Genetics and forage are important
Bass Management 101: growing trophy bass requires fast growth rates and low mortality. Historically, harvest restrictions were used to lower mortality. Now, catch-and-release is practiced by most bass anglers and in many fisheries, mortality is probably as low as it can go. Achieving high growth rates remain an ongoing fishery management challenge. Studies focused on trophy bass offer insights.
It’s well established that Florida bass — fish formerly called “Florida largemouth bass” but now recognized as a separate species — grow larger than largemouth bass, aka northern largemouths, and adding Florida bass genes to a largemouth population increases the catch of trophy bass: fish exceeding 8, 10, or even 12 pounds. Stocking Florida bass creates the possibility of a lake producing fish weighing 10 pounds or better, but biologists have also learned that the first-generation hybrid between Florida bass and largemouth bass also have growth rates similar to Florida bass.
Okay, Florida bass raise the potential for trophy bass catches. But what are the fish — the individual trophy fish — that the anglers are catching?
In Texas, ShareLunker bass weighing more than 13 pounds are genetically tested, and almost all are Florida bass or Florida bass-northern bass hybrids with more than 50% Florida bass genes.
Shortly after Texas started experimenting with Florida bass in the 1980s, Oklahoma introduced Florida bass into their reservoirs. Genetic analyses of tissue samples provided by taxidermists revealed 54% of 251 bass larger than 8 pounds from 34 reservoirs were Florida bass, 28% were first-generation hybrids of Florida bass and largemouth bass, 11% were hybrids with some Florida bass genes, and 11% were pure largemouths.
The Florida bass grew significantly faster. Although growth in weight is not linear throughout the life of a bass, for simple comparison, the average growth rates were 1.3 pounds per year for Florida bass, 1.1 pounds per year for hybrids, and 1.0 pound per year for largemouths.
Similar results have been found in other states within the survival zone of Florida bass, which roughly coincides with states south of a line from North Carolina to Oklahoma, plus eastern Virginia.
Clearly, the presence of Florida bass and their hybrid with largemouth bass raise the chances of catching a trophy bass if the fishery is within the survival zone of Florida bass. But also note that Florida bass genes are not essential for producing largemouth bass weighing 8 pounds or more, as evident from numerous records of double-digit fish from northern states
A study in Florida also used taxidermist-provided data to measure growth rates of 827 Florida bass 10 pounds and larger from 211 lakes throughout Florida. Biologists from the Florida Fish and Wildlife Conservation Commission found growth rates of trophy bass declined from south to north, an expected consequence of the number of days when temperature exceeded 50o F. Growth rate was also positively related to measures of aquatic ecosystem productivity: more nutrients, more forage, faster-growing bass.
The Florida biologists provided an in-depth comparison of two lakes: Lake Pasadena, which had the highest number of trophy Florida bass per acre, and Lake Thonotosassa, which had the fastest growth rate (measured as length) of trophy bass of the lakes studied. Although only observations of single lakes, the comparison suggests several interesting implications.
Growth rates of Florida bass in Lake Pasadena were average. Hydrilla covered a large portion of the lake. The fish assemblage was dominated by centrarchids (fish in the sunfish family), primarily largemouth bass and bluegills. Golden shiners were abundant, but lake chubsuckers had the highest standing crop by weight of non-centrarchid fishes. Shad were scarce. Although bluegill were more abundant than lake chubsuckers, lake chubsuckers were the dominant food consumed by large Florida bass.
Lake Thonotosassa was hypereutrophic (excessive nutrients), lacked aquatic macrophytes, and shad were 72% of the fish biomass. Although bass growth rates were fast, growth in weight slowed beginning at age 6. By contrast, growth in weight of Lake Pasadena bass rapidly accelerated at age 6. Although the abundant shad provided good forage for fast growth to about 18 inches, thick-bodied lake chubsuckers may be a better forage for growing truly large Florida bass.
Good management is directed by good science, and it is not possible to make reliable, scientifically valid conclusions from only two lakes that differ in many ways. The Florida study reverberates that Florida bass grow large, but it also suggests that environmental factors affect growth rates and, thus, trophy bass output.
Of particular interest for future fishery management efforts to produce trophy bass fisheries is the importance of desirable forage for the largest bass in the population. This thought may be as applicable to largemouth bass as Florida bass.
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