Distribution and Condition of Fishes in a Small Reservoir Receiving Heated Waters

Abstract

The effects of a thermal effluent on the distribution and condition of fishes were determined in a 330-ha reservoir in northeastern Texas. Fish were collected at five stations with 41-m experimental gill nets and a 6.1-m seine every 2 weeks between May 1971 and June 1972. Water temperatures at the mouth of the effluent canal were highest (42.2 C) in July and were typically 3-8 C higher at this location than in other areas of the reservoir. Two forage species (Mississippi silversides, Menidia audens, and pugnose minnow, Notropis emilae) were never found near the mouth of the effluent canal. White crappie (Pomoxis annularis) and river carpsucker (Cyprinus carpio) may have been attracted to the effluent area in spring and summer. Channel catfish, (Ictalurus punctatus), gizzard shad (Dorosoma cepedianum), threadfin shad (D. petenense), and bluegill (Lepomis macrochirus) were rather evenly distributed over the entire reservoir during all seasons. The size and condition of fishes collected at the mouth of the effluent canal were not significantly different from those of fish collected at other stations in the reservoir, although the condition coefficients of channel catfish, river carpsucker, gizzard shad, threadfin shad, and bluegill were lower than those reported for these species in other parts of the United States. The results suggest that in a small reservoir like North Lake the effects of a heated effluent on fish populations may be generalized over the entire body of water, particularly when a cool-water refuge area is present beneath the heated surface stratum.