Predation of stocked Rainbow Trout in an Alabama tailwater

Abstract

ObjectiveColdwater releases from reservoirs support economically valuable sport fisheries for salmonids in the southern United States. The tailwater of Lewis Smith Dam in northwestern Alabama supports the only coldwater fishery in the state, with monthly stockings of about 1500 catchable‐size (200–406 mm total length) Rainbow Trout Oncorhynchus mykiss. Historically, the return to angler creel has been low in this fishery, and few large Rainbow Trout are caught. Numerous potential predators of stocked trout exist in this tailwater, including Gulf‐strain Striped Bass Morone saxatilis, which are stocked annually in a downstream reservoir. Thus, the objective of this study was to quantify the amount of predation, which occurs on Rainbow Trout in the Smith Lake tailwater.MethodsPotential predators of Rainbow Trout were collected six times over a 3‐week period after stocking in March, May, June, and October 2018.ResultRainbow Trout were found in the stomachs of Striped Bass, hybrid striped bass (White Bass Morone chrysops × Striped Bass), Largemouth Bass Micropterus nigricans, and Chain Pickerel Esox niger. Only Striped Bass exhibited substantial predation on stocked Rainbow Trout, with 75% of these fish having at least one trout in their stomach. Of all identifiable prey items, Rainbow Trout composed 82% of the Striped Bass diet by number across all four sample months and constituted more than 65% of the Striped Bass diet by number in each sample month. Bioenergetics models predicted that a population of 500 Striped Bass living continuously in the tailwater from March through October could consume all Rainbow Trout stocked during each month. If Striped Bass vacated the area or switched from trout to other diet items for one‐third of each month, they could still consume almost 60% of stocked trout.ConclusionResults of this study demonstrate that Striped Bass are significant predators of Rainbow Trout in the Smith Lake tailwater and are likely one of the main factors mediating Rainbow Trout survival and persistence in this fishery.