Largemouth Bass Population Characteristics in a Densely Vegetated Small Impoundment

Michael J. Porta, Richard A. Snow, Clayton P. Porter


Elmer Thomas Reservoir is a small impoundment in southwest Oklahoma that contains a high abundance of the invasive plant Eurasian Milfoil. Because dense vegetation can negatively affect Largemouth Bass, population characteristics (condition, growth, and mortality) of Elmer Thomas Reservoir Largemouth Bass were described. Dense vegetation can impact Largemouth Bass foraging and may reduce angler success, so diet and presence of angler hooking wounds (index of angler catchability) were evaluated on a subset of Largemouth Bass. Condition (mean relative weight) of Largemouth Bass was below average (Wr = 88), which may explain the size distribution skewed towards smaller fish (most Largemouth Bass between 275-400 mm TL). Catch-curve analysis indicates that survival of Largemouth Bass is high (77%). Although high survival estimates suggest that angler exploitation (fishing mortality) is low, it appears that angler catchability is still high (35% of Largemouth Bass had hooking injuries; 45% when corrected for imperfect hooking wound detection). Largemouth Bass diets consisted mainly of fish (76% by number), more specifically age- 0 Largemouth Bass comprised 28% by number and occurred in 20% of the diets. High incidence of age-0 Largemouth Bass in diets suggests a change in behavior as a result of dense vegetation and may help to explain the poor condition and growth of Largemouth Bass. This study suggests that Largemouth Bass are negatively affected by vegetation abundance at Elmer Thomas Reservoir. A vegetation management plan to reduce the vegetation to intermediate bundance levels (~30%) would likely benefit the Elmer Thomas Reservoir fish community and increase shoreline fishing opportunities for anglers.

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