Fish Bulletin 148. Effects of Artificial Destratification on Distribution of Bottom Organisms in El Capitan Reservoir

The bottom fauna of El Capitan Reservoir, San Diego County, California, was sampled during 1964, under normal conditions, which included prolonged stratification. The lake was then destratified artificially for 2 years. The benthic organisms, including midge larvae and pupae, oligochaete worms, nematode worms, and freshwater clams, rapidly invaded the profundal zone. They had previously been absent there in summer. Their total numbers in the lake increased dramatically. A combination of anoxia and toxic conditions in the hypolimnion had presumably excluded them from the deeper parts of the lake when it was stratified.In 1967 the lake was permitted to stratify again. By August the normal summer distributional pattern of bottom organisms was beginning to reappear.Extending the distribution of midges throughout the lake by artificial destratification should increase the amount of food available to game fish. This is not so with oligochaetes, clams, and nematodes, which do not usually enter the food chains culminating in game fish. The long-term implications of artificial destratification for reservoir fishery management are discussed