Spatial Distribution of Entrained Fish Larvae in a Power Plant Discharge Canal

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Abstract
Larval fish were sampled with plankton nets during June and July at 1-, 3-, and 5-m depths at three stations in the 6-m-deep discharge canal of the Monroe electricity-generating plant on western Lake Erie. Of nine species, gizzard shad (Dorosoma cepedianum) accounted for 96% of all larval fish collected in June and, along with freshwater drum (Aplodinotus grunniens), 78% of those taken in July. Densities of fish larvae at the three depths, and at two of the three stations sampled, were not significantly different. Mean densities of gizzard shad and total fish larvae in June were significantly higher at one station. Fluctuating and significantly lower velocity at that station, causing the flowmeter not to turn while the net was still filtering water, was suspected of causing inflated densities. Generally sizes of larvae were not stratified by depth or station; differences that were found were small. Thus, we concluded that to obtain samples with representative species, densities, and sizes of entrained fish larvae, a stationary net should be positioned where the water has uniform high velocity and is well mixed.

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