years by juveniles. As areal distribution increased, concentrations in the lower river most Ukely decreased. 

 This confounds the use of an abundance index based on tows from only the lower river channel stations. 



Juvenile abundance data were also available from the trawl monitoring program for January through 

 April at the five stations outside the river. These CPUE values show generally uniform densities of 

 juveniles from 1976 through 1982 (Fig. 29). A sharp increase occurred in 1983 followed by a decline to 

 average levels in 1984 and 1985 and an increase to another peak in 1986. CPUE values were close in 

 magnitude to those determined for slightly shorter tows in all areas of the river during 1981-86. However, 

 the 1986 median was significantly greater than the values obtained for the lower river channel and for the 

 entire river. The low abundance in the river during 1986 may not be indicative of the true abundance of 

 the 1985 year-class, which may have been less concentrated in the river than others observed. Because of 

 the disparities among the various estimates, the relative abundance of juvenile winter flounder is known 

 with less certainty than that of adults, which are found mainly in the river during winter and early spring. 



Impingement 



Abundance 



Estimates of the number of winter flounder impinged on the traveling screens of MNPS are available 

 from 1972-73 through the present. With the installation of a fish return sluiceway at Unit 1 in December 

 1983, the the estimated total of 2,926 in 1984-85 was the second lowest of the 13-yr series (Table 29). 

 Most armual estimates for two-unit impingement ranged from 4 to 10 thousand, with an exceptionally 

 high estimate of 24,494 in 1978-79. Since 1976, it has been the second most abundant fish impinged at 

 MNPS, making up 8.4% of the total. If one large impingement event (over 400,000 on one day in July 

 1984) of sand lance {Ammodytes americanus) is ignored, the winter flounder would rank fu-st among all 

 fishes. About two thirds were impinged during winter and relatively few were taken in summer. 



Precision of winter flounder impingement estimates should have increased following 1982-83. Using 

 a resource allocation analysis suggested by El-Shamy ( 1979), the number of samples was changed from a 

 uniform number per month to a variable schedule, specifically reflecting the variability of winter flounder 

 impingement (NUSCo 1983b). More samples were taken in February and March and fewer in other 



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