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Direct impacts may be measured by various means : entrainment 

 effects may be directly measured, modeled from design specifications and 

 species tolerance data, or inferred from monitoring of the base popula- 

 tion. Impingement is most frequently measured by counts and measure- 

 ments of impinged organisms , while thermal effects are usually measured 

 by before/after monitoring of the receiving waters to detect changes in 

 patterns of size, abundance or distribution concomitant with changes in 

 operational status of the plant. In New Haven Harbor, long-term pre- 

 operational and operational monitoring and direct measures of impinge- 

 ment were chosen to assess entrainment, impingement and thermal effects. 

 Study emphasis has been on monitoring patterns of size, abundance and 

 distribution before and after New Haven Harbor Station commenced oper- 

 ation; we believe that the basic concern of environmental protection is 

 non-interference with natural population parameters. As Enright (1974) 

 indicates, measurements of impact such as numbers of various life- 

 history stages killed per year are relevant only insofar as they can be 

 placed in the context of a decision as to whether or not the dynamic 

 equilibrixim of a species or assemblage of species has been significantly 

 altered by the impact. Impacts were assessed on this basis. 



Specifically, patterns of abundance, size and distribution 

 observed before plant operations commenced were compared with patterns 

 found since start-up in July 1975. Differences observed were evaluated 

 in terms of the probability of a causal relationship between plant 

 operations and observed changes. Probability of causality was estimated 

 on the bases of known mechanisms of impact (heat load on the harbor, 

 volvunes of water entrained, numbers of fishes impinged) , established 

 natural variability, and observed influences on the harbor unrelated to 

 plant operations but unique to post start-up monitoring (iinusual weather, 

 dredging, oil spills, etc.). 



In order to evaluate the impacts on finfish populations of 

 other generating station operations (Hess, Sissenwine and Saila, 1975; 

 Saila, 1976; NUSCO, 1977; Stone and Webster Engineering Corporation, 



