SUMRY AND CONCLUSIONS 



lo This report presents an analysis of 365 quantitative zooplankton 



collections obtained on seven cruises in Hav.-aiian waters during the 

 years 1950 to 1952 o 



2o The collections were taken by a variety of hauling methods? hori- 

 zontal hauls at several depths ranging from the surface to 300 

 meters ,s and oblique hauls to depths of 200^ 300,, and 500 meterso 



3o One type of net was used throughout^, a i-meter net with body of 

 30XXX grit gauzes rear section and bag of 56XXXo The net was 

 equipped with a flow meter which gave an estimate of the volume of 

 water strained o 



4« In the laboratory the displacement volumes of all samples were 



measured in uniform fashiono For each sample there was calculated 



the volume of the more nutritious zooplankton per unit of water 

 strained o 



5o For the tv;o cruises employing horizontal hauls „ the greatest 



zooplankton volumes occurred on the average at the 50-meter level 

 in both day and night samples o 



6o A 24-hour series of successive oblique hauls to 200^ 300j, and 



500 meters showed significant differences among depths and among 

 hauling times o A marked diurnal i/ariation in catch was found among 

 hauls to all three depths » 



7. A method is presented for adjusting the zooplankton volumes for 

 differences associated with diurnal variations in 'bJi© catoho Txie 

 method is based upon the similarity between diurnal -rariation in 

 zooplankton abundance in the upper 200 meters and the curve of the 

 sins function a with midnight equated to the angle vAose sine is 



/ loOo 



8o Geographically the abundance of zooplankton was remarkably uniform 

 throughout the Is lands o On the averages, however, the southeastern 

 region^ ioCo waters adjacent to the island of Hawaii yielded the 

 lowest zooplankton volumes u 



9o For the years 1950 and 1951 zooplankton samples collected in early 

 and midsummers during the skipjack season j, were significantly larger 

 than those taken in the late suinmer and fall after the close of the 

 seasoDo This decrease in the amount of zooplankton may bear seme 

 direct or indirect influence on the exodus of skipjack from Ha%vaiian 

 waters s although the decrease was certainly not of sufficient degree 

 to be a major or determining factor o 



51 



