The Pacific Oceanic Fishery Investigations (POFI) is conducting a survey of the 

 fishery resources of the centrad Pacific. Early in its program it became apparent that the various 

 species of tuna in this area represented a potential source of raw material for the American can- 

 ning industry. Further study showed that the deep-swimming tunais, particularly the yellowfin, 

 which may be caught by longline, were the nnost immediately available, and furthermore, the re- 

 source appeared to be large enough to support a substaintial fishery. Studies were then initiated 

 to determine the magnitude of the resource, its geographical distribution throughout the year, and 

 the environmental factors that control distribution and abundance. Included in this prograjn was^ 

 a series of longlining cruises which were to cross the equatorial region between 120 W, and 180 

 longitude. 



Two previous reports (Murphy and Shomura 1953a, b) cover the results of longline 

 fishing from July 1950 to June 1952. The present report includes the results of four cruises to 

 equatorial waters during the period August to November 1952. The catches are examined in re- 

 lation to the environment, and a summary is given of the geographical and vertical variation in 

 the catch rates. In connection with geographical variation a summary is given of selected Japa- 

 nese commercial fishing catches. There is included a resume of the size distribution of longline- 

 caught yellowfin and bigeye tuna across the equatorial Pacific, and an analysis of the sex ratios 

 of the yellowfin tuna. Finally, certain topics of particular interest to commercial fishermen, 

 such as gear design and shark damage are briefly discussed. The summarized field data from the 

 four cruises appear in the appendix. 



We use the common names of the fishes throughout this report. These, with their 

 commonly accepted scientific names, are as follows: 



White-tipped shark, Carcharinus longimanus (Poey) 



Silky shark, Carcharinus sp._^/ 



Great blue shark, F>rionace glauca (Linnaeus) 



Bonito shark, Isurus glaucus (MuUer and Henle) 



Marlin, Makaira sp . 



Sailfish, Istiophorus orientalis (Schlegel) 



Wahoo, Acanthocybium solandri (Cuvier and Valenciennes) 



Dolphin, Coryphaena hippurus (Linnaeus) 



Yellowfin tuna, Neothunnus macropterus (Tennminck and Schlegel) 



Bigeye tuna, Parathunnus sibi (Temminck and Schlegel) 



Skipjack, Katsuwonus pelamis (Linnaeus) 



Albacore, Germo alalunga (Bonnaterre) 



Lancet fish, Alepisaurus sp . 



Barracuda, Sphyraena barracuda (Walbaum) 



Several persons were responsible for the execution of the fishing cruises. Included 

 among the field parties were T. S. Hida, I. I. Ikehara, W. M. Matsumoto, D. L. McKernan, T. 

 Otsu, T. J. Roseberry, and W. F. Royce. Considerable assistance in the planning of the cruises 

 was rendered by O. E. Sette. The successful completion of the fishing was due in no small part 

 to the cheerful cooperation of the officers and fishermen of the three vessels. T. S. Austin and 

 the writers prepared the temperature profiles. Wilvan Van Campen translated the Japanese com- 

 mercial catch data, and Jean Hailing assisted in processing the catch records. 



MATERIAL AND METHODS 



The four cruises included in this report are (1) John R. Manning cruise 12, with lines 

 of fishing stations across the Equator on 140 W. and 150 W. longitude; (2) Cavalieri cruise 1, a 

 semicommercial fishing trip (McKernan 1953), with a line of stations fished south from 9 N. on 

 140°W. to the Equator followed by a series of stations north of the Equator between 140 W. and 



1/ A species closely resembling C. floridanus Bigelow, Schroeder, and Springer, and C. ahenea 

 ~ (Stead). 



