nearly the same to present. The major change was the use of Discharge 

 samples (0. 333-mm-mesh) rather than the Intake samples to determine the 

 species composition and estimate entrainment densities. The higher 

 water velocity at the Discharge provided more accurate sample volume 

 estimates and reduced the possibility of net avoidance by zooplankton. 

 Normandeau Associates, Inc. conducted zooplankton entrainment sampling 

 from July 1975 through December 1976. In 1975, one sample from the 18 

 weekly ichthyoplankton samples (0. 333-mm-mesh) was used for zooplankton 

 identification and enumeration. Alternate day and night weekly samples 

 were processed. In 1976 to the present, a day and night sample from 

 each week was processed for zooplankton. NUSCo staff conducted the 

 zooplankton entrainment program from 1977 to the present. Zooplankton 

 entrainment studies, since mid 1975, have provided a long time series of 

 quantitative data on the densities of entrained zooplankton. 



The ability of the present entrainment zooplankton program to 

 detect changes in annual abundance was examined with power curves (EROL 

 1982). The power of a statistical test, used in testing differences in 

 means, is the probability of detecting a specified difference between 

 means. Power curves were calculated for eight dominant zooplankton taxa 

 with paired comparisons of years 1976 through 1980 (total of ten compari- 

 sons for each taxa). Calculations were based on log.. n transformed data 

 with a two tailed test at <* = 0.05. For each of the taxa, the power 

 curves were almost identical for the ten paired comparisons of years 

 1976 through 1980. The 1979-1980 comparison is presented (Figure 3). 

 The detectable difference at a power of 0.80 was determined from the 

 power curves (Figure 3) and compared to yearly entrainment sample means 

 (mean of log.. n transformed data) . The detectable difference was examined 



10 



