The sluiceways at Units 1 and 3 should substantially reduce the impact of impingement on juvenile 

 and adult winter flounder. This is particularly important as apparently a relatively large proportion of 

 impinged adults did not spawn before encountering the intakes. Studies at NUEL are currently underway 

 to examine the effectiveness of the Unit 3 sluiceway in returning winter flounder and other species to 

 Niantic Bay. 



Entraiiunent 



Abundance 



Sampling at the discharges of MNPS Units 1 and 2 to estimate the number of winter flounder larvae 

 entrained through the condenser cooling water system has been conducted since 1 976. This is the longest 

 time-series of data at NUEL with consistent yearly sampling on the abundance of larval winter flounder. 

 Generally, larvae were entrained from late February through the end of June with greatest densities from 

 mid- April through May. Over 60% of the larvae entrained during the 10-yr period were 5.0 mm and 

 larger (Fig. 31). Since 1983, the proportion of Stage 1 larvae entrained was 2%, Stage 2 was 31%, Stage 

 3 was 56%, and Stage 4 was 11%. As stated previously, smaller larvae are not abundant in the Niantic 

 Bay and therefore are less susceptible to entraiimient. 



Since 1982, the median has been used as a measure of the armual entrainment density and in calculating 

 the total number of winter flounder larvae entrained. A median was used instead of a mean because the 

 data were highly skewed and the median was a better estimate of central tendency (NUSCo 1983a). 

 Selection of the time period used to calculate the median was changed for this report. Previously, the 

 median calculations were based on an annual time period selected by examination of the aimual density 

 distribution over time with an arbitrary determination of the beginning and end of the season. For this 

 report, the season was determined as the period in which 95% of the total cumulative abundance occurred, 

 excluding samples containing the first and last 2.5% of the cumulative abundance over time. This method 

 reduced the number of zero density values used in the calculations. Prior to 1982, entrainment estimates 

 were based on weekly means multiplied by the total weekly volume of water passing through MNPS. 

 These weekly values were then summed for an annual estimate, but confidence intervals could not be 

 calculated. Comparison of the results of these three methods (NUSCo 1983c, 1986a, and this report) 

 indicated large discrepancies among the the estimates. Further evaluations of techniques for estimating 



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