for each sample. Net mesh size was 333 [im, 

 except for a period from mid- February through 

 March, when 202-|im mesh nets were used to 

 reduce the extrusion of yolk-sac winter flounder 

 larvae (see Winter Flounder Studies section). 



Plankton samples were split using a NOAA- 

 Boume splitter (Botelho and Donnelly 1978) and 

 sorted for ichthyoplankton using dissecting mi- 

 croscopes. Successive splits were completely 

 sorted until at least 50 larvae and 50 eggs (for 

 samples processed for eggs) were found, or until 

 one-half of the sample was examined. Samples 

 sorted for larvae included all those from FN col- 

 lected during .January through May and .July 

 through December, one day and one night sample 

 collected per week during .June, and all NB sam- 

 ples. Three day and three night FN samples 

 collected in April through September were sorted 

 for fish eggs. Fish eggs and larvae were identified 

 to the lowest practical taxon. Gunner and tautog 

 eggs were differentiated from a weekly composite 

 sample of their eggs using the criterion of 

 bimodality of egg diameters (Williams 1967). 

 Ichthyoplankton density was expressed as number 

 per 500 m" . Included in this report are 

 ichthyoplankton data through May 1987, starting 

 with egg collections at EN in May 1979; larval 

 collections at EN in January 1976 and at NB in 

 .January 1979. 



Data analyses 



To assess impacts it was necessary to identify 

 potentially affected species, document their spatial 

 distribution, and describe the natural temporal 

 fluctuations of their life history stages collected 

 near Millstone. The selection of potentially af- 

 fected species was based on their prevalence in 

 entrainment or impingement samples or their 

 abundance in the shore-zone area of .Jordan Cove, 

 an area which may be impacted by the thermal 

 plume. Indices to describe temporal and spatial 

 abundance for all life history stages of fishes must 

 be selected based on the knowledge of the under- 

 laying assumptions of each index. Failure of the 

 data to conform to these assumptions may reduce 

 the precision of the estimates or, worse, provide 



invalid results. Since fisheries data typically have 

 numerous zero values and follows a lognormal 

 distribution, the 5-mean (Pennington 1983, 1986) 

 was used as the index of abundance of various 

 life history stages of selected species. A detailed 

 description and evaluation of this statistic is pro- 

 vided in a separate section (see Delta Distribution 

 section). The S-mean was used as an index of 

 abundance for juveniles and adults collected in 

 the trawl and seine programs and for larvae that 

 were not consistently collected during their sea- 

 sonal occurrence. For species that were collected 

 seasonally, the data used to calculate the 5-mean 

 were restricted to the period of occurrence to re- 

 duce the number of zero values. An alternative 

 index of abundance, used for ichthyoplankton 

 that were collected consistently during their sea- 

 sonal occurrence, was the a parameter from the 

 Cjompcrtz function (Draper and Smith 1981). 

 Typically, the distribution of ichthyoplankton 

 abundance over time is skewed, with a rapid in- 

 crease to a maximum followed by a slower decline. 

 This skewed density distribution results in a 

 sigmoid-shaped cumulative distribution and the 

 time of peak abundance is the time at which the 

 inflection point occurs in the cumulative distribu- 

 tion. The Gompertz function was chosen to de- 

 scribe the cumulative distribution data because 

 the inflection point of this function is not con- 

 strained to the central point of the sigmoid curve. 

 'I'he form of the Gompertz function was: 



C,= a(exp[-pe"'''l) 



where Q = cumulative density at time t 



a = total or asymptotic cumulative 

 density 



P = location parameter 



K = shape parameter 



t = time in days 



The origin of the time scale was arbitrary and 

 for our data was set to the time of the year that 

 the respective developmental stage generally starts 

 to appear in ichthyoplankton samples. Least- 



258 



