summary, the pattern revealed by the available catch data suggests 

 that yellowfin were centered over the Equator to the east of 150 W. 

 during February and March. Later in the year, during May and June, 

 they were centered north of the Equator to the west of 150°W. During 

 August they were centered in the general vicinity of 150°W. , and during 

 December they were scarce along 150°W. Whether these apparent 

 shifts in abundance are parts of a pattern of regularly recurring annual 

 migrations, or merely transient phenomena possibly associated with 

 changes in the environment during one year is a problem that remains 

 for future study. Some indication that the shifts may be manifestations 

 of a stable pattern, as yet poorly understood, is given by the repeated 

 occurrence of very good fishing along 150°-155°W. longitude during 

 August-September of 1951 and 1952 (Murphy and Shomura 1953a, 1955) 

 and again in 1953. 



Other Tunas 



The distributions of the other three tunas (bigeye, albacore, and 

 skipjack) differ from that of the yellowfin and among each other. For 

 instance, bigeye catches were sporadic and small in the vicinity of the 

 Equator, where yellowfin were most abundant (fig. 5). Generally big- 

 eye were most abundant north of 5°N. latitude, where yellowfin were 

 scarce. This is also shown in the results of Japanese fishing between 

 170°W. and 180° (appendix tables 12 and 13). It is worth noting that 

 bigeye are nowhere as abundant as yellowfin, high catches ranging from 

 2 to 5 per hundred hooks, whereas high yellowfin catches range from 5 

 to 15 per hundred hooks. 



Albacore, unlike both bigeye and yellowfin, were most abundant 

 south of the Equator (fig. 5) with the peak catch at 6°S. on 170°W. This 

 is in general agreement with the results of earlier cruises, when they 

 were found to be most abundant south of the Equator in the western port- 

 tion (170°W. -180°) of the survey area (Murphy and Shomura 1953b, 1955). 



Skipjack were taken sporadically in small numbers throughout 

 the entire area, usually not more than one or two at a station (appendix 

 tables & to 11). These catches can hardly be taken as more than an indi- 

 cation of the presence or absence of skipjack, for longlines do not sample 

 this small, surface-schooling species effectively. 



Relation of Catches to the Environment 



The 1953 longline surveys substantiate earlier findings (Murphy 

 and Shomura 1953a, b, 1955) on the relation of the distribution of deep- 

 swimming tunas to major features of the environment. In general 



