Sportfish Population Characteristics Following Mechanical Largemouth Bass Removal in Two Small Public Fishing Impoundments in South Carolina

Declining angler harvest rates of largemouth bass (Micropterus salmoides) have increasingly led to small impoundments containing over-crowded largemouth bass populations. Various methods to correct or prevent crowded largemouth bass populations have been used by fisheries man- agers, with mixed results. We removed largemouth bass from two small impoundments in South Carolina using boat electrofishing over two consecu- tive years, with targets of removing 40–50% of the largemouth bass populations each year. We used relative weight (Wr) as the removal criterion, such that all largemouth bass displaying condition Wr < 95 were removed. Largemouth bass population sizes were estimated using mark-recapture in each impoundment for large (≥200 mm TL) and small (<200 mm TL) largemouth bass length groups. A total of 1641 largemouth bass (162.5 fish ha–1) were removed from Jonesville Reservoir (10.1 ha) and 1022 largemouth bass (63.1 fish ha–1) were removed from Lake Oliphant (16.2 ha) in 2020 and 2021. Proportions removed approached the 40–50% removal targets for both length groups at both impoundments in 2020 but fell short of removal targets in 2021 at Jonesville Reservoir. Improved bluegill (Lepomis macrochirus) catch rates and reduced largemouth bass catch rates at Lake Oliphant removals in 2020 led to reduced removal efforts in 2021. Catch rates, estimated population sizes, and estimated biomass (kg ha–1) of large largemouth bass declined from 2020 to 2022 at both impoundments, but results for small largemouth bass were variable. Largemouth bass condition increased at both impound- ments and size structure increased at Lake Oliphant. Bluegill catch rates increased at Lake Oliphant but remained low at Jonesville Reservoir. Bluegill condition and size structure declined at both impoundments from 2020 to 2022. We speculate that the presence of an established threadfin shad (Doro- soma petenense) population contributed to more successful efforts at rebalancing the fishery at Lake Oliphant than at Jonesville Reservoir, which does not have a threadfin shad population. To achieve management goals, removal efforts likely would need to be repeated at both impoundments at regular intervals in the future, raising the question of whether these populations should be renovated and restocked using modified stocking rates or other innovative options to meet management goals more efficiently.

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