MOVEMENT OF THREE SPECIES OF FISHES 543 



maximum temperature areas horizontally and vertically by moving in 

 the cooler water. 



DISCUSSION 



The seasonal temperature patterns associated with the thermal 

 discharge followed trends typical for the ambient temperature. The 

 diurnal flow fluctuations imposed by discharge from upstream 

 altered temperature distributions, however. During the cooler months 

 heated water was rapidly diluted, and there was little effect, even 

 immediately across the river from the plant. During the summer and 

 early fall, however, when river flow was lowest and ambient river 

 temperature was highest, the heated effluent had a marked effect on 

 the area within several kilometers of the plant. The fluctuating 

 thermal zone occasionally spread completely across the river, 

 creating a potential intermittent surface barrier with a continuous 

 underflow of cooler water. 



During the critical months of late summer, channel catfish no. 2 

 passed the thermal zone by avoiding the high surface temperatures 

 and moving instead in the cooler, deeper water. The flathead catfish 

 moved past the plant at least four times between Aug. 27 and 

 Sept. 11. No observations were recorded as the fish moved directly 

 through the thermal zone, but these passages indicated that the 

 thermal plume did not prevent these two species from moving 

 upriver or downriver past the plant. 



Based on the observed movements of largemouth bass no. 8 in 

 September, we can state that this species seems capable of passing 

 the thermally influenced area during most critical times of the year. 

 The bass passed the thermal zone during the season of maximum 

 temperature development (September) at least four times, each time 

 moving past on the side of the river opposite the plant at a depth of 

 3 to 7 m, apparently in the cooler water. 



Thermal discharge with the flow pattern described did not 

 present an impassable barrier to the fishes studied during the 

 warmest part of the year. Little can be inferred as to the proportion 

 of a population that might pass, but since individuals of three species 

 were not impeded we can conclude that passage was possible for 

 those species. 



ACKNOWLEDGMENT 



The research reported here was supported by the U. S. Fish and 

 Wildlife Service; the Game and Fish Division, Alabama Department 



