DISTRIBUTION, APPARENT ABUNDANCE, AND LENGTH COMPOSITION 



OF JUVENILE ALBACORE, Thunnus alalunga, 



IN THE SOUTH PACIFIC OCEAN 



Howard 0. Yoshida' 



ABSTRACT 



The distribution, apparent abundance, and length composition of juvenile albacore, Thunnus alalunga, 

 were deduced from 127 specimens found in the stomachs of 2,297 billfishes collected in the South Pacific 

 between January 1964 and July 1966. Juvenile albacore were found in the South Pacific from lat 5° to 

 31° S, between long 153° and 179° W. Billfish stomach samples were collected from as far east as long 

 135° W, but juveniles were not in the stomachs east of long 153° W. The juveniles were consistently 

 more numerous between lat 10° and 20° S than in the area farther north. The mean length of the ju- 

 veniles increased from north to south but not from east to west (or vice versa). A southward migra- 

 tion of juveniles is postulated. 



In April 1963, the National Marine Fisheries 

 Service (formerly the Bureau of Commercial 

 Fisheries) , Hawaii Area Fishery Research Cen- 

 ter established a field station in Pago Pago, 

 American Samoa, to collect information on the 

 longline fishery based there. A fleet of vessels 

 from Japan, the Republic of Korea, and the Re- 

 public of China has supplied two American- 

 owned canneries with albacore, Thunnus ala- 

 hinga, and other tuna. In 1965 the fleet was 

 composed of 154 vessels which landed 15,588 

 metric tons of albacore (Otsu and Sumida, 1968) . 



The field station was established primarily to 

 study the eff'ects of the fishery on albacore. As 

 part of this study an investigation was started 

 to determine the early life history of albacore 

 in the South Pacific. 



Beginning in 1964, arrangements were made 

 with several longline fishing vessels based in 

 American Samoa to collect stomachs of billfishes, 

 which are known to prey on juvenile tunas (Yo- 

 shida, 1965, 1968). The distribution, apparent 

 abundance, and length composition of juvenile al- 

 bacore, here defined as fish smaller than 400 mm 

 standard length, were determined by specimens 

 found in the stomachