11-111 



Nekton 



Strongly swimming organisms such as juvenile and adult finfish 

 can also be impacted by a thermal plume if they remain in it. The 

 effects of excessive heat exposure may reduce the ability of individuals 

 to avoid further stressful situations. Spigarelli (1975) showed that, 

 although populations of certain species of fish tend to concentrate in a 

 thermal plume, the durations of exposure for individuals were brief. Of 

 the 16 representative species there are nine that have been, or might 

 be, attracted to the New Haven Harbor Station thermal plume. These 

 include: alewife, blueback herring, American shad, menhaden, scup, 

 weakfish, bluefish, bay anchovy and striped bass. In the case of New 

 Haven Harbor Station, the heated water used for condenser cooling is 

 discharged from a diffuser pipe extending several hundred feet from 

 shore into water approximately 35 feet deep. At the calculated dis- 

 charge velocity, mixing occurs rapidly resulting in a small surface 

 plume that can be occupied by fish. Due to the actions of wind, waves, 

 and tidal currents, the plume is probably somewhat mobile. To remain in 

 the plume, fish must reposition themselves periodically, thereby 

 unavoidably encountering near ambient conditions. Kinne (1970) and 

 others (Wolf son, 1974; Miller and Beck, 1975) have concluded that the 

 intermittent nature of the heat exposure considerably reduces the 

 chances of developing symptoms such as those indicated in Table 11-6. 

 Considering the small size of the plume, its changing shape and dis- 

 tribution, and the motility of these species, it is unlikely that the 

 small percentage of individuals who might develop symptoms of heat 

 exposure will substantially affect the ability of the species in ques- 

 tion to sustain present population levels. 



- Impaot 



An important consideration in assessing power plant impact is 

 change in species abundance after plant operation begins. Table 11-7 

 summarizes by month the relative abundance of representative species 



