INTRODUCTION 



The Millstone Nuclear Power Station (MNPS) located in Waterford, 

 Connecticut, consists of two operating electric generating plants and a 

 third plant scheduled to begin operation in 1986. The MNPS currently 

 uses 5.3 x 10 m of water per day for cooling purposes and returns this 

 water to Long Island Sound with an increased temperature ( A -t) of 12 C 

 (NUSCo 1982) . During three-unit operation, the volume of cooling water 

 requried by MNPS will increase to 10.2 x 10 m /day but the 

 A-t will drop to 10°C above ambient (NUSCo 1982). Northeast Utilities 

 Service Company (NUSCo) has established an extensive monitoring program 

 at their Environmental Laboratory (NUEL) to assess the impact of construc- 

 tion and operation of the power plants on indigenous fish populations. 



Impacts from MNPS may be expected to arise from several sources. 

 Larger adult fish may be removed from the population by impingement on 

 the intake screens. Larvae and small fish may be removed during entrain- 

 ment through the cooling water system. Those populations experiencing 

 such losses would, then, be subject to increased mortality rates. The 

 effects of increased mortality rates on finfish abundances are varied 

 (Ricker 1975) and the magnitude of the effects depends on the size of 

 the increased mortality as well as on the size and age structure of the 

 affected population and any compensatory mechanisms in the reproductive 

 cycle. Additionally, the geographical distribution of local fish popula- 

 tions may be altered in response to thermally or physically altered 

 habitats. Localized water temperature increases could either attract 

 fish to or exclude fish from areas that did not meet their thermal 

 requirements. Physical alteration by rip rap accumulation or bottom 



