CARR and GIESEL: IMPACT OF THERMAL EFFLUENT 



2 

 O 

 9 600- 



10 



5 500 



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to 



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OD 



UTILIZA8LE SPECIES ONLY 



ALL OTHERS 



JUNE JULY SEPTEMBER 



SAN CARLOS CREEK 



SUMMARY 

 HOT SEASON 



HOT SEASON 



NICHOLS CREEK 



Figure 6. — Biomass per 100 m^ of utilizable species in the three creeks as estimated from seine collections. Histograms depicting 



"Summary Hot Season" compiled as described in Figure 3. 



biomass of utilizable species. In Browns Creek, the 

 mullet accounted for only 11 to 37% (average 

 19.2%) of this biomass. The same five species that 

 were cited earlier made the most significant addi- 

 tional contributions to the biomass of utilizable 

 species in Browns Creek. 



DISCUSSION AND SUMMARY 



Elevated water temperature resulting from the 

 discharge of condenser cooling water by the two 

 units of the Northside Generating Station in 

 Jacksonville, Fla. has a detrimental effect on the 

 capacity of two marshland creeks to serve as a 

 nursery area for juvenile fishes during the hot 

 season. Evidence for this detrimental effect is 

 based upon the marked differences in both the 

 density of fishes and the species composition 

 which exist between an ambient temperature 

 creek and two creeks receiving thermal effluent. 

 To the best of our knowledge this is the first field 

 study in which quantitative measurements have 



been reported on the effects of a thermal effluent 

 on the capacity of an estuarine receiving water to 

 continue serving as a nursery area for juvenile 

 specimens, especially those of species having di- 

 rect value to man. Although only the results of the 

 1973 study have been reported here, a prelimi- 

 nary, less-extensive study conducted at the same 

 site in July and September of 1971 revealed the 

 same basic types of differences that are described 

 herein. 



From the standpoint of coastal fisheries opera- 

 tions, the major detrimental effect of the thermal 

 effluent is to decrease the suitability of the habitat 

 for juveniles of species used by man as food and 

 related fishery products. In the thermally affected 

 creeks, both the numbers and the biomass of 

 juveniles of utilizable species were 3- to 10-fold 

 smaller than those encountered in the ambient 

 temperature creek. Regarding these species, our 

 data clearly show that whereas the creek receiv- 

 ing the largest input of thermal effluent affords a 

 nursery habitat dominated almost entirely by 



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