Larval mortality estimates 

 It became evident that survival coefficients for larvae would be 

 necessary in impact assessment modelling to determine if winter flounder 

 larval production in the Niantic River was sufficient to sustain the 

 local population in light of entrainment losses at Millstone. Catch 

 curves were produced for stations and years where data were sufficient. 

 These station-year pairs included the discharge from 1975 - 1981, station 

 5 in 1975 and from 1979 - 1981, station 2 in 1975 and 1978 - 1981, and 

 station 1 in 1974, 1975, and 1981. 



Exponential regressions of the density by 0.5-mm length increments 

 were used to determine length-specif ic apparent mortality coefficients 

 (Table 27). The discharge and station 5 did not have adequate length- 

 density distributions for the calculation of mortality because of the 

 reduced number of smaller larvae in comparison with large larvae. The 

 catch curves produced were flattened or showed an increase in density of 

 larger larvae rather than the expected decrease from mortality. 



Only stations, 1 and 2 had length-density distributions over the 

 full 2 to 9-mm larval size range necessary to calculate mortality using 

 this approach. However, the number of samples taken and the sampling 

 frequencies and methodologies used in the Niantic River varied greatly 

 (Table 28). Until 1980, the need for increased sampling in the Niantic 

 River was not apparent, thus limiting the utility of the data obtained 

 previously. Little useful data were available from Station 2 in 1974, 

 1976 and 1977 as the catch curves from those years were also flattened. 

 Regressions were calculated for 1978 and 1979, but the small sample size 

 made the results somewhat tentative. 



75 



