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Increasing the Average Size of Largemouth Bass

Posted May. 1, 2010

Largemouth bass is the most popular fish in south-central Oklahoma and north-central Texas private impoundments. In this area, more landowners manage for and more fishermen fish for largemouth bass than any other species in private impoundments. Although fishermen enjoy catching substantial numbers of bass, most fishermen want to catch some large bass.

Each impoundment has a capacity to produce a certain biomass (overall weight or amount) of largemouth bass.

This biomass depends upon impoundment surface area, water quality, fertility, phytoplankton (microscopic algae) production, invertebrate production, prey fish abundance, prey fish size distribution, bass size distribution and other factors. Most unfed and unfertilized impoundments in this area containing both largemouth bass and bluegill have 15-75 pounds of bass per surface acre, but their overall range of bass biomass is approximately 0-174 pounds of bass per surface acre, with relatively few having more than 100 pounds of bass per acre.

Largemouth bass size distribution is typically best in impoundments larger than one-half acre (preferably larger than 1 acre) with good water quality, adequate phytoplankton or visible aquatic vegetation, and appropriate numbers of bass and bluegill. Largemouth bass biomass and size distribution are generally poor in relatively infertile, clear impoundments without aquatic vegetation. To allow improvements in largemouth bass abundance and size distribution in such situations, several grass carp should be removed if present or impoundments should be fertilized.

Impoundment water should have total alkalinity greater than 20 parts per million calcium carbonate equivalent, pH of 6.5-9 at dawn, a greenish color and, generally, an average visibility of 10-30 inches.

However, visibility can be clearer when aquatic plants dominate 10-25 percent of an impoundment. When water quality and plant community (phytoplankton or visible aquatic plants) do not fit these parameters, they should be addressed before expecting improvements in bass size.

Prey fish biomass and size distribution must be adequate to support large bass. A largemouth bass fishery will not have many large fish over the long term without abundant prey fish. Bluegill is the most appropriate prey fish for largemouth bass in impoundments. When prey fish are absent or scarce in an impoundment with suitable water quality and plant community, adequate numbers and sizes of bluegill should be stocked to increase largemouth bass size.

To increase the average size of stunted largemouth bass in an impoundment with suitable water quality, plant community and prey fish, the number of stunted bass must be reduced. When too many largemouth bass are present, they quit growing or grow very slowly because more bass are present than available prey. As an example, if an impoundment supports 45 pounds of bass biomass per acre and 90 adult bass per acre are present, the average bass size will be about one-half pound (about 10 inches long). A crowded, stunted largemouth bass fishery is fairly common in impoundments. Typically, the vast majority of adult largemouth bass are smaller than 13 inches, and few are larger than 20 inches in crowded, stunted bass fisheries.

The number of stunted bass that should be removed from an impoundment to improve size depends upon bass biomass and other factors. Unfortunately, it is difficult to determine biomass. When water quality, plant community and prey fish are appropriate, I suggest initially trying to remove about 10 pounds of stunted bass per acre during a year. If this harvest rate does not improve average size, I suggest increasing stunted bass harvest rate by 5-10 pounds per acre annually until average size improves. Bass larger than the stunted sizes should be returned to an impoundment (catch and release) because 2 pounders are necessary to grow 3 pounders, 3 pounders are necessary to grow 4 pounders, etc. Also, larger bass help reduce the number of smaller bass by consuming them.