found in 1986. However, in recent years juveniles have been found in more areas throughout the river 

 and in Niantic Bay during the time of the surveys. This variation in distribution makes the estimation 

 of juvenile abundance less certain than that of adults. 



About two -thirds of the total number of winter flounder impinged on the traveling screens of 

 MNPS were taken in winter. Before 1984, annual estimates usually ranged from 4 to 10 thousand with 

 winter storms accounting for large proportions of most annual totals. Sex ratios and reproductive 

 condition of impinged fish differed from fish taken in the river. The predominance of males and of 

 gravid females in the collections indicated that at times impingement was related to behavior of winter 

 flounder. A fish return sluiceway was installed at MNPS Unit 1 in December of 1983 and studies 

 showed that survival of returned winter flounder would be considerable (ca. 80-90%). This greatly 

 reduces the impact of impingement on the winter flounder. 



Entrainment sampling has been conducted since 1976. A majority (>60%) of the winter flounder 

 larvae entrained were 5 mm and larger. The greatest entrainment densities occurred from mid-April 

 through May. Based on the median aimual entraiimient density, three years were low (1977-79), four 

 years were high (1976, 1980-83), and the remaining years were intermediate. Annual entrainment was 

 related to total egg production in the Niantic River and the length of time a larva was susceptible to 

 entrainment was related to water temperature. The effects of entrainment on larval winter flounder were 

 examined in the laboratory and field. Larvae 5 mm and larger were able to survive a AT of 13 °C for 

 up to 9 h. The estimated critical thermal maximum was approximately 24 °C. A mortality study 

 showed that about 80% of the Stage 4 larvae would have survived entrainment. 



Impact assessment was addressed using a deterministic model developed by the University of Rhode 

 Island. The model, subdivided into hydrodynamic, concentration, and population submodels, predicted 

 a 5 to 6% decrease in the Niantic River population after 35 yr of MNPS operation. Based on the 

 initial assumptions, the model results were probably conservative. A new stochastic population dynamics 

 model, which takes into account the natural variability in the recruitment process, is currently under 

 development at NUEL and will provide a more realistic estimate of potential losses. 



To date, there is no evidence that MNPS has significantly affected the local winter flounder 

 population. Variability in annual abundance appears to be related to natural events and has been noted 



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