a reduction of clarity play into production of food for the YP and BG? Could an modest (not excessive) effect like this prevent deeper water weeds and shift primary production to phytoplankton? Benthic feeders are known to assist the recycling of nutrients oxygenating shallow sediment/detritus by foraging disturbance. So could they play a role in increasing food web production for species like YP and BG? One of the fascinating things about biological systems is that many propositions that are normally true also happen to be false ... depending on degree. So we can find circumstance where a proposition is just overdone and co-occurring effects destroy benefit. So perhaps one might seek to understand what a practical range that surrounds the sweet spot?

I am glad you mentioned the average LMB size mistickslinger is catching. I had overlooked this and was thinking they were smaller. I agree that's a decent size for LMB in unmanaged, un-harvested water. So that in and of itself is very promising. I'll start by saying that I think it means that a fair proportion of the LMB are being eaten as prey. How can I propose that? Well, because the OP isn't harvesting them and because they are 16-17 inches in length. This is where a frequency distribution would be helpful but if a 16.5" LMB represents the mean weight of LMB then at 80% RW the average individual weight is ~ 2 lbs. So we can make a rough estimate of number LMB by dividng the weight of the average fish by the LMB standing weight if we know it. It's unknown but I initially imagined a predator standing weight of 45 lbs and a gross standing weight of 300 lbs. So maybe this is a rough way to estimate numbers of harvest weight fish. Assuming 1 std-dev of a frequency distribution is limited to 15" to 18" LMB then we can make a rough estimate of the population for this size class is around 15 fish/acre ... or for the whole lake .... 750 LMB. So to me, If the lake supports 15% of its biomass in LMB the situation doesn't seem all that daunting. The OP mentions that catch rates are high and so I wonder if he could employ a slot between 15" and 18" harvesting 1/3 that number in the first year? This would reflect roughly 22% of the standing weight in the first year but might allow this size group (the first standard deviation) to grow from an average of 2 lbs to ~ 3 lbs"

The effect could possibly be better if the LMB could grow into adult prey fish that are presently just beyond their normally consumed sizes. IOWs there may be a reservoir of food that is currently unavailable that they could grow into. To be sure, all production of prey is determined by the annual mortality and if a broader proportion of the adult prey population is consumed ... this frees space for YOY and should actually increase the production of consumable prey.

IMHO, the enactment of such a slot would probably still require harvest of some of the then larger mean weight of LMB in the near term future years. IMHO a slot should be flexible and reflect the average weight ... they make sense where there is bottleneck greatly skewing frequency maximums at a less than desired size. I am not expert but I can definitely see the fish in the current prominent weights outgrowing the slot and still stunting there. So I do think that a slot, though it really makes sense currently must evolve where the goal is limited recruitment into the 16" class each year. If this can be achieved then the fishery can be catch and release for any tagged/fin clipped fish in this size class or larger and still allow for trophy collection near the ultimate anticipated size (eg > 7 lbs). Where the selected fish are caught by artificial bait, this can increase the likelihood that recruits will be susceptible to fishing and perhaps the cull can be focused on untagged/unfinclipped LMB that are caught with the assistance of live bait. Under such a regime, I see any unmarked fish as harvestable up to some goal proportion of the LMB carrying capacity. I am not sure what proportion is appropriate but I do know that production (weight gain) is proportional to mortality and that production/mortality can be as high as 30% of the standing weight and be sustainably replaced each year. Under a trophy path selection regime, the harvest of fish < 16" would become more prevalent than the harvest of >16" fish but one should not be shy to harvest unmarked > 16" fish if large LMB are desired. For such a regime, I like 1 fish per year for a carrying capacity of 45 lbs per acre. This translates to 0.0222 fish per total LMB carrying capacity and so would be 50 marked for trophy path each year in a 50 acre lake that could support 45 lbs/acre of LMB.

With regard to musky, I do recall the OP mentioning that pike once grew to 40" in the lake and fish this size wouldn't be shy to take LMB up to 12" and possibly larger. So the effect you mentioned may have on a smaller scale already been occurring. A harvest regime that allows Pike to reach 40" probably also allows 7 lb LMB. I don't really see 40" Pike competing with 7 lb LMB. My sense is that the prey that outgrows the 7lb LMB is readily available to a 15 lb pike. So it makes sense that if one can't grow 7lb LMB then he can't grow 15lb pike either. The pike must also be harvested and I think it possible that Sunil's idea of taking anything caught might limit the Pike to achieve this size. The pike should be a low percentage of the lake's standing weight possibly as low as 5 to 10 lbs per acre. That said, I think I would preserve fish over 34" in order to have fish in the lake that would cull LMB without competing heavily with LMB near the lake's ultimate weight.