CARR and GIESEL: IMPACT OF THERMAL EFFLUENT 



Table 5. — Collections of fishes from three stations on Browns Creek during the hot season of 1973. Area seined in June was 685 m*, in 

 July was 676 m^, and in September was 285 m^. Total area seined was 1,646 m^. 



'Station 1 not sampled in September due to mechanical problems. 



Sphoeroides nephelus, were collected only in 

 Browns Creek and not in either of the thermally 

 affected creeks. However, none of the species listed 

 above made a major contribution to the total den- 

 sity of fishes in this ambient temperature creek. 

 Among the other species entirely absent from San 

 Carlos collections, only two species, Anchoa 

 mitchilli and Bairdiella chrysura, made a 

 significant contribution to the fish density in 

 Browns Creek. When considered alone, the differ- 

 ences cited above might be construed to suggest 

 that the nursery capacity of thermally affected 

 San Carlos Creek is not markedly different from 

 that of Browns Creek which functions at ambient 

 temperature. However, a critical comparison of 

 the densities, the biomasses, and the population 

 structure of the fishes in the three creeks reveal 

 some important differences that are described 

 below. 



Figure 3 illustrates the relative densities of 

 both total fishes and utilizable fishes as they ap- 



peared in the monthly samples. The figure shows 

 that the following three major differences existed 

 between the populations present in the thermally 

 affected creeks (San Carlos and Nichols) and the 

 population present in the ambient temperature 

 creek (Browns): 



1. In June and July the density of total fishes 

 was highest in the ambient temperature 

 creek. 



2. Throughout the entire study period the den- 

 sity of utilizable species was markedly 

 higher in the ambient temperature creek. 



3. In the ambient temperature creek, the ma- 

 jority of the population consisted of juveniles 

 of utilizable species, whereas in the ther- 

 mally affected creeks the majority consisted 

 of species not utilized by man. 



In June and July the estimated density of total 



73 



