VARIATIONS IN ZOOPLANKTON ABUNDANCE IN 

 HAMIIAN WATERS. 1950-52 



One of the major projects in the research program of tlie Pacific 

 Oceanic Fishery Investigations of the Fish and Wildlife Service is to ob" 

 tain information on the relative or potential productivity of different 

 areas of the tropical and subtropical Pacific o As indexes to productiT-ity 

 we have considered the oceanic circulatioHj, the concentration of a chemcal 

 nutrient (inorganic phosphate), the amount of dissolx'-ed oxygen, and the 

 abundance of zooplanktono 



The purpose of this report is to present the results of our zoo- 

 plankton sampling in -waters adjacent to the main or windward islands of the 

 Hawaiian archipelago „ fie shall consider how the abundance of zooplankton 

 varied geographically and in time during the period of study and to what 

 extent these variations were related to hydrographic conditionso The data 

 contribute information on vertical distribution and diurnal variation in 

 zooplankton abundance and indicate differences in relative productivity be- 

 tween the Hawaiian area and other regions of the central Pacifico 



Zooplankton is essential fish food. It is important in the food 

 of juvenile tunas and also occurs in wide variety in the food of adult tunas 

 (Reintjes and King 1953) o The bulk of the zooplankton, however^ reaches 

 the tunas — the group of fish presently vmder study by these investiga- 

 tions -- through the intermediary forage organisms, such as squid., shrimp, 

 and small fisho The standing crop of zooplankton is rather easily measured 

 in quantitative fashion and, we believe, is a reliable index to available 

 food. 



Although the primary aim of our plankton sampling was to obtain 

 information on the zooplankton population, a secondary objective was to 

 collect tuna eggs and larvae for use in the study of the spawning habits 

 of t\m&}y„ Sampling gear and procedures, therefore, were utiliasd which 

 would contribute toward both objectives » 



These collections constitute the first comprehensive survey of 

 zooplankton abundance in the offshore waters of the Hawaiian Islands o 

 Sampling of the offshore waters heretofore was limited to occasional hauls 

 made by the various oceanographic expeditions crossing the Pacifid, In 

 1875 the Challenger made surface hauls at a few stations close to the is- 

 lands (Murray 1895), In 1902 the U. S. Fisheries Steamer Albatross occupied 

 a number of stations in the Hawaiian area, at which surface plankton hauls 

 were made (V^ilson 1950) « Y.Tien the Carnegie visited the Islands in 1929, 



1/ This will be the subject of a separate report by other staff members 

 of POFIo 



1 



