and the other near bottom. In 1983, samples were collected at the time of maximum ebb and flood tidal 

 currents during three tidal cycles (two cycles on May 9 and one on May 16). In 1984 and 1985, samples 

 were collected hourly except for 1 h before and after slack tidal currents during five tidal cycles (April 4 

 and May 8 in 1984; March 28, April 29, and May 28 in 1985). The 1984 and 1985 data were combined 

 along with current velocity from the flowmeters to calculate the net exchange of larvae leaving and entering 

 the river. 



Ebb and flood tide velocity measurements used in estimating net larval exchange may not have been 

 comparable due to the different widths of the channel at the point of sampling. Due to the length of the 

 mooring line tied to the bridge, the actual sampling location was approximatedly 10 m north of the bridge 

 during a flood tide and approximately 10 m south of the bridge during an ebb tide. The comparability 

 of velocities was investigated by fitting a second order polynomial equation to the water velocity measure- 

 ments over time during the five flood and ebb tidal phases sampled in 1984 and 1985. Because there is 

 minimal freshwater input into the Niantic River, the area under the fitted curves for flood and ebb tides 

 should be similar in magnitude. If the areas differ, then adjustments to velocity measurements of either 

 tidal stage could be made to make the areas similar and velocities comparable (NUSCo 1986a). 



The effects of mesh size and tow duration on net extrusion of larval winter flounder were examined. 

 Comparisons of mesh size were examined in the laboratory (NUSCo 1986a) and in field studies (NUSCo 

 1985). In the laboratory, meshes of 202, 333, and 505 \im were compared. An apparatus was constructed 

 such that the velocity of water could be regulated as it passed through a chamber covered by the various 

 meshes with a similar cross-net velocity (ca. 20 cm/sec) as encountered in field sampling. Ten laboratory- 

 reared yolk-sac to first-feeding larvae (ca. 3-4 mm) were placed in the chamber. The flow was maintained 

 for 15 min, the chamber was removed, and the number of larvae retained was counted. From 9 to 18 

 tests were completed for each mesh. Field comparisons of 333- and 505-nm mesh nets were based on 

 492 bongo tows made in 1974 and 1975, which examined the number of larval winter flounder by 1-mm 

 size classes. Comparisons of 202- and 333-|j,m mesh nets were available from 28 bongo tows in 1984 and 

 were based on the sample densities of Stage 1 and eady Stage 2 larvae. The effect of tow duration on 

 sample density was made in 1984 with consecutive 6- and 15-min tows in the Niantic River using 333-nm 

 mesh nets (16 comparisons). A Wilcoxon signed-ranks test was used to compare the paired samples and 

 test for significant differences (p^0.05) due to mesh and tow duration. 



22 



