and depth to the top of the thermocline. This 

 lack of correlation with the fields chosen may 

 be of significance in itself, and would seem to 

 indicate that other, more fundamental factors 

 of the environment may be the causative agents 

 for the variations observed. 



During the period April - December 195 3, 

 four "permanent" stations between Oahu and 

 Molokai were visited at approximately weekly 

 intervals with sampling of zooplankton (at three 

 of the stations only), temperature, phosphate, 

 and salinity, for the purpose of following detailed 

 changes in the environment associated with the 

 opening of the skipjack season in the early sum- 

 mer months and the decline in the catch during 

 the fall. It was assumed that these selected lo- 

 cations would yield data fairly representative of 

 conditions throughout Hawaiian waters. 



The northernmost station, station A (fig. 

 4). was positioned so as to san-iple "open ocean" 

 water to the windward of the islands, station B 

 to sample channel water, station C to sample 

 water over Penguin Bank where the depth ranged 

 fronn 50 to 100 meters, and station D the open 

 ocean to the leeward of the islands. Station A 

 was normally visited at about 1300, station B at 

 1900, station C at 2300, and stationD 0300 hours. 

 At each station where depth of water permitted, 

 samples were taken between and 250 or 300 

 nneters (600 nneters on Smith cruise 21) for sa- 

 linity and phosphate measurements. Surface 

 tennperatures were taken with a bucket, thermo- 

 meter; subsurface temperatures were recorded 

 with a bathythermograph. Only the surface data 

 are utilized in this report, however. 



cooler on the average than station D. Corre- 

 lation analyses based on the repeated observa- 

 tions made at station D, summarized in table 5, 

 showed no significant correlations between zoo- 

 plankton volume and surface temperature, sur - 

 face inorganic phosphate, thermocline depth, 

 surface salinity, and the weekly skipjack catch 

 for the Hawaiian area. 



If we replot the temperature and zoo- 

 plankton data obtained at station D during the 

 early weeks (April - June) of the survey, to- 

 gether with the skipjack catch for the entire 



Hawaiian area for the same period, we find an 

 interesting covariation {fig. 10). Warming of 

 the water in early April was accompanied by an 

 increase in zooplankton and in catch of skipjack. 

 Subsequent cooling about the nniddle of Apri 1 

 was associated with a drop both in zooplankton 

 and skipjack catch. As the tennperature in- 

 creased during May and June there was again a 

 corresponding general increase in zooplankton 

 and skipjack abundance. We are not able to 

 define the causative factors in this sequence of 

 events. The correlation coefficients for surface 

 temperature and zooplankton (r = 0. 385) and for 

 skipjack and zooplankton (r = 0.593) were below 

 the 5-percent level of significance (r q^ = 0.602). 

 Surface temperature and skipjack, however, 



showed a highly significant correlation (r = 

 0.777), beyond the 1 -percent level of signifi- 

 cance (r Q, = 0.735). It is possible that none of 

 the factors examined are directly related, but 

 that all exhibit chance variations, or that all 



are governed by changes in the general circula- 

 tion or Sonne other basic, underlying condition 

 in the environnnent as yet undetermined. 



Plankton hauls were made at station B on 

 only one cruise. The 3 samples obtained at this 

 locatio.n on Smith cruise 21 averaged 13.2 

 cc. / 1000 m. . The 19 successful hauls made at 

 station C on Penguin Bank, which were shallow 

 tows between the surface and 40 or 50 meters 

 depth, yielded an average volume of 29.3 

 cc. / 1000 m. . This mean had considerably 

 higher variance than the means for station A 

 (16.2 CC./1000 m. ■^) and station D (19.4 

 cc. /lOOO m. ), both the latter stations being in 

 deep water and sampled with 0- to 200-meter 

 oblique hauls. 



When the various observations obtained at 

 stations A and D are plotted as in figure 9, we 

 obtain a connplex and confusing picture of rapid 

 fluctuations in the environment with no definite 

 seasonal trends and with very little agreement 

 between the two stations. Surface temperatures 

 of the two localities varied in somewhat parallel 

 manner, however, with station Abeing about 1*F. 



SUMMARY 



1. In this second report of the Pacific Oceanic 

 Fishery Investigations on variations in zoo- 

 plankton abundance in Hawaiian waters, we 

 summarize the results of plankton hauling 

 on 10 cruises during the years 1953 - 54. 

 Data from earlier cruises, included in a 

 previous report (King and Hida 1954) were 

 also utilized to some extent in drawing con- 

 clusions. 



2. The collections were obtained with 1-meter 

 nets of 30XXX grit gauze (aperture widths 

 0.65 mm.). Oblique hauls to about 200 

 meters' depth were employed at most sta- 

 tions. The results from a short series of 

 0- to 100-meter hauls are also included. 



3. The displacement volumes of all samples 

 were measured in the laboratory. For each 

 sample there was calculated the volume of 



12 



