TyW - In this post I will address some more of your concerns you have raised about growing larger bgills and stocking your gravel pit pond.
Growing Bluegills. Here are just a few of my rarely mentioned ideas about growing larger sized bgill in your particular pond setting. These ideas are additional to the traditional ways of growing large bgill. Firstly, I think you should make sure your bgill stockers come from brood stock that have proven genetic propensity to attain large size. This minimizes the variables that can be responsible for poor growth. Then if your bgill are not growing rapidly or are not attaining the target sizes in the expected amount of time, you can right away eliminate genetics as a problem and look to ecological problems and solutions. Eliminating variables is important in trouble-shooting problems of fish growth.
If you cannot locate a reliable source for high quality, good, brood stock fingerlings then produce your own fingerlings. Go to a local lake with a reputation for producing trophy bgill. Catch and transport about 15 adult pairs to your pond. This should produce more than enough fingerlings. In reality the percentage survival and number of fingerling produced from 4 or 5 paired bgill would be more than adequate for a pond of your size due the pond�s abundant, virgin food reserves and minimal amount of initial competition from older year class bgill. The hazard of using this method and your likely problem then would be to adequately get the bgill fingerlings cropped so stunting does not occur in the first year class. This would involve proper timing of stocking the LMB fingerlings. Another disadvantage of this method of adult stocking to produce fingerlings is it sets the pond fishery back about one year in its development while you wait for the hatchlings to grow to a size of those what would have been stocked the �traditional� way i.e. buying fingerlings or juveniles and initially stocking them.
Secondly, for growing big bgill, I think, but do not have not real proof or data, that it is important to construct the pond so spawning areas are limited and not over sized which has some impact on the number that are hatched and ultimately can have an impact on and can affect hatchling survival and reduce the chance of overabundant year classes of bgill. In most traditional management methods control of YOY and overabundant year classes of panfish are done with predator manipulation. I contend that if spawning is curtailed somewhat, or controlled, the management of predators becomes an easier task and this will ultimately result in faster bgill growth due to a more controlled system. The more variables you have to deal with, the more complex or difficult fish management becomes. Fish management is all about control and the more control you have the better the fish will grow. Limiting spawning areas may not be a major cause of better bgill growth but I think it contributes. Your task to effectively grow large bgill, will be to correctly match the number of consumers (bgill) to the amount of food reserves � i.e. maintain proper balance to achieve optimum growth.
Supplimental Zooplankton Stocking - D.magna, because they are large and relatively slow swimmers, will not have long term survival as a viable population in the presence of facultative, planktivours grazers such as bgill or yellow perch that often select plankters on the basis of size. It has been found that these types of fish can actively search for and visually select each plankter they injest. Bgill can also gulp water to filter zooplankton while swimming. Stocking D.magna is sort or like stocking fatheads with LMB. Okay for a jump start on growth but long term survival is not likely and futile. I have done stockings of large daphnid types numerous times. Basically what happens is planktivorous bgill selectively consume the largest zooplanker possible within their physical and behaviorial capabilities and abundance of prey. Large Daphnia are first to be selectively grazed esp during periods when macroinvertebrate densities are low i.e. cold periods. Cyprinid fish when abundant can also regulate the size and species composition of zooplankters. Extent of weed bed coverage and type of vegetation can also have a direct impact of zooplankton composition and survival.
