CARR and GIESEL: IMPACT OF THERMAL EFFLUENT 



ALL OTHERS 



-UTrLIZABLE SPECIES ONLY 



ALL OTHERS 



SILVERSIDES 



ALL OTHERS 



ALL OTHERS 



R 



ALL OTHERS 



SILVERSIDES 

 MULLtl 





ilLvlfft 

 PERCH 



MENHADEN 



SSEE3SH 



ThflrAD 

 HERRING 



MENHADEN 



ALL OTHERS 

 SIVER PERCH 



SILVERSIDES 



SPOT 



MULLgf 



irrrgOHarnnQ 



JUNE JULY SEPTEMBER SUMMARY 



HOT SEASON 



SAN CARLOS CREEK 



JUNE JULY SEPTEMBER SUMMARY 



HOT SEASON 



NICHOLS CREEK 



JUNE JULY SEPTEMBER SUMMARY 



HOT SEASON 



Figure 4. — Densities of utilizable species in the three creeks as estimated from seine collections. Histograms depicting "Summary 



Hot Season" compiled as described in Figure 3. 



in Browns Creek. The injection of hot water that 

 was forced through Nichols Creek twice each day 

 (see Figure 2) obviously decreased the value of this 

 second creek as a nursery area for utilizable 

 species. 



Figure 3 also illustrates the change in overall 

 population structure that has occurred in response 

 to the thermal effluent. Whereas in Browns Creek 

 61 to 79% (average 73.2%) of the total fishes in the 

 monthly collections were utilizable species, in San 

 Carlos Creek only 4 to 39% (average 19.4%) of the 

 total specimens could be so categorized. Hence in 

 contrast to the situation in the ambient tempera- 

 ture creek, the majority of the fishes occupying 

 San Carlos Creek during the hot season are 

 species not utilized by man. Dominant among this 

 latter group of temperature tolerant fishes were 

 two species of cyprinodonts {Fundulus grandis 

 and F. heteroclitus) and the gerreid Eucinosto- 

 mous argenteus. Whereas these three species 

 alone accounted for 72% of the total fishes col- 

 lected in San Carlos Creek, these same species 



accounted for only 16% of the total fishes collected 

 in Browns Creek. In Nichols Creek the portion of 

 the population consisting of utilizable species was 

 generally greater than that in San Carlos Creek 

 yet considerably less than that in Browns Creek. 

 Figure 4 illustrates the relative abundance of 

 the various utilizable species collected in the three 

 creeks. In San Carlos Creek, two species of mullet 

 {Mugil curema and M. cephalus) alone accounted 

 for 76 to 96% of the total utilizable species col- 

 lected. In Browns Creek, mullet accounted for only 

 8 to 16% of the utilizable species. Five other 

 species made major contributions to the array of 

 utilizable species present in Browns Creek. These 

 other species were (in order of decreasing abun- 

 dance): tidewater silverside Menidia beryllina, 

 spot Leiostomus xanthurus, Atlantic menhaden 

 Brevoortia tyrannus, silver perch Bairdiella 

 chrysura, and Atlantic thread herring 

 Opisthonema oglinum. Silver perch Bairdiella 

 chrysura were entirely absent from the San Carlos 

 collections. 



75 



