Characterization of triploid Grass Carp stockings in private waters of Texas
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Grass Carp Ctenopharyngodon idella is used worldwide as a biological control of nuisance aquatic vegetation. Use of triploid Grass Carp in Texas was legalized for stocking on private lands in 1992. Since 1992, landowners seeking to stock triploid Grass Carp must complete a Texas Parks and Wildlife Department (TPWD) permit application, which requires the number of Grass Carp requested, estimated surface area, percent vegetation coverage, and other information on the location and characteristics of the receiving water body. Once applications are received by TPWD, specifics of the application are entered into a database before being approved or denied by TPWD personnel. Purpose of this study was to summarize and characterize the number of permits, number of triploid Grass Carp requested, receiving water body characteristics, and estimated costs in stocking triploid Grass Carp between 1992 and 2020. A total of 30,387 permit applications were submitted, requesting 818,667 triploid Grass Carp of which 793,020 were approved by TPWD. Mean number (± 1 SD) of permit applications per year was 1,048 (± 166), and mean number of triploid Grass Carp requested per year was 28,229 (± 7,881). Trends in permit applications and number of triploid Grass Carp requested were similar between 1992 and 2020. Greater number of requests were for first time, introductory stockings than repeat, supplemental stockings and were from east Texas ecoregions than in central and west Texas ecoregions. Majority of the receiving water bodies were <2.0 ha with >50% submergent vegetative coverage. About 4% of the applications were denied. Estimated cost of stocking ranged between $200 and $400 per ha. Results of this study inform landowners on the practice of triploid Grass Carp as a biological control of nuisance aquatic vegetation but also highlights gaps in information, such as efficacy in controlling aquatic vegetation and the number of triploid Grass Carp stocked, that could benefit TPWD and other natural resource agencies that continue to regulate the stocking of triploid Grass Carp.