in appearance and the overlapping ranges of their 

 diameters (Matsumoto, 1958). 



This report presents information on the abundance 

 and distribution of larval tunas in the region of the 

 Marquesas Islands. Six species of larval tunas were 

 identified, but emphasis is on skipjack, as it occurred 

 more often than the others. Inferences concerning 

 skipjack spawning are compared with those derived 

 from ovarian studies of this species from the same 

 area (Yoshida, 1965). 



COLLECTION OF SAMPLES 



Plankton samples from which the larval tunas 

 were sorted and counted were collected from research 

 vessels of the Bureau of Commercial Fisheries in 

 1957 and 1958 on a standardized offshore survey 

 pattern and at a diel variability station (fig. 1). The 

 latter was situated at lat. 9°34' S. and long. ISg'SO' 

 W. (about 15 miles southeast of the island of Hua 

 Pou) and was occupied for 24-hour periods on six 

 occasions. Cruises, dates, and numbers of samples 

 obtained on the offshore surveys and at the diel 

 variability station are summarized in tables 1 and 2 

 respectively. Fishery and environmental data col- 

 lected on these cruises have been published by 

 Wilson, Nakamura, and Yoshida (1958). 



Plankton hauls were made with a net having a 

 mouth diameter of 1 m. The net was constructed 

 of nylon netting with mesh apertures of O.GG mm. in 

 the body and 0.31 mm. in the rear and cod end (for 

 details of construction and dimensions, see King and 

 Demond, 1953). A flowmeter mounted in the cen- 



T.\BLE 1. — Cruises, dates, and numbers of zooplankton samples 

 obtained on offshore surreys [C // (7 = Charles H. Gilbert, 

 H MS = Hugh M. Smith] 



Table 2. — Cruises, dates, arid numbers of zooplankton samples 

 obtained at the diel variability station [C//G = Charles H. 

 Gilbert, //.'l/.S = Hugh M. Smith) 



ter of the motith provided estimates of the amount 

 of water strained. 



Oblique, open-net, J^^-hour plankton hauls from 

 the surface down to 140 m. and back to the surface 

 were taken during the offshore surveys and at the 

 diel variability station on all cruises. A second net 

 was attached to the towing cable to permit sampling 

 between 140 antl 280 m. at tiie diel variability station 

 on Hugh M. Smith cruise 45 (HMS-45). This latter 

 net was similar to the open one but was modified to 

 permit attachment of opening and closing devices 

 (King, Austin, and Doty, 1957). 



Two consecutive } 2-hour tows were made during 

 Charles H. Gilhvrl cruise 35 (CHG-35) to obtain data 

 for testing the duplicability of the catches. 



On the offshore surveys, plankton hauls were made 

 twice eacli night, once before midnight (between 

 2000 and 0000 hours) and once after midnight (be- 

 tween 0200 and 0400 hours). At the diel variability 

 station, duplicate hauls were made every 3 hours on 

 CHG-35, while single hauls were taken at 2-hour 

 intervals on the other cruises. 



Plankton samples were preserved in 10 percent 

 Formalin.' 



In the lal)oratory all fish and fish eggs were sorted 

 from plankton samples with the aid of binocular dis- 

 secting microscopes. From these collections of fish 

 and eggs, larval tunas were separated and identified. 

 Most of the larvae were less than 5 mm. in total 

 length. Specimens greater than 10 mm. comprised 

 a very small percentage of the total number. 



TREATMENT OF DATA 



Larval abundance is expressed as the number of 

 larvae in a column of water 10 m. sc[uare and 140 m. 

 deep. This value was obtained by multiplying the 

 numl)er of larvae per cubic meter of water strained 

 by tlie volume of the column of water. 



Nonparametric statistics (Siegel, 1956) were used 

 in our analyses to avoid assumptions of normal 

 distributions. 



Data on plankton hauls and numbers of larval 

 tunas collected at the diel variability station and on 

 the offshore surveys are presented in appendix tables 

 A-1 through A-8. 



DUPLICABILITY OF CATCHES 



Catches of larval tunas by successive tows were 

 compared by Strasburg (1960). He found no sig- 



' Trade names referred to in this publication do not imply endorsement 

 of commercial producU. 



U.S. FISH AND AVILDLIFE SERVICE 



