net in the three-net series). All nets ha(J a 

 mouth (Jiameter ot 1 m. 



3. Sine-time a(Jjustments for variations in 

 volumes of zooplankton due to (Jiel variation 

 were made whenever possible. Corrections 

 were applied to the sampling depths in the three- 



Figure 17 . --Hydrographic stations at which 

 zooplankton was collected on HMS-34. 



net hauls by the use of correction factors com- 

 puted from depth-gage data. 



4. Zooplankton in the upper stratum of water 

 was, with one exception, greater in volume and 

 number of organisms than in the middle and 

 lower strata, regardless of the date or time of 

 day. 



5. Differences in average volumes of zoo- 

 plankton between windward and leeward areas 

 off Oahu were significant for the surface-to- 

 thermocline hauls of CHG-24 (November 14-18, 

 1955) and for the upper nets of HMS-34 (May 

 7-29, 1956). Differences between areas were 

 not significant for the middle and lower nets. 



6. Seasonal catches appeared to be different, 

 but their significance was clouded by some evi- 

 dence of annual variations. 



7. Copepods composed nearly one-half ot all 

 the organisms in the samples of zooplankton. 



8. The relative abundance of the various 

 groups of zooplankton remained comparatively 

 stable by depth and season. 



9. Decapod crustaceans were consistently 

 more abundant on the windward side than on the 

 leeward. 



10. Halosphaera viridis . a planktonic alga, 

 was very abundant at times. It made up 16 per- 

 cent of the total number of organisms in one 

 set of samples in the upper stratum of water. 



11. The following groups exhibited conspicu- 

 ous diel variations in abundance: polychaetes, 

 ostracods, calanoid copepods, euphauslids, am- 

 phipods. pteropods. and fish larvae. 



Figure 18. --Average volumes of zooplankton by cruise for each month in which samples were 

 collected, July 1951 to June 1956. Number of samples is shown in parentheses. (Data 

 for 1951-54 from fig. 7 in King and Hida, 1957.) 



19 



