SUMMARY 



1. The Pacific Oceanic Fishery Investigations conducted six longline 

 cruises in the equatorial region of the Pacific between 140 W. and 

 170 W. longitude during 1953. 



2. The catches experienced during the several crossings of the equa- 

 torial current system were consistent with earlier findings. 

 Yellowfin were found most abundant in the region near the Equator 

 which is enriched by upwelling. Bigeye were most abundant in the 

 region of the Countercurrent, and albacore most abundant south of 

 the Equator. 



3. The results suggest that the longitude of best catch shifted during 

 the year, and that east-west movements recur from year to year. 



4. Catches around Christmas Island were higher than in the open 

 ocean, at least in part because small "surface yellowfin" were 

 taken in addition to the large deep-swimming yellowfin. 



5. Yellowfin were usually taken in greater numbers on the deeper 

 hooks of the longline. Bigeye and albacore catches exhibited this 

 tendency more markedly than those of yellowfin. 



6. During 1953 more small yellowfin were taken near islands than 



offshore. The size of oceanic yellowfin was uniform from 140 W. 



to 160 W. longitude, but specimens from 170 W. were smaller. 



o o 



The size of the yellowfin taken at 150 -155 W. longitude did not 



change materially throughout the year. 



7. Males predominated among the larger yellowfin, bigeye, and 

 albacore. 



8. Short droppers (2-3 fathoms) appeared to be as efficient as long 

 branch lines (10 fathoms), except for a tendency to break more 

 often. 



9. The use of wire links in the mainline, to which branch lines are 

 attached, materially reduced the number of tangles. 



10. Increasing the number of branch lines on 1, 260 feet of mainline 

 from 6 to 1 1 increased the catch about 21 percent. This increase 

 was greater than the additional hauling time imposed by the added 

 branch lines. 



11. Shark damage to the tuna catch averaged 18.8 percent. 



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