o 

 o 



Figure 7. --Mean zooplankton volumes by cruise for each month of sampling 

 during the period July 1951 - August 1954. Nunnber of samples is shown 

 in parentheses. 



others were greatly limited in scope, but the 

 localities sampled were thought to be repre - 

 sentative of the region. Perhaps the naost out- 

 standing feature of the data is the uniformly 

 low average volumes obtained in 1953. Sam- 

 pling conducted during 8 months of that year 

 revealed a persistent low level of plankton abun- 

 dance, broken only in the month of June. • 



Although our sampling was also inade- 

 quate for a seasonal comparison, when data for 

 like months are combined the results (fig. 8) 

 show a trend of increasing zooplankton abun - 

 dance from March to July. Following July, the 

 average volunaes became quite variable. Un- 

 fortunately we have no plankton data for the 

 months of January, February, and December. 



In his study of the chennical and physi- 

 cal properties of Hawaiian waters, Seckel (1955) 

 stated that he could discern no definite seasonal 

 cycle in temperature or salinity as observed on 

 one winter and two summer cruises. The sea- 

 sonal range in temperature was about 4*F. 

 which was less than the range which nnight be 

 encountered on any one cruise as the result of 

 geographical variations. So it is perhaps not 

 surprising that we found no marked seasonal 

 variation in zooplankton abundance. 



As judged by the catch of the Hawaiian 

 pole-and-line fishery (Y a nn a s hi t a 1957), the 

 abundance of skipjack varies greatly with sea- 

 son, the bulk of the catch, on the average, being 



obtained during the months of June, July, and 

 August (fig. 8), Although we obtained the high- 

 est average volume of zooplankton in July that 

 month was sannpled in only one year; moreover, 

 the differences between months throughout the 

 year were slight as compared with the wide vari - 

 ation in fish catch. Although there is a rough 

 seasonal correspondence between zooplankton 

 abundance and water temperature (fig. 8), we 

 must conclude that, when our data are summa- 

 rized as in figure 8, there is little evidence of 

 any causal relationship or close covariation be- 

 tween zooplankton and surface temperature or 

 zooplankton and skipjack catch. 



CORRELATIONS WITH 

 ENVIRONMENTAL FACTORS 



Despite evidence of great uniformity in 

 both the biological and the physical and chemi- 

 cal environment, we thought it worthwhile to 

 examine the degree of correlation of zooplank- 

 ton catch and certain factors considered most 

 likely to have biological significance. The re- 

 sults from three nnajor cruises, summarized in 

 table 4, show lack of significant correlation be- 

 tween zooplankton volumes and temperature tat 

 10 meters depth), surface inorganic phosphate— 



— The temperature and phosphate data em- 

 ployed in these statistical tests have been pub- 

 lished in reports of McGary (1955) and Seckel 

 (1955). 



10 



