Over the past few weeks my lab mates and I have been slaving away spending hours in the lab processing data collected during the summer and banging our heads against the wall trying to write “R” code to help us analyze said data. At the end of this month we will be traveling to Savannah, Georgia to present our research at the annual meeting of the Southern Division of the American Fisheries Society. While preparing for this meeting I have spent a lot of time in the lab and not so much time in the field. All this time in the lab has really made me miss the good ole’ days of being sun burnt, bug bitten, covered in fish slime, and sitting on an aluminum boat for hours on end in the lovely humid Alabama summer. This being said, I have decided to spare you a lesson about pond management techniques and instead share a few pictures from this past summer sampling season.
Last summer was a highly productive summer and we look forward to more success this upcoming summer.
When managing fish populations we often become focused solely on the large sport fish and we forget what got them there. That 12 pound bass that you saw on TV that won that major FLW bass fishing tournament didn’t get that way from eating just fish, in fact the first couple months of its life were spent feeding on zooplankton. Zooplankton are microscopic bugs that juvenile bass rely on to give them the energy they need to grow big enough to start feeding on juvenile bluegill and other fishes. Considering my project is focused, in part, on evaluating growth of bluegill and largemouth bass you best bet your bottom dollar that we are monitoring the zooplankton densities in all of my ponds.
We sample zooplankton by dropping a zooplankton net twice the secchi depth (zooplankton are found between the surface and twice the secchi depth) and then slowly raising the net. We filter this sample using a 75 micron filter. Once the sample has been filtered we place it under a microscope and identify/count all of the zooplankton and measure the first 10 individuals of each species.
Counting/identifying/measuring one sample of zooplankton is very time consuming but interestingly enough, we are finding some rather cool results from our zooplankton analysis. Beginning in June we found that zooplankton densities in our shad ponds we drastically reduced when compared to the zooplankton densities in the non-shad ponds. This same trend has been observed in all of our samples through October.
So why is there a difference in zooplankton density and what impact does this have on the fish populations? There have been a number of studies that have shown that threadfin shad introductions are associated with drastic reductions in zooplankton densities. However, there are many factors that contribute to the density of zooplankton so we cannot conclusively say the threadfin shad are the sole culprits. As mentioned before, juvenile largemouth bass and bluegill rely on zooplankton early in life and without zooplankton juvenile survival would likely be very low. This being said, we might expect to see reduced bluegill recruitment (only the bluegill have spawned) when we sample the ponds again in the spring. From a management perspective, this reduced recruitment could be good or bad depending on your specific goals.
If you’ve been following my blog you probably know that one of the first things we had to do for my project was to completely remove the existing fish community in my five control ponds. The logical next step was to reestablish the ponds with largemouth bass, bluegill and threadfin shad. All of the ponds were stocked with largemouth bass and bluegill but only three of my control ponds were stocked with threadfin shad. By stocking threadfin shad into only three of my control ponds allows us to compare differences in bass and bluegill diets, growth, condition and recruitment as well as differences in zooplankton abundances.
A lot of thought and planning must go into stocking/reestablishing a pond. In fact, much of the early research here at Auburn was focused on stocking small ponds (i.e. what species to stock, when to stock them, and how many to stock). When preparing to stock fish it is important to take into account many different parameters such as: when the fish will spawn and when will they begin eating each other. Luckily for me, fisheries biologists have stocking largemouth bass, bluegill and threadfin shad ponds down to a science. Juvenile bluegill are stocked in the winter, threadfin shad are stocked in the spring and juvenile bass are stocked in the beginning of summer. This sequence of stocking is very important.
Bluegill are stocked in the winter at a rate of 1,500/acre. The purpose of stocking these bluegill is not to provide an immediate source of food for the bass. In fact, the majority of these bluegill will outgrow the gape size of the bass and will never be vulnerable to predation. The reason these bluegill are stocked before the bass is so they can spawn and produce juvenile bluegill which will provide food for the fingerling bass. As it turns out, largemouth bass transition from eating zooplankton (microscopic bugs) to piscivory (eating fish) right around the same time that the bluegill spawn. This is rather convenient because the largemouth are still very small (only a few inches in length) when they transition to piscivory and it just so happens that there is an abundance of tiny freshly spawned bluegill.
Threadfin shad are stocked in the spring at a rate of 900/acre. The idea behind stocking the shad is the same as stocking the bluegill. Stock the shad so they can spawn and provide the largemouth bass with a bunch of larval fish to eat when they transition to piscivory.
Largemouth bass are stocked in the summer at a rate of 75/acre. When bass are stocked they are generally only a few inches in length and are feeding primarily on macroinvertebrates and zooplankton. After a couple months the bass transition to piscivory and start feeding on larval bluegill and threadfin.
