■ earlier J, this portion of the sample was examined under 

 the microscope and classified as to its make-up^ whether 

 of average (mixed) compositions, composed primarily of a 

 swarm of one organism^ or containing an unusual amount of 

 nonnutritious forms o 



(2) All annelids, crustaceans ^ cephalopods, and fish in the 

 2 to 5 cm„ size category „ 



The following organisms in the 2 to 5 cmo category 

 were not included as foods siphonophoresj, medusae « 

 ctenophores, heteropods^/j, and tinioateso 



The sum of items (1) and (2) provided a single vol\uns measure- 

 ment for each san^le which we accepted as the best available estimate 

 of the amount of zooplankton -- as food — presenx at that time and place 

 and subject to capture by the gear employedo 



"'/ERTICAL AND DIURNAL VARIATIONS 



The collections resulting from cruises 4 and 6 of the Hixgh Ho 

 Smith provide information of interest on the vertical distribution of 

 zooplanktono The chief purpose of these two cruises was to investigate 

 the time and extent of tuna spawning in Hawaiian waters » A sampling plan 

 to examine horizontal and vertical v8.riations in the abundance of tuna 

 eggs and larvae was carried out at each stations with meter-net hauls 

 being made simultaneously at three levels; Oj, 50^, and 150 meters i 0„ 

 100, and 200 metersi or 0, 150, and 500 meters o There was no means of 

 closing the nets while they were being lowered and raised^ but the per- 

 centage of towing time during this phase of the haul was small and is 

 not likely to have affected greatly the results o It was not possible to 

 hold the ship's speed constant throughout the haul nor to change the 

 spacing of the nets on the towing wire once the haul had started o There- 

 fore the nets were not alvrays at the intended deptho fte believe^ how- 

 ever, from calculations based on virire angle and meters of wire out that 

 the actual towing depth ordinarily did not -^rary by more than ± 20 percent 

 of the desired deptho 



The data were classified into day^, nighty, and t^yvilight hauls 

 on the criteria of times of sunrise^ sunset^ and the beginning and end of 

 twilight periods as defined by the American Nautical Almanac o Averages 

 were calculated for zooplankton volumes obtained at each haul level and 

 the day collections vere compared with the night collections o The 



T/ Bigelow and Sears (1939) and also Clarke (1940) considered the ciusta- 

 ~ ceanss chaetognaths , and molluscs as being of high nutritive valueo 

 It was our judgment, howeverj that the heteropod molluscs of the fam- 

 ily Pterotracheidae, which are of common occurrence in the planlcton 

 of the tropics and subtropics of the Pacific ^ do not belong with 

 this group because of their watery structure and should be classed 

 with the nonnutritious forms <> 



