648 CHUNG AND STRAWN 



Since recordings of salinity from the intake and discharge canals 

 were similar, only intake-canal salinity is presented. Salinity ranged 

 from 1 to 24.8 ppt in the intake canal (Fig. 1), and there was a 

 striking difference between the 2 years, with values ranging from 6.8 

 to 24.8 ppt in 1974 and from 1 to 12.4 ppt in 1975. This was 

 especially true in early June and early July; in 1975, salinities were 

 5.3 ppt or less and, in 1974, 10.3 ppt or more. This was caused by 

 heavy rains in early June and early July 1975. 



Multiple regression analyses indicated that intake-canal tempera- 

 ture was the most significant factor influencing thermal tolerance of 

 aquatic animals and that salinity was less significant (Chung, 1977). 



Predicted Survival in Discharge-Canal System 



In the hot season (June— September), mortality rates of crusta- 

 ceans and fishes tested at 35° C (discharge-canal temperature efferent 

 to the cooling towers in the hot season) were for all species except 

 one crustacean, white shrimp (Penaeus setiferus), and 17 fishes 

 (Table 1), and rates were very low for the white shrimp and nine of 

 the fishes (0.0001 to 0.0024/min). 



In the hot season most aquatic animals transported by the power 

 plant from intake water and exposed to the elevated temperatures of 

 the effluent die of thermal shock between the plant and the cooling 

 towers (Table 1). Except for the rough silversides during the hot 

 season, no mortalities were predicted for any species in any season 

 downstream of the cooling towers because all individuals of most 

 species died before reaching the towers and any surviving individuals 

 of resistant species were able to withstand the greatly reduced 

 temperatures between the towers and the ambient water in Galveston 

 Bay. At the average cool-season temperature of the discharge canal, 

 100% of all species except the bay anchovy survived, and, at the 

 average cold-season temperature, all animals tested were predicted to 

 survive. Expected survival probabilities after direct passage through 

 the discharge-canal system (30 min in the discharge canal afferent to 

 the cooling towers and 150 min efferent to the towers) ranged from 

 to 96% for the species studied. All individuals from intake water, 

 except for those of 6 species of crustaceans and 15 fishes (Table 1), 

 would be expected to die during the summer (Jime— September) at 

 the average discharge-canal temperature. The exceptions are grass 

 shrimp, Palaemonetes pugio (48% survival) and P. vulgaris (53%); 

 river shrimp, Macrobrachium ohione (3%); white shrimp, Penaeus 

 setiferus (10%); browii shrimp, Penaeus aztecus (46%); blue crab, 

 Callinectes sapidus (76%); lady fish, Elops saurus (38%); sea catfish, 

 Arius felis (18%); Atlantic toadfish, Opsanus beta (39%); sheepshead 



(Text continues on page 658.) 