If you are serious about optimizing this zooplankton food base and want to try D.magna, I recommend that you introduce the D.magna early in the pond filling process. If possible do this 2-4 months before fingerling fish are introduced. Meanwhile locate some healthy zooplankton communities in lakes or ponds near you. Do this by quizzing the local academic limnologists or search out zooplankton communities on your own. Start your elimination process by selecting lakes (usually clear water types) with known or good populations of large or trophy bgill. Obviously something is working in these lake and if you are lucky it is related to plankton composition. Collect zooplankters with vertical net tows (64 �100um mesh) that start at or above the thermocline if a thermocline is present. You are looking primarily for larger forms of Daphnids, Cyclopoids and Calanoids that are 1.2 to 1.8mm long. It is doubtful that some of the larger (2-3mm), deep-water taxa, such as Senecella, Limnocalanus, Epischura, or Mysis (15-20mm) will survive in your pond. You will need at least a dissection microscope or simple compound scope, which you should have access to at school, to verify general zooplankton types in your search for the proper brood stock site. Another thing to keep in mind is to not collect zooplankton from lakes or ponds with known bluegreen algae blooms. You may have to do a small sampling survey to get this knowledge. I think it is bad practice to introduce this problematic bluegreen algae �seed� into your pond. Once you locate a good source for brood stock, then make several vertical tows from deep water locations. This should provide you all the plankters you need for seed. Best time to introduce your collected �seed� is up for debate. I think it should be done when your YOY bgill are big enough to eat D. magna because these largest forms will now start to be cropped heavily and daphnia inter and intra specific competition will decrease thus making �room� for the �seeded organisms� to flourish. I think biodiversity of the zooplankton community and optimum sizes of zooplankters are two of numerous important factors in growing large bgill on natural food sources.
Other Invertebrate Taxa . I would definitely explore stocking some of the amphipod taxa. The deep-water, benthic & planktonic, Pontoporeia will probably not survive in your pond but if you have some littoral vegetated areas other scuds such as Hyalella and Gammarus are good potential taxa. They should be available locally in your area and you can collect them on your own or buy the larger forms from reatailers. Habitat needs to be correct for optimum survival and perpetuation of several of the taxa.
Optimizing Littoral Zones . I recommend that if your pond will have lots of steep sides and minimal areas for colonization of extensive weedy beds, then have the construction crew create a few earthen fingers that descend from shallow water to deeper areas. Construction of underwater humps when vegetated are also excellent fish attractors, serve as small refuge areas and are very good food producing areas for bgill. Keep in mind the general rule is that 90% of the catchable fish are concentrated in 10% of the water. Knowing where that 10% is located will be key to harvesting your fishery. Under water vegetation will easily grow to depths of 6-8ft and maybe grow sparsely to depths of 13ft in clearer, nutrient poorer water like your gravel pit pond should have in WI. These fingers and humps can take the place of and be better food producers than lots of manmade structure. You may not have time or energy to install lots of the artificial structure before the pond fills.
Stocking Suckers. I think stocking suckers as a forage fish for a few musky is not a good idea in your particular situation. Here is why. 1. White suckers can live a relatively long time (14-17yrs) and will grow fast in your food rich, new, pond setting due primarily to little interspecies competition. Three yr old suckers can easily be 15� long. Only musky 34� and larger will likely prey on these fish. Growth of the suckers could outpace growth of the musky�s ability to eat them. Surviving suckers can easily grow to 25� (6-7lbs). 2. I assume that you do not plan on cleaning these fish for table use. And as they grow beyond 15� �16� they are consuming lots of valuable, protein rich benthic invertebrates such as Hexagenia and midge larvae that could be otherwise used to grow large bgill, your primary goal fish. With an aging population of white suckers, you are tying up valuable and limited pond productivity in an unharvestable, unusable, and nonproductive fish biomass. I think that the few musky that you are planning to stock, would grow quite adequately on prey of LMB, bgill and an occasional walleye (if stocked).
Walleyes - Since you are in �walleye country� I would not hesitate stocking some walleye into your pond when you stock the LMB fingerlings. You can enjoy them and learn about their habits in a pond until they �run their course� in about 8-12 yrs, providing you do not supplement their numbers. I �think� walleye will feed on LMB almost as often as bgill due to walleye�s foraging habits, foraging efficiency and the body shape of bass compared to bgill. And walleye may even provide you help in thinning the bass population from 15 ac of water so bass do not become over abundant. However overabundant bass would not be all bad if you are trying to grow trophy bgill.
I have rambled enough for today. I will return in a day or two after I organize and compose my ideas about what I think are several options for the harvest of bgill from your gravel pit pond.
