Balancing Fisheries Management and Water Uses for Impounded River Systems

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<em>Abstract</em>.—The Idaho Department of Fish and Game has stocked fingerling Yellowstone cutthroat trout <em>Oncorhynchus clarkii bouvieri</em>, hybrid trout (rainbow trout <em>O. mykiss</em> × Yellowstone cutthroat trout), and brook trout <em>Salvelinus fontinalis </em>(hereafter referred to collectively as trout) in Henrys Lake since the early 1900s to supplement natural recruitment and increase angler catch rates. Annual stocking rates have varied from 317 to 1,027 fingerling (approximately 75 mm) trout per hectare from 1971 to present. Stocking densities can influence angler catch rates but are limited by production constraints and costs associated with raising and transporting fish. By refining fingerling trout stocking densities, managers can optimize the fishery and minimize hatchery expenditures. To fully understand the effects of stocking density on angler catch rates in a lake with natural reproduction, we estimated the contribution of hatchery fish to the fishery by analyzing 6 years of marked fingerling stockings and found that natural recruitment added little to the adult population. We then explored the relationships among stocking densities, angler catch rates, and size of fish harvested by anglers to determine the optimal stocking density needed to achieve our management objectives of catch rates 0.7 fish per hour and 10% of harvested Yellowstone cutthroat trout exceeding 500 mm. We found increased catch rates following years when stocking densities were high. However, mean size of Yellowstone cutthroat trout harvested decreased following years of higher stocking densities. We estimate that approximately 737 fingerling trout per hectare are needed annually to achieve angler catch rates of 0.7 fish per hour. At this stocking density, we estimated that approximately 3% of harvested Yellowstone cutthroat trout would exceed 500 mm. This fell below our management objective of 10% of harvested Yellowstone cutthroat trout exceeding 500 mm and suggested that our current catch rate objective and size objective may be incompatible. This information should be combined with angler opinion data to formulate attainable goals for the fishery.