FISHERY BULLETIN: VOL. 73. NO. 1 



attempted to measure in situ the impact of ther- 

 mal additions upon the capacity of an estuarine 

 habitat to continue functioning as a viable nur- 

 sery area, particularly for species of sport and 

 commercial significance. Nugent (1970) provided 

 one of the most complete studies on the effects of a 

 thermal effluent on the estuarine macrofauna in 

 the vicinity of a power station south of Miami, Fla. 

 Nugent concluded that there were both beneficial 

 and harmful effects attributable to the thermal 

 additions but that the overall impact was "detri- 

 mental to many of the economically valuable ani- 

 mals of the waterway." Nugent found that during 

 the hot summer months the heated effluent de- 

 creased the number of fishes present in the dis- 

 charge area and also contributed to the death of 

 certain organisms. However, the methods used in 

 this study for the collection of fishes (gill nets, 

 traps, and hoop nets) are unsuitable for the collec- 

 tion of many juvenile specimens and are some- 

 what inappropriate for estimates of density and 

 standing crop. Grimes (1971) and Grimes and 

 Mountain (1971) studied the effects of a thermal 

 effluent upon marine fishes in the vicinity of a 

 power station near Crystal River, Fla. Their major 

 conclusions were that the natural seasonal abun- 

 dance and the diversity of fishes were slightly 

 altered by fishes being attracted into the heated 

 area during late fall and early winter and by being 

 repulsed during the summer. However the collect- 

 ing methods and the station locations used in this 

 study make the data difficult to assess in terms of 

 the impact of the thermal effluent on the nursery 

 area capacity of the affected area. 



The current study was designed to evaluate in 

 quantitative terms the impact that the discharge 

 of a thermal effluent by a steam electric station 

 had upon the capacity of an estuarine habitat to 

 continue functioning as a nursery area during the 

 hot season. This study was conducted in a marsh- 

 land area to the northeast of Jacksonville, Fla. 

 The data were obtained by analyzing the contents 

 of seine samples taken from shallow-water sta- 

 tions located in three marshland creeks situated 

 in the vicinity of the power station. 



METHODS 



Description of Study Area 



San Carlos Creek, a small marshland creek 

 draining into the St. Johns River, receives the 

 discharge of thermal effluent from the Northside 



Generating Station (NGS) operated for the city of 

 Jacksonville by the Jacksonville Electric Author- 

 ity (see Figure 1). The NGS is situated in a rela- 

 tively undeveloped marshland area to the north- 

 east of Jacksonville approximately 10 miles west 

 of the juncture of the St. Johns River with the 

 Atlantic Ocean. Currently the NGS has two, of an 

 anticipated three, oil-fired steam-electric units on 

 line. Units 1 and 2 of the NGS (550-MW generat- 

 ing capacity) discharge approximately 280,000 

 gallons/min of thermal effluent directly into San 

 Carlos Creek via outfalls situated 150 ft apart. 

 The completion of Unit 3 (550 MW) in 1976 will 

 result in the discharge of an additional 280,000 

 gallons/min of thermal effluent into this same 

 creek. Cooling water for the NGS enters via a 

 flume from the St. Johns River and the heated 

 effluent is discharged into San Carlos Creek at a 

 point approximately 0.75 mile upstream from the 

 river. 



San Carlos Creek and two other physically simi- 

 lar creeks located adjacent to the site described 

 above were used for the collection of fishes de- 

 scribed in the current study. San Carlos Creek not 

 only receives directly the thermal effluent from 



Figure 1. — Study area showing location of Northside Generat- 

 ing Station and marshland creeks adjacent to St. Johns River 

 north of Jacksonville, Fla (see inset). Locations of sampling 

 stations in San Carlos Creek, Nichols Creek, and Browns Creek 

 are indicated by numbers. Juncture of river and ocean is situated 

 about 10 miles to the east. 



68 



