CONTENTS 



Page 



Introduction 1 



Longline catch data 1 



Source of Data 1 



Evaluation of longline data 1 



Distribution of effort 4 



Relative abundance of skipjack tuna 4 



Distribution of catch per unit effort 4 



Salient features in the distribution of catches and catches per unit effort 5 



Adult-larvae relationship in the equatorial Pacific 18 



Movement of skipjack tuna in the Pacific 19 



Past studies on movement of skipjack tuna 19 



Movement of skipjack tuna inferred from present study 21 



Western Pacific 23 



Eastern Pacific 23 



Central Pacific 24 



Discussion 24 



Summary 28 



Acknowledgments 28 



Literature cited 28 



Figures 



1 . Geographical locations of skipjack tuna fisheries in the Pacific Ocean 2 



2. Length composition of skipjack tuna taken with pole-and-line and longline gear in various 

 parts of the Pacific Ocean 3 



3. Average quarterly effort expended by the Japanese tuna longline fishery, 1964-67 6 



4. Distribution of catch per unit effort of skipjack tuna taken by the Japanese tuna longline 

 fishery, 1964 8 



5. Distribution of catch per unit effort of skipjack tuna taken by the Japanese tuna longline 

 fishery, 1965 10 



6. Distribution of catch per unit effort of skipjack tuna taken by the Japanese tuna longline 

 fishery, 1966 12 



7. Distribution of catch per unit effort of skipjack tuna taken by the Japanese tuna longline 

 fishery, 1967 ■ 14 



8. Outlines of the northern and southern boundaries of skipjack tuna caught in the Japanese 

 tuna longline fishery, 1964-67, by quarters 16 



9. Catch rates of skipjack tuna larvae and adults across the Pacific Ocean between lat. 10°S 



and 20°N 19 



10. Range and migration routes of skipjack tuna of the western subpopulation 20 



11. Migration routes of skipjack tuna proposed by Naganuma (unpublished manuscript) based 



on tuna longline data 21 



12. Quarterly changes in position of high-CPUE areas in the Japanese tuna longline fishery, 

 1964-67 22 



13. Major circulation features of the Pacific Ocean 23 



14. Assumed movement of the various stocks of skipjack tuna in the Pacific Ocean 24 



15. Assumed routes followed by tagged skipjack tuna from the eastern to the central Pacific ... 27 



Tables 



1. Estimated ratio of skipjack tuna recorded to skipjack tuna landed in the Japanese long- 

 line fishery, 1962-67 3 



2. Probabilities (two-tailed) of differences in recording skipjack tuna caught on longline be- 

 tween small (20-50 tons) and large (50-200 tons) vessels by quarters (vessel sizes in gross 

 metric tons) 4 



3. Catch rates of larval skipjack tuna in night surface tows across the Pacific Ocean 18 



4. Skipjack tuna tagged in the eastern Pacific and recaptured in the central Pacific 25 



ui 



