Effects of Gizzard Shad Reduction on Relative Abundance, Growth, and Body Condition of Bluegills and Largemouth Bass in a Small Kansas Impoundment

Abstract

AbstractGizzard Shad Dorosoma cepedianum are commonly manipulated as a prey species in the United States but are widely viewed as undesirable in small impoundments because of direct and indirect effects on desirable sport fishes. Montgomery State Fishing Lake in southeastern Kansas became populated with Gizzard Shad during a flood event in 2007, and subsequent monitoring efforts indicated the Bluegill Lepomis macrochirus population was negatively affected. Remedial action involving reservoir dewatering and application of rotenone (target concentration of 7.5 μg/L) was conducted during the winter of 2013–2014, and responses of Bluegills and Largemouth Bass Micropterus salmoides were monitored for 3 years posttreatment. Gizzard Shad were not extirpated following treatment, but their relative abundance decreased 99.8%. Relative abundance of age‐0 Bluegills and Largemouth Bass immediately increased following treatment in 2014 but decreased to pretreatment levels in 2015 and 2016. Conversely, growth of age‐0 Bluegills decreased in 2014, but increased to pretreatment levels in 2015 and 2016. Growth of age‐0 Largemouth Bass slightly decreased following treatment. Growth between the development of the second and third annulus did not differ among years for either species. Body condition of stock‐length Bluegills and stock‐length Largemouth Bass was greatest in 2012 but declined in subsequent years. These results suggest that, contrary to previously published studies, the reduction of Gizzard Shad had minimal effect on Bluegill and Largemouth Bass populations in Montgomery State Fishing Lake. However, intraspecific, density‐dependent functions might have masked true responses of Bluegill and Largemouth Bass growth and body condition to Gizzard Shad reduction. Managers should understand that Gizzard Shad removal or reduction can have variable effects in aquatic systems and should be cognizant of potential outcomes and how those might affect fish populations and associated fisheries.