ABSTRACT 



On six cruises around the Hawaiian Islands during 1953, 90 days were spent intensively 

 searching for skipjack (jiku) schools. Six flights in U. S. Navy PBY amphibians were also made. 

 The purposes were to evaluate and improve the scouting techniques and to determine the distri- 

 bution of the skipjack. 



Skipjack schools are located almost entirely by accompanying birds which flock and 

 maneuver characteristically when working over thenn. Flocks are seen out to 4 miles from the 

 vessel, but most are seen within 2 miles. A new method of estimating the scanning efficiency 

 indicates that only 6 percent of total flocks are seen beyond 2 miles, and 38 percent between 1 

 and 2 miles. Many flocks were missed. Careful scanning aft of the vessel on autumn cruises 

 resulted in a 22 percent increase in number sighted. 



Numerous factors affecting the occurrence of flocks and the methods of sighting them 

 were investigated. Poor weather conditions reduced the proportion of flocks seen. Large flocks 

 were seen farther from the vessel than small ones. Fishermen maintain consistent watches and 

 are good at estimating distances. In April more flocks were seen in early morning and mid- 

 afternoon: in June more just before noon and in the autunnn they were randomly distributed during 

 the day. 



Airplane scouting is much less effective than vessel scouting, probably because the dark- 

 colored birds cannot be seen against the water. 



The Hawaiian fleet catches three-fourths of its skipjack within 20 miles of land, but 

 schools are not more abundant there. There was no decline in abundance with distance from 

 land out to 230 miles northeast and 350 miles southwest of Oahu. 



More schools were seen southwest of Oahu in February, September, October, and 

 November^ more to the northeast in April and June. 



One location, near an eddy, contained much larger numbers of schools during the Sep- 

 tember and October cruises. This eddy may enrich the waters, and it will be studied much more 

 intensively. 



A peak in the seasonal cycle of number of schools seen occurred in A'pril, not when the 

 catch was greatest in June to August. It is shown that the schools observed in April contained 

 smaller fish and the fishermen fished fewer of them. 



