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    Fertilizing Your Fishery

    by: SOLitude Lake Management   |   May 06, 2019

    SOLitude Lake Management

    Fisheries managers often use pond fertilization to improve the biological productivity of a waterbody, resulting in improved fish growth and abundance. As with any management strategy, geographic location, pond owner goals, and primary use of the water body must be considered prior to implementation. If you are interested in the fertilization process (also referred to as productivity manipulation), it’s necessary to first understand how it works in an aquatic environment. Second, it’s important to understand where it is applicable—or not. Last, you should have a thorough idea of what to expect should you choose to employ this technique in your pond.

    How does fertilization work?

    The food web in a pond starts with primary producers, a.k.a. phytoplankton. Dissolved nutrients in the water promote blooms of microscopic algae, which in turn provide food for larger zooplankton and other invertebrates. These organisms are preyed upon by young gamefish and forage fish alike. Fertilization artificially increases the concentration of naturally-occurring nutrients in the pond, like nitrogen and phosphorus. Together, these nutrients provide the fuel that drives this algae bloom and the resulting biological productivity at all levels of the ecosystem.

    Fertilized ponds are capable of significantly increased productivity when compared to infertile ponds. In most cases, fertilized ponds can support 3-10 times more fish biomass compared to unfertilized ponds. As productivity increases, forage fish species thrive on the abundance of food, resulting in improved gamefish growth rates. This also serves to improve the overall number and quality of fish available to anglers. Another potential benefit of the algae bloom is a reduction in rooted plant growth due to the reduced light penetration. Dense algae blooms can effectively “shade out” other photosynthetic organisms. This Increased productivity is not without consequence; the potential for oxygen depletion and pH fluctuation is greater in fertilized ponds. This risk can be mitigated by complimentary management strategies such as pond aeration and liming. In order to avoid potential issues, diligent water quality monitoring is a key component of any pond fertilization strategy.

    Types of lake or pond fertilizer

    There are two categories of lake or pond fertilizer that are typically used in waterbodies: organic and inorganic. Organic fertilizers are plant- or animal-based and include things like manures and plant materials. These fertilizers typically require some decomposition to release their nutrients, so it is important to apply them in well oxygenated areas to help promote proper nutrient release. Organic pond fertilizers are bulky and contain fewer nutrients per pound when compared to inorganic alternatives. Additionally, animal-based fertilizers such as poultry litter should not be applied to ponds used for recreation, due to the potential presence of bacteria that are harmful to humans.

    Inorganic fertilizers are commercially manufactured and don’t require decomposition, so nutrients are immediately available upon application. Nutrient ratios are much simpler to fine-tune due to the known concentration in these products. Inorganic pond fertilizers come in many different varieties and nutrient grades and can be purchased as a liquid, granule, powder or time-release formulation. Your fisheries management professional can recommend a formulation and application program that best fits your fishery goals.

    Big Fish

    When should I fertilize my pond?

    Productivity manipulation is a complex technique, and appropriate application rate, timing, and frequency can vary greatly by region. There are, however, a few guidelines that are widely accepted by fisheries managers when it comes to fertilizing your pond

    • Fertilizer is best applied in the spring or early summer once water temperatures reach 60°F. Algae growth is significantly diminished below this threshold, and fertilization will not be effective.
    • Fertilization can continue through the summer months as needed to maintain the “bloom” of algae. Secchi depth, or water clarity is often used to assess the bloom and determine if more or less fertilizer is necessary.
    • As water temperature drops below 60°F in the late summer and fall, fertilization is typically discontinued. In northern climes, particularly, fertilization can increase the potential for winter fish kills under the ice and is only recommended if other management techniques are employed to mitigate this risk.
    • Fish stocking and recruitment rates must be aligned with the carrying capacity of the pond, which is determined in large part by productivity. If fertilization is ceased once fish populations have been artificially increased, you run the risk of unbalancing the fish community—potentially resulting in poor health, low numbers and stunted growth.

    Other considerations when it comes to pond fertilizing

    Applying more pond fertilizer does not always equate to more growth as there are many factors that influence pond productivity. As with most aspects of freshwater management, maintaining balance is critical. Maintaining a desirable nitrogen to phosphorous ratio is essential to boost the right kind of productivity. It’s also important to note that not all ponds are good candidates for fertilization. While newly created ponds tend to be nutrient poor and respond well to traditional fertilization, in many established ponds or instances where supplemental fish feed is supplied, a phosphorus-only strategy may be applicable.

    Likewise, fertilizers may just be ineffective in your particular fishery. For instance, in ponds with significant flow, fertilization is not a good idea because nutrients with be flushed from the pond before they can be used (and are likely to cause issues downstream as the nutrient-laden water enters other waterbodies). If a pond has an existing nuisance plant or filamentous algae problem, fertilization will exacerbate these issues. Fertilization of ponds containing muddy water should also be avoided as the turbid water shades out productivity, rendering fertilization ineffective. It is also important to consider hydrology—which includes the water source for the pond (surface runoff, groundwater, wetland etc.), water retention time, and destination of outflow—before commencing any productivity manipulation.

    Although there are many things to consider before fertilizing your pond, when appropriately applied by an experienced fisheries management professional, this technique can significantly improve fish growth and abundance. If you want to improve angling opportunity and enhance your fishery, fertilization may help you reach that goal. Remember, proper planning, professional implementation, and continued monitoring are central elements of successful management and will help ensure your lake or pond continues to meet your goals for years to come.

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    ben-german-webBen German is a Fisheries Biologist based out of SOLitude’s Shrewsbury, MA office. He specializes in fisheries management, water quality monitoring and analysis, aquatic plant identification and the study of invertebrate communities. Ben earned a Bachelor’s degree in Fisheries and Aquaculture from SUNY Cobleskill, as well as a Master of Science degree in Lake Management from SUNY Oneonta.

    SOLitude Lake Management is a nationwide environmental firm committed to providing sustainable solutions that improve water quality, enhance beauty, preserve natural resources and reduce our environmental footprint. SOLitude’s team of aquatic resource management professionals specializes in the development and execution of customized lake, stormwater pond, wetland and fisheries management programs that include water quality testing and restoration, nutrient remediation, algae and aquatic weed control, installation and maintenance of fountains and aeration systems, bathymetry, shoreline erosion restoration, mechanical harvesting and hydro-raking, lake vegetation studies, biological assessments, habitat evaluations, and invasive species management. Services and educational resources are available to clients nationwide, including homeowners associations, multi-family and apartment communities, golf courses, commercial developments, ranches, private landowners, reservoirs, recreational and public lakes, municipalities, drinking water authorities, parks, and state and federal agencies. SOLitude Lake Management is a proud member of the Rentokil Steritech family of companies in North America.

    Topics: Fisheries Management, Fisheries Projects