Managing Fish Populations in Ponds

Understanding Fish and their Temperature Needs

Fish management is a continuous and necessary process that helps stabilize fish populations, which is why it’s important to understand that different fishes have specific water temperature tolerances. Warm-water fishes like large-mouth bass and sunfish prefer temperatures above 80°F in the summer, while cold-water fishes like trout can’t survive if the water temperature exceeds 75°F. In between are fishes like small-mouth bass that can adapt to either condition.

Trout are often stocked during springtime or fall, and fished out before the water temperature reaches lethal levels in the summer. In rare cases where cold water continues to rush beneath the pond, trout may survive throughout the entire year. In this case, trout typically do not reproduce and require restocking every three years to maintain fish populations.

Understanding Fish Habitats

Creating the perfect underwater habitat for aquatic animals is best done during the construction phase of a pond. Before filling it with water, one can easily craft rock ledges and undercut banks, pile bushes to create a reef, and submerge large branches that will provide great habitats for fish.

Many other methods exist to improve fish habitats within ponds. The installation of diffuse aerators at the very bottom of the body of water can also increase the vertical habitat by allowing fish to live in levels previously low in oxygen.

Excessive aquatic vegetations are a common complaint among pond owners, but moderate amounts of aquatic plants provide significant habitats for fish. Submerged and rooted vegetation allows young fish and guppies to escape predators, while floating plants like water lilies provide overhead cover and encourage fish to prey on insects.

Understanding Fish Kills

Don’t worry too much about finding one dead fish in your pond. Unless you see a pattern, it’s usually nothing serious since fishes are prone to succumbing to wounds from predators and fishing hooks. Some alarming causes that reduce fish populations include:

1. Oxygen Depletion

If the number of dead fish becomes a growing problem, low oxygen may be the issue at hand. This problem becomes apparent once the fishes begin swimming near the surface, most especially in the morning, and are frequently gasping for air. Problems with low oxygen usually occur during the summertime when aquatic plants dry up or die from the use of aquatic herbicides.

Prevent fish kills due to oxygen depletion by following these management procedures:

  • Avoid treating more than one-third of a pond with an aquatic herbicide.
  • Don’t use aquatic herbicides when water temperatures exceed 80°F since warm water naturally contains less oxygen.
  • Clear piles of snow from small patches of ice to allow sunlight into the pond.

If oxygen depletion persists as a problem, consider installing an aeration unit in the pond. Not only do aerators keep dissolved oxygen from flowing, but it also prevents ice formation on ponds, minimizing the susceptibility of winter kills. Since oxygen depletion is common in shallow ponds, deepening it will lessen its vulnerability.

2. Diseases

Diseases that attack fish are commonly caused by a variety of bacteria, viruses, or parasites living within the body of water. Fish usually fall victim to diseases when experiencing stress from spawning activities or water quality issues. Often, diseases only affect one type of species and rarely cause large-scale fish kills. Unless the body of water continues to decline in quality, the fish population is bound to recover.

3. Water Pollutants

Water pollutants such as runoff from pesticides, fertilizers, and animal feces can increase the death toll of fish since it allows bacteria to thrive, as well as deplete oxygen levels. Many pesticides, especially insecticides used on crops or lawns, are incredibly toxic to fish. Aquatic herbicides that kill overgrown plants and algae also result in killing fish. Make sure to carefully follow the instructions found on product labels to avoid applying too much of the toxic chemical into your pond.

Measuring Fish Populations

Many lake owners have little or no knowledge of the current status of their pond fishery. Hiring a fisheries biologist to test the water with a boat electrofishing unit is an accurate method to determine fish populations. This technique uses a small electrical current to stun the fish, making it easy to capture, identify, measure, and return them to the pond. Using the data from the electrofishing survey, the fisheries biologist can provide a detailed assessment of the pond’s fish population, along with stocking and harvest recommendations to reach the owner’s goals.

Proportional Stock Density or PSD

A more straightforward method that adequately assesses the current status of a pond’s fish population is the use of proportional stock density. The PSD method applies to ponds dominated by a combination of largemouth bass and bluegills.

This method involves the process of keeping records which help pond owners determine the numbers and sizes of fish caught. Significant data includes the length, weight, sex, approximate age, reproductive success, growth, and survival rate of a fish. These records assist in evaluating the status of fish populations. The more data a pond owner collects, the more accurate the total will be. Pond owners can accomplish a useful set of data by maintaining angling records during an entire summer or by inviting many anglers to fish over a span of two weekends. Either approach would result in a significant number of angler hours.

A Final Word

Ponds with growing fish populations provide great sporting and aesthetic entertainment, especially when owners exert effort into taking proper care of them. Problems with unbalanced fish populations are salvageable with the tips presented in this article. Once you identify the source of the problem, performing strategic fish management schemes and having a bit of patience will usually provide satisfactory results.

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