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Title:	Effects of reservoir water levels on year-class development and the abundance of harvestable fish
Authors:	Aquatic Ecosystem Analysts. Environmental and Water Quality Operational Studies (U.S.) Ploskey, Gene R. Aggus, Larry R. Nestler, John M.
Keywords:	Fisheries Fishes Fish Ecology Hydrology Reservoir ecology Reservoirs Water levels
Publisher:	Environmental Laboratory (U.S.) Engineer Research and Development Center (U.S.)
Description:	Technical Report Abstract: This report supplements findings of Technical Report E-84-8, which documented quantitative relations between seasonal and annual water levels and the reproductive success of fishes in reservoirs. In this study, the development of year classes of fish was examined in detail to clarify the effects of fish reproductive success on the future abundance of fishes of a harvestable size. Qualitative results indicated that increased production of young fish consistently increases the abundance of harvestable-size fish within 1 to 4 years, barring catastrophic mortality of young fish before they recruit to a harvestable size. However, the abundance of large fish which results from recruitment of young fish could not be quantified because of variable rates of mortality and growth, as well as a lack of accurate age and growth data. The single most important variable affecting the production of harvestable fish is mortality. Major sources of mortality such as starvation and predation often can be reduced by manipulating water levels during the growing season. Condition (weight at a discrete length) of largemouth bass was positively correlated to average surface area in summer and maximum change in area per year. Mortality due to starvation was apparently reduced by extensive spring flooding and above-average summer water levels. Above-normal water levels in summer also may reduce predatory mortality of young fishes by providing additional refuge from predators. The degree to which a single year class of fish dominates a population apparently is influenced by the extent of annual and multiyear changes in water levels. Fish exhibited boom and bust patterns of recruitment in Bull Shoals Lake, Ark., where water levels changed extensively within and among years. In contrast, annual recruitment of fish was more uniform in John H. Kerr Lake, Va., where water levels varied less extensively within and among years than in Bull Shoals Lake.
Rights:	Approved for public release; distribution is unlimited.
URI:	http://hdl.handle.net/11681/4566
Appears in Collections:	Technical Report