Effects of Wintertime Stocking of Rainbow Trout on the Forage Community of an Oklahoma Impoundment

Abstract

AbstractRainbow Trout Oncorhynchus mykiss are sometimes stocked to create put‐and‐take fisheries in small impoundments. Information about the effects of these stockings on existing piscivores is poorly understood. Therefore, we performed a study to evaluate the forage consumption by Rainbow Trout stocked in Lake Carl Etling, Oklahoma. A creel survey during the 2014–2015 trout season determined that angling pressure was low, which left the majority of stocked trout in the lake until their thermal maximum was exceeded in late May–June. Rainbow Trout stomach contents were collected monthly from November through April annually (2015–2018) via gastric lavage. Gizzard Shad Dorosoma cepedianum were consumed during most months, but their occurrence in Rainbow Trout stomachs was highest in January and December. A sharp decline in Gizzard Shad consumption was followed by an increase in detritus consumption each year. Using either Gizzard Shad numbers observed in monthly Rainbow Trout diets or the estimated monthly abundance of Rainbow Trout, we postulated that Rainbow Trout substantially affected age‐0 Gizzard Shad biomass (reducing it by 66.7 or 54.6 kg/ha, respectively), potentially negatively affecting growth rates of other piscivores in the system. This study demonstrates the unintended consequences of stocking an additional predatory fish into small impoundments and the importance of evaluating angler harvest of these stocking programs to ensure the stocked species receives sufficient angler harvest to match stocking rates and prevent negative impacts on the fish community (both forage and other piscivorous species).