Eutrophication Effects on Prey Size and Food Available to Yellow Perch in Lake Erie

Before 1970, yellow perch Perca flavescens grew at similar rates in Lake Erie's western and central basins. At that time, high rates of nutrient loading were causing rapid eutrophication in both areas so that by the mid-1970s the central basin had become mildly eutrophic while the shallow western basin had reached hypereutrophy. From 1970 to 1983, growth rates of yellow perch in the western basin declined sharply while growth rates increased moderately in the central basin. Modeling of bioenergetics suggests that present differences in yellow perch growth rates are due to interbasin differences in food supply and not to temperature. Direct estimation of yellow perch feeding rates in each basin in 1983 supports this inference. Food limitation in the western basin appears related to a reduced size structure of benthic prey associated with advanced eutrophy. In the central basin, larger benthic prey are available and food consumption rates by yellow perch are high. Food limitation is more serious for larger than for smaller yellow perch in the western basin, and this has apparently caused stunting and population degradation. Further evidence from the literature suggests that changes in prey size structure which accompany eutrophication may be a primary cause of the succession of fish species that occurs as lakes age. Mechanistic understanding of this succession will enhance present capacity to predict fish community responses both to ongoing eutrophication and to the more recent oligotrophication of lakes.Funding for this project was provided by Federal Aid in Fish Restoration, Project F-35-R, Study 6, and Commercial Fisheries Research and Development, Project 3-379-R, Study 1, by contract from the Ohio Department of Natural Resources to the Ohio Cooperative Fish and Wildlife Research Unit

The abundance and distribution of fishes in the cooling-water canal system of an electric generating station : with emphasis on the effect of cooling towers

Vita.Trawl collections were taken from June 1974 to September 1975 to determine the abundance and distribution of fishes in the canal system of the Houston Lighting & Power P.H. Robinson Generating Station with emphasis on evaluating the effect of cooling towers. Surface and bottom, day and night collections were taken from two stations in the intake canal, two stations in the discharge canal afferent to the cooling towers and one station in the discharge canal efferent towers. A total of 91,770 specimens of 63 taxa were taken in 464 collections. Abundant species included bay anchovy, Anchoa mitchilli; Gulf menhaden, Brevoortia partonus; Atlantic croaker, Micropogan undulates; striped anchovy, Anchoa hepsetus; spot, Luiostomus xanthurus; sand seatrout, Cynoscion arenarius; and sea catfish, Arius felis. These seven species accounted for 98.5% of the total catch. Striped anchovy, bay anchovy, sea catfish, and sand seatrout had peak abundance in the intake canal during summer, but were generally absent from the discharge canal. Gulf menhaden, spot and Atlantic croaker were most numerous during winter and were often present in abundance in the discharge canal at this time. There was evidence from length frequency data that spot and Atlantic croaker had established resident populations in the discharge during winter. In general, most fish captured in the discharge canal were recruited from the intake canal via impingement on the plant's revolving intake screens and subsequent sluicing to the discharge. The number of organisms captured in the discharge canal was also dependent on their survival and retention time. During the summer, catches from the discharge canal were generally quite small both afferent and efferent to the cooling towers, and differed little from catches made prior to the construction of the cooling towers. Therefore, it appears that the cooling towers have been generally ineffective in promoting the survival of fishes