If you think back to your high school general biology class, you probably remember that the bottom of the food chain is almost always comprised of plants; ponds are no exception. In ponds, the bottom of the food chain is comprised of microscopic plants referred to as phytoplankton. When a pond is experiencing a phytoplankton bloom the pond will turn a greenish ‘pea soup’ color. This phytoplankton bloom may not be aesthetically pleasing to some people but it is very important for the ponds ecosystem. The amount of phytoplankton in a pond is commonly referred to as its productivity and is measured using a secchi disk. Ponds with a secchi below 24 inches are considered very productive.
All of the energy that fish eventually converted into length and weight, was first sunlight harnessed by plants and converted into glucose. This transfer of energy from the sun, to plants, to primary consumers, to secondary consumers is very inefficient; in fact it is estimated that only ten percent of the net production of energy at one trophic level is converted into net production of energy at the next trophic level. What does that even mean? Basically for a bass to add one pound of weight it must consume 10 pounds of bluegill who must consume 100 pounds of zooplankton. This is why you generally see larger fish in more productive bodies of water.
When a pond owner wants big fish, we as managers try to keep the pond highly productive (secchi depth between 18-24 inches). Plants need two things: sunlight and nutrients. In ponds nutrients are generally the limiting factor in plant growth, and that’s where fertilizer comes into play. Most fertilizers are comprised of Nitrogen (N), Phosphorous (P), and Potassium (K) and come in liquid, granular, and powder forms. For my north Auburn control ponds, Southeastern Pond Management donated two years worth of their SportMax Pond Fertilizer. This fertilizer is 10% Nitrogen, 52% Phosphorous, and 4% Potassium (10-52-4).
Following the recommended fertilizing rate can greatly enhance the productivity of the pond, however; adding too much fertilizer or fertilizing randomly can be very detrimental to the pond. For example, if a pond is over fertilized the phytoplankton will become extremely dense. During the day when the phytoplankton are photosynthesizing (taking in carbon dioxide and giving off oxygen) the dissolved oxygen will increase, however; at night when the phytoplankton revert to cellular respiration (taking in oxygen and giving off carbon dioxide) the dissolved oxygen plummets which can put immense stress on the fish. Additionally, a few days of clouds can lead to a phytoplankton die-off which results in very low levels of dissolved oxygen. If the dissolved oxygen in the pond drops below 2 mg/L most fish will die. The moral of the story is fertilizer has great potential to enhance the productivity of a pond if applied according to recommended rates.
One of the many differences between managing a small impoundment and managing a major reservoir is the ability to control almost all aspects of the pond (i.e. nutrient levels, structure, aquatic vegetation, fish community etc.). This high level of control allows managers to efficiently create a system that meets pond owner goals such as big bass. One of the most important aspects of pond management is controlling water quality. The quality of water in a pond can be a major contributing factor to the success or failure of any pond. Before establishing a pond it is very important to evaluate the water in your pond. There are a few cheap and easy test you can perform that will provide you with invaluable information about your pond water. These tests include alkalinity, hardness, and soil.
Alkalinity can be defined as a measure of the waters capacity to buffer (neutralize) acids. The units of Alkalinity are in parts per million (ppm) and indicate the quantity of titrateable bases (i.e. bicrabonates, carbonates, and hydroxides). These titrateable bases buffer acids and help the pond maintain a fairly stable pH throughout the day. Having an alkalinity above 24 ppm is important because an alkalinity below that level increases the risk of large swings in pH which can lead to a fish kill. Hardness is a measure of the concentration of divalent salts (i.e. calcium, magnesium, iron, etc.) in the water. The units of Hardness are in milligrams per liter (mg/L). These divalent salts are very important as fish use these salts for metabolic reactions, bone formation and blood clotting.
Taking a sample of your pond soil to a lab and getting it tested can give you insight about the acidity (pH) and composition of your soil (i.e. Phosphorous, Potassium, Magnesium, and Calcium). Soil tests are used primarily to determine the proper about of lime that should be added to a pond to prevent large swings in pH.
If pond soil is too acidic and Alkalinity is low, the pond will experience swings in pH throughout the day which can greatly stress the fish in the pond. Stressed fish tend to to have poor growth rates as a result of death. We don’t want all of our fish to be stressed and die so as managers we must mitigate these swings in pH as much as possible. The way we stabilize the fluctuations in pH is by adding appropriate amounts of agricultural lime. Agricultural lime is alkaline which means it efficiently buffers acids and mitigates swings in pH.
