A comparison of occurrence and abundance of fishes within three Texas reservoirs which receive heated discharges

Occurrence and abundance of fishes were studied in heated and non-heated areas of Lake Bastrop, Lake Nasworthy and North Lake reservoirs used for cooling by power plants. On monthly trips fishes were captured at night by seine, trawl and gill net at standard stations. Measurements of temperature, dissolved oxygen content, pH and conductivity were taken. Among reservoirs there was an inverse relationship between maximum megawatt load per surface hectare of reservoir and abundance of fish, but differences in fertility and species composition were thought to explain better than heat most differences among reservoirs. Lake Bastrop was essentially a bass-sunfish pond; Lake Nasworthy was just past its peak years of production and contained large populations of several species; and North Lake maintained low stable fish populations dominated by rough fishes. Large gizzard shad utilized the shallow parts of the reservoirs (discharge areas included) during late winter and early spring to spawn. At Lake Nasworthy this occurred approximately a month earlier in the heated than in the non-heated area. Subadult and adult gizzard shad concentrated in the heated area of Lake Nasworthy during the latter part of each year. Significantly more gizzard shad, 101-209 mm long, were trawled in the heated area of Lake Nasworthy than in the non-heated area. Gizzard shad less than 60 mm long were not taken in the discharge canal. Some threadfin shad were taken in Lake Bastrop and North Lake and there were no significant differences between heated vs. non-heated areas. Carp populations in the reservoirs were small. Peak catches of carp during late winter and spring were related to spawning readiness. Sexually ripe carp migrated up the discharge canals as if they were inflowing streams. ..