mined by averaging the four volume estimates 

 from the flowmeters. 



All sampling at EN was conducted with 333-[im 

 mesh nets. On the bongo sampler, 202-[im mesh 

 nets were used from February through the first 

 week of April and 333-|im mesh nets were used 

 during the remainder of the season. The bongo 

 sampler was towed for 6 min at station A, B, and 

 C (filtering about 120 m ) and for 15 min at 

 station NB (filtering about 300 m ). Generally, 

 the net was deployed at EN for 5 to 6 min (fil- 

 tering about 400 m ), but this varied depending 

 upon plant operations (number of circulating 

 pumps). All ichthyoplankton samples were pre- 

 served with 10% formalin. At the three river 

 stations, jellyfish medusae were sieved (1-cm 

 mesh) from the sample and measured volumetri- 

 cally (ml). 



During the occurrence of larval winter flounder 

 in 1986 and 1987, sampling time and frequency 

 varied with station, season and year. At EN, 

 collections were taken during the day and night 

 (two replicates during each) once a week in Feb- 

 ruary and June and similarly during 4 days each 

 week from March through May. Single bongo 

 tows were made at NB biweekly (day and night) 

 in February and March, and weekly in April 

 through the end of the larval winter flounder sea- 

 son, except that weekly day and night samples 

 were collected in March 1987. Preliminary tows 

 were made during the daytime in February in the 

 upper portion of the Niantic River (ice permitting) 

 to determine when larval winter flounder were 

 present. From the first larval occurrence through 

 the first week of April, single daytime tows at 

 each station were made twice weekly within an 

 hour of low slack tide. During the last 3 weeks 

 of April, single day and nighttime bongo tows 

 were made twice weekly. The day samples were 

 collected within an hour of low slack tide and the 

 niglit samples during the second half of a flood 

 tide. During the remainder of the seison until 

 the disappearance of larvae at each station, tows 

 were made twice a week only at night during the 

 second half of a flood tide. This varying sampling 

 scheme, based on information from previous sam- 



pling, was designed to increase efficiency in data 

 gathering and reduce sampling biases (NUSCO 

 1987). 



Only one of the replicates from a bongo tow 

 or entrainment collection was processed in the 

 laboratory. Samples were split to at least one-half 

 volume and larvae were identified and counted 

 using a dissecting microscope. Up to 50 randomly 

 selected winter flounder larvae were measured to 

 the nearest 0. 1 mm in standard length (snout tip 

 to notochord tip). The developmental stage of 

 each measured larva was recorded using the fol- 

 lowing identification criteria: 



Stage 1 . The yolk-sac was present or the 



eyes were not pigmented (yolk- 

 sac larvae) 



Stage 2. The eyes were pigmented, no 



yolk-sac was present, and no 

 fin ray development 



Stage 3. Fin rays were present, but the 



left eye had not migrated to the 

 mid-line 



Stage 4. The left eye had reached the 



mid-line, but juvenile character- 

 istics were not present 



Stage 5. Transformation to juvenile was 



complete and intense pigmen- 

 tation was present near the 

 caudal fm base 



Larval data analyses were based on standardized 

 densities per 500 m of water sampled. An av- 

 erage of weekly densities was used in analyses 

 because weekly sampling frequencies varied due 

 to sampling design and weather conditions. The 

 geometric mean was chosen because these data 

 generally followed a lognormal distribution (see 

 the Delta Distribution section of this report). 

 Previously, weekly means were determined arith- 

 metically and the results reported in NUSCO 

 (1987) may differ from those herein. For com- 

 parisons of river and bay data and also for some 



Winter Flounder Studies 



155 



