Hudson River Fishes and their Environment

Abstract

<em>Abstract.</em>—Pelagic fish abundance and distribution was estimated acoustically at Bowline and Indian Point power plants on the Hudson River, New York, during July, August, and September 1996, in a study designed to determine size-specific spatial and temporal fish abundance and distribution with respect to environmental variables (i.e., photoperiod, depth strata, field). August yielded the greatest (<EM>P </EM>< 0.05) mean density of fish at both power plants. Fish were concentrated in Bowline’s near-field (lagoon) region, thus increasing the potential for deleterious impingement and entrainment effects there. For all size classes, mean fish density was greatest during darkness at both power plants. Generally, the two power plants exhibited similar trends in mean fish abundance with respect to water depth and photoperiod. During July and August mean fish density was significantly higher between 1.5 and 4.5 m (depth strata one) of depth at both power plants. Bowline’s mean fish density was greater under near-field, shallow depth (depth strata one) darkness during July and August. Bowline’s isolated and bathymetrically complex near-field lagoon concentrated pelagic fish compared to the river proper. Hydroacoustics were useful in providing a detailed map of fish distribution relative to each power plant over the course of a few days each month. Hydroacoustic monitoring could mitigate negative effects to pelagic fish at existing and proposed power plants, through sighting of power plant water intake structures or by providing a biological basis for modified production cycles.