The sampling dates were spaced over most of the larval winter flounder season to collect various devel- 

 opmental stages. In 1984, mostly Stage 1 and 2 larvae (92%) were collected on April 5 and on May 8 

 the larvae were primarily Stage 3 (85%). In 1985, all larvae collected on March 28 were Stage 1 and 2, 

 on April 29 most were Stage 2 and 3 (99%), and on May 28 Stage 3 was dominant (89%). A few Stage 

 4 larvae were collected on two of the sampling dates (May 8, 1984 and May 28, 1985). Examination of 

 the combined data from all five dates by percent occurrence of each developmental stage showed that 

 Stage 1 and 2 larvae were more abundant during ebb tides and Stage 3 and 4 during flood tides (Fig. 23). 

 Similarly, examination by size classes showed that larvae 4 mm and smaller were more abundcint during 

 an ebb tide and larvae 5 mm and larger were more abundant during a flood tide. 



In order to determine if velocity measurements were comparable between ebb and flood tides, separate 

 quadratic polynomial equations were fitted to hourly velocity measurements combined from each of the 

 five ebb and flood tides sampled. Good fits were obtained with an R value of 0.96 for both equations. 

 The mean ebb duration was 6.8 h and flood duration was 5.8 h. The area under the curve for the flood 

 tide (299.6) was smaller than for the ebb tide (397.7), indicating that flood velocities were low due to 

 sampling location. To make ebb and flood velocities comparable, the flood velocities were estimated using 

 a technique presented in NUSCo (1986a). The calculations of net exchange of larvae which follow were 

 based on actual ebb current velocities and the adjusted flood current velocities. 



Using data combined from the five sampling dates, net tidal exchange was estimated for each 1-mm 

 size-class. The estimates were obtained by summing the number per 500 m of larvae of each size-class 

 in each hourly sample for the five sampling dates. The sum was multiplied by the estimated water velocity 

 at the time of the hourly collection. This density-velocity adjustment accounted for changes in discharge 

 volume during the tidal cycle. Because larvae coUected during an ebb tide represented a loss from the 

 river, the density- velocity value was made negative. A harmonic regression equation using a 12.6-h tidal 

 cycle (the average duration of the five tides sampled) was fitted to density-velocity values. The area under 

 the curve for each tidal stage was estimated by numerical integration of the regression equation using 

 5-min increments. Net tidal exchange was expressed as the percent return of a size-class on a flood tide 

 compared to loss on a ebb tide (Table 27). The harmonic regression could not be fitted to the 2-mm 

 size-class, because so few were collected on a flood tide. The results showed a net export of 4 mm and 

 smaller size-classes and a net import of 5 mm and larger size-classes. 



