with recruitment indices. The addition of a temperature parameter to the model resulted in a much 

 improved fit to the observed data (R = 0.78). Although the actual mechanisms affecting winter flounder 

 recruitment were unknown, the February water temperature appeared to have been related to and ser\'ed 

 as a good measure of those factors. 



Larval winter flounder studies have been conducted in Niantic River and Bay since 1983 and entrainment 

 data are available from 1976 through the present. During 1986 and 1987, abundance peaked first in the 

 river and then in the bay, which was similar to previous findings; the lag in dates corresponded to flushing 

 rates in the river. Most larvae entering the bay from the river were in Stage 2 of development. 



Greater mortality of larvae occurred in 1987 than 1986, largely early in the season when most larvae were 

 in the river. The effect of jellyfish predation was not as apparent during the past 2 years as it was during 

 1983-85. Examination of length-frequency distributions indicated that most mortality occurred during the 

 3 to 4-mm size-class, suggesting that this was a critical period for mortality. Annual total larval mortality 

 rates, based on the difference in abundance between the 3- and 7-mm size-classes, ranged from 84.6 to 96.9%. 



Most larvae entrained were in Stage 3 of development. As expected, total entrainment estimates for 1987 

 following the start-up of MNPS Unit 3 were among the highest during the last 12 years, even though the 

 median density (number per 500 m ) was among the lowest. Entrainment estimates were dependent upon 

 plant operating conditions as well as larval densities each year. Dates of peak abundance for entrainment 

 samples were positively correlated with March and April water temperatures. From the 12 years of 

 entrainment data, the shape of the abundance curve, as measured by the K parameter of the Gompertz 

 function, was found to be a good predictor of subsequent recruitment of age 3 winter flounder. The shape 

 of the abundance curve was related to February water temperatures, with a narrow, high-peaked curve 

 found during warmer years (low recruitment) and a broad, flatter curve during colder years (high recruitment). 



Laboratory studies showed that larval growth rates were dependent upon water temperature. Of the four 

 temperature regimes examined, optimum temperatures for growth were intermediate (6.9 and 7.5°C), with 

 decreased growth occurring at lower (5.4°C) or higher (10.8°) temperatures. Annual growth rates estimated 

 for 1983-87 using field data collected at Station C in the Niantic River and for 1976-87 using entrainment 

 data were consistent with the findings based on the laboratory data. Again, growth was found to be 

 dependent upon water temperatures. 



Post-larval young-of-the-year winter flounder have been collected at two stations in the Niantic River since 

 1983. Densities at Station LR were higher in 1987 than in previous years. Smaller differences were found 

 in growth of young at both stations in 1986 and 1987 than during 1984 and 1985. Differences among 

 years may have been due to density-dependent growth, especially at LR. Survival rates were very similar 

 among years, regardless of densities of young. 



The winter flounder was the second-most abundant fish impinged on the traveling screens at MNPS since 

 1976. However, relatively few specimens were taken at Unit 2 during the past 3 years because of declining 

 abundance, varying plant operations, and possible reductions related to the construction and operation of 

 Unit 3. The installation of fish return sluiceways at Units 1 and 3 has lessened the impact of impingement 

 on the winter flounder because it has good ( > 85%) survival when returned to the water. Routine 

 impingement monitoring at Unit 2 was discontinued in December 1987 upon agreement between NU and 

 CT DEP. 



viii Monitoring Studies, 1986-1987 



