Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations When and what to start harvesting LMB

Ken, if you have other ponds you can use as grow-out ponds, I would grow bluegill, fatheads, and GSH in some of those ponds.

The harvest started this morning. My 82 year old neighbor and I caught a few, including a 18 inch at 4 lbs 3 oz. Kept a 16 and 14 incher. Early released a couple of other big ones.

Caught about 20 CNBG, RES and GSF. Biggest was about 4.5"

Nice!!!!

Who knew doing hard work to improve your pond could be so much fun?

Gunboss,

Good to see you getting started. You should probably get a good census of the LMB population. I was and still remain uncertain of the population of your initial stockers and recruits. In a young lake like yours the intial stocking can comprise a large proportion of the lake's LMB biomass and because of how good the fishing was for > 5 lb LMB I suspected (maybe incorrectly) that you had good survival of the initial stockers and that recruitment was muted. I ran several natural mortality assumptions (ranging from 15% to 30%) for the year class which yielded survival ranging from 7.23 LMB/ACRE to 19.08 LMB/ACRE. I leaned toward the 19 because you described fishing that was in the neighborhood of on 1 >5 lb LMB/hour and I know that's a remarkably good number for that size fish. Could, however, the mortality have been average (30%) where ~3.5 female fish per acre > 5lbs could provide that level of fishing? IOWs should I have used higher mortality instead?

The spreadsheet below depicts year by year growth of the initial stockers under the assumption of 15% natural mortality. We are presently at the end of year 5. One thing that gave me pause is the forage requirement of 662 lbs BG for just the initial stockers. Now with males half the weight as females that falls to 75% or 496 lb BG. With males undergoing more mortality than the girls that number could be reduced further into range that is doable for a very productive system. But if this were the case, it wouldn't leave much room for recruits which is something I was concerned about. What is the real number of survivors per acre? And what is the population of recruits? To be or not to be ... so to speak. If the survival was that good I am probably correct for suspecting very subdued recruitment. But the survival may not have been that good (and probably wasn't).



OTOH. With mortality average (30%) this makes room for somewhere in the neighborhood of 30 lbs/acre of recruits ... possibly up to 40 lbs/acre. In this later case, you don't have to harvest the >5 lb fish since they will be dropping off at around 1.5 to 2 per acre per year naturally. Whether you would harvest any of these large fish would depend on whether you think the harvest would increase total mortality or not. Some may argue that taking some would prevent some natural mortality (thus not affect the total mortality by much if any). For the most part, fish that large use most of their consumption to support metabolism and only a small part of the consumption actually grows the fish. This I think is why mortality averages 30% to begin with. LMB swiftly fill carrying capacity and so continued growth depends on mortality. This mortality is facilitated by the summer growth each year which grows the standing weight to a level where there is insufficient forage for maintainence. The strongest competitors are maintained but on average 30% die because they decline and become more susceptable to disease and other causes of natural mortality.

You expressed an interest in managing the water according to Richard Andersons PSD. Below is spreadsheet working with Willis' recommendation for the number >15" fish and Anderson's PSD recommendations for the other size classes in relation to the >15" population. I used the assumption of 30% mortality. Because of mortality, the <12" cannot be equal to the 12"-15" population (eg some of the < 12" will die of natural causes) but the population ratio for > 15" is very close including 30% average mortality. It estimates an annual harvest of 193 LMB in the 12-15" range leaving 2.34 LMB/AC (82 fish per year) to grow to trophy size. This should put you in place that is similar to where you are now. ~ 7 fish > 15" but where they are spread across multiple year classes as opposed to concentrated in the year class of initial stockers. The fishing should be similar to what you experience now but where ultimate weights and ultimate weights could be larger.



Caveats:

1. Only 82 fish per year should be allowed to grow from 12"-15" to > 15". These should be marked so they can be released when you catch them in the future.

2. The scenario depends on the recruitment of 16 LMB/ACRE into the 8"-12" class. If the recruitment to this size class is less ... then the harvest of 12"-15" must be reduced in order for sufficient recruitment into the >15" class. This is why I recommend marking trophy track recruits. OTOH, if recruitment into the 8"-12" class exceeds 16/Acre then some harvest of 8"-12" would be required.

3. If you are unable to mark 82 females in the 12"-15" class annually ... by this I mean that they just are not there to catch and mark ... then the >15" class may be under represented. This would be a case where recruitment is too subdued to maintain population numbers. This can occur where BG populations are dense and individuals are of smaller size. It tends to be less common on an ongoing basis but stocking a pond for trophy production is essentially setting the stage for this to happen in the early stages. If recruitment into the >15" size is underrepresented, then it will take more fishing effort to catch this class of fish but the ultimate weights achieved should be larger.

4. The scenario requires the production of 390 lbs of BG forage in the sizes the LMB need. This is in addition to the parental stock. To produce this much forage will require multiple spawns. If less forage is produced, the ultimate weight and growth will be reduced to balance the forage production.

Practical considerations:

1. The two size classes less than 15" in length consume 55% of the BG prey production. These populations could be reduced to allow more forage for >15" LMB. This would come at the expense of BG size. Given that BG are already small, this may indicate that the populations of less than 15" LMB are underrepresented.

2. The only way to be sure you have enough fish growing over >15" is to mark them and keep records.

3. The only way to be sure that you don't have too many fish >15" is to harvest unmarked fish >15"

4 The simulation assumes an instantaneous reduction by fishing of 12"-15" fish in the autumn each year. IOWs. These fish are allowed to grow all summer and thus are maintained and grown by in pond consumption which is the greatest of all size classes. To whatever extent some of this harvest mortality occurs before the end of the growing season ... less forage will be consumed by this year class and more forage will be available for all remaining fish > 12".

5. Supplementation of BG at the appropriate forage size could help maintain and boost forage production to the levels required. These should be stocked at around 3 inches in length if needed. In this size, they will benefit mostly > 15" LMB and to a much lesser degree 12"-15" LMB. Since 12"-15" consume in lake production at smaller sizes than >15" have much interest ... this is OK. They should get enough to eat provided they are not too numerous.