This past fall I went out and tested the alkalinity, hardness and soil for all of my control ponds. After determining all of the ponds needed lime, we ordered 120 tons of agricultural lime, constructed a liming barge (basically a pontoon boat with a wooden deck), and tracked down a 4 inch water pump. The ultimate goal of spreading lime is to spread it evenly across the pond bottom. The most efficient way of doing this is dumping the lime next to the pond bank, using a front loader to load a couple hundred pounds of lime onto the pontoon boat and then using the 4 inch water pump to blast the lime off the pontoon boat.
If you still have questions about alkalinity, hardness or liming ponds, the following links are great resources:
It’s spring which means it’s time to put away the coat and gloves and grab a fishing rod! What a better way to get back into the swing of spending time outside and catching fish then a fishing tournament? This year I put the shad research on hold for a couple of days and helped organize the annual David Partridge Memorial Big Bass Tournament which was held on June 26.
The tournament took place on a few of the ponds at the E. W. Shell Fisheries Center, North Auburn Unit and is in memory of David Guy Partridge, who received his masters in fisheries from Auburn University in 1997. David worked for the Georgia Department of Natural Resources for 10 years until he lost his life in a car accident.
Proceeds from the tournament go to the David Partridge Memorial Endowment at Auburn University, which provides funding for an annual award for a graduate student studying the conservation and management of recreational fisheries.
The close to 100 anglers who participated in the tournament came in all shapes and sizes and fished for everything from crappie to largemouth bass. The biggest bass caught was over 8 pounds and was caught by an angler fishing for crappie from the bank (see you don’t need a $20,000 bass boat to win tournaments).
As good fisheries students, we made sure we kept track of harvest on all of the ponds. Harvest is a very important component of pond management and is a very effective pond management practice. When ponds become over populated with largemouth bass, the bass begin to compete with each other for resources which ultimately results in a high density of small bass (commonly known as “bass crowded”). To curve this bass crowding, it is recommended that 25 lbs./acre of largemouth bass are removed each year (this rate varies with pond productivity). Removing bass lowers competition for resources and allows bass to add weight and length more efficiently.
Whenever you drain a pond you tend to find a lot of surprises. Some surprises are pleasant like finding a bunch of new fishing tackle. However, some surprises are not so pleasant like finding an entire forest of small trees and shrubs covering the entire bottom of your pond, this what we found in S-16.
When S-16 was first created it was a modest 2.48 acre pond but after a few years of existence, it was converted into a 10 acre reservoir. As the water level rose from the 2.48 acre pond to the 10 acre reservoir it backed up the tributary creek and eventually flooded a forest full of small trees and shrubs. After years of being underwater, the portion of the trees above the water broke off and left only the lower portion of the tree. The lower portion of the trees hardened and created thousands of perfectly submerged lower unit/propeller destroyers. The biggest concern with this submerged timber was it provides excellent habitat for Largemouth bass in the MIDDLE of the pond which means the Threadfin shad have no pelagic refuge. When Threadfin shad are stocked into ponds with no pelagic refuge and a Largemouth bass population, the Threadfin shad generally do not last very long due to predation. Additionally, the trees were releasing a lot of tannic acid into the water which was inhibiting our ability to establish an algal bloom (algal blooms are very important in proper pond management). Long story short, the trees had to go.
When you’re standing knee deep in mud in the middle of 7 acres of trees and shrubs that have to remove, you start to get a lot of ideas about how to remove said trees and shrubs. The first idea that came to mind was to just get a bulldozer out there and completely bulldoze the entire bottom of the pond. Unfortunately bulldozers tend to become utterly useless when they sink several feet deep in mud and can’t move. This being said, the Bulldozer option was out the window. The next idea that came to mind was to burn it! After 2 full days of cutting/stacking timber, and monitoring a bon fire that was big enough to be seen from space, we had removed an infinitesimally small portion of the standing timber and it was back to the drawing board to find a more efficient method.
After reevaluating the task at hand, it was decided that we needed to hire someone who is an expert in brush removal. Luckily Auburn has a lot of connections and was able to set us up with someone who clears brush for a living. At the rate we were clearing the trees and shrubs, we estimated it would take several months to completely clean the bottom of the pond. Our hired brush removal expert had the entire pond bottom cleared in a half day (including a lunch break). As it turns out, a bobcat with a Forestry Cutter Package equipped with a spinning drum full of double-tipped, carbide cutting teeth can clear thick trees and brush as easy as mowing the lawn.
Once all of the brush was cleared we were able to get an excavator in there and knock over a bunch of large dead pine trees that lined one of the banks.
Now that we have removed almost all of the timber, the Threadfin shad will have a large pelagic zone to seek refuge in, we wont have to worry about destroying any lower units on our boats (knock on wood), and we should be able to establish an algal bloom now that we don’t have a problem with the tannic acid.