Some experimental gear was fished on each of the six cruises 

 in 1953 in order to determine whether modifications of the standard 

 gear would decrease the labor of handling the gear or increase the 

 catch per unit of gear. The details of each type of special gear and the 

 results from its use will be discussed in a separate section: the dis- 

 cussions of distribution and abundance are based on the standard gear 

 described above. 



The daily operations during the 1953 cruises were similar to 

 those of earlier cruises. Setting started at dawn and took a little over 

 an hour. Either fresh frozen sardines or herring were used as bait. 

 Hauling commenced around noon, and the last basket set was the first 

 to be hauled. Although the total time taken for hauling differed some- 

 what from station to station, the line was usually all on board at about 

 4:30 p.m. Further details of the work schedule for each station of the 

 several cruises are given in appendix tables 22 through 27. 



DISTRIBUTION AND ABUNDANCE OF TUNAS 



The fishing cruises prior to 1953 were designed to cover a wide 



o o 



expanse of the equatorial Pacific (180 -120 W. longitude) in order to 



delimit the general area in which yellowfin were most abundant. 



o 

 These surveys revealed a zone of high abundance between 140 W. 



and 160°W. longitude (Murphy and Shomura 1953a, b, 1955). Within 



these longitudes yellowfin were most abundant in the latitudinal belt 



enriched by the equatorial upwelling described by Cromwell (1953), the 



best catches usually being made between 1 N. and 6 N. latitude. 



During 1953 attention was focused on a narrower range of longi- 

 tudes (140 W. to 170 W.) in order to study more effectively latitudinal 

 and seasonal variations in yellowfin abundance in the most promising 

 area. In addition, special studies were made of the tuna populations in 

 the vicinity of the Line Islands (fig. 1). 



In our discussion, the longline stations for 1953 are separated 

 into two categories, oceanic and insular, the latter being those located 

 within 80 miles of land. This separation, in part arbitrary, was made 

 in order to determine whether the abundance and the size of longline 

 tuna are related to the nearness of land. The line of demarcation 

 chosen probably eliminates the influence of the islands from the oceanic 

 stations, as it seems unlikely that the presence of the small Line 

 Islands significantly alters the environment for tuna as far as 80 miles 



