reasons. Many small fishes pass through the collection basket drain 

 holes ( > 3/4" diameter). To demonstrate the effect of this bias, the 

 mean length of each major fish and invertebrate taxa sampled during 

 routine impingement was compared to the mean length based on samples 

 taken concurrently (December 1981 - April 1982) for a special impingement 

 study (NUSCo 1981b). In the special study, a 3/8 inch (9 mm) mesh net 

 was used to collect impinged organisms. Results showed large differences 

 in mean length between the two data sources for most species reflecting 

 a general skew in mean length towards the larger sizes (Table 7) . 



Further, during periods of high debris loading, commonly in the 

 spring and fall, the baskets clog quickly resulting in loss due to 

 overflow. Occasionally samples are terminated prematurely due to unsche- 

 duled dumping of the debris by operations and/or maintenance personnel. 

 Inadvertant disposal of trash to the land-fill site has also occurred. 

 And finally, plant personnel searching for food, bait, or just the 

 desire to return live specimens to the water before they die, has likewise 

 resulted in short counts. 



Through improved communications, plant management and personnel are 

 now more cognizant of our need for accurate samples. Unscheduled dumping 

 or disposal of trash has been reduced. Intrusions by plant personnel 

 have been eliminated. 



To correct for loss of organisms through the drain holes or through 

 overflow would require smaller apertures (minimum 3/8" mesh) in the 

 collection baskets at both units and shorter sample periods during times 

 of heavy debris loading. The additional effort required many not be 

 warranted at this time for Unit 1 since a sluiceway is being installed 

 at that unit. The extent to which data at Unit 2 are effected by this 

 bias, however, may be of future concern. 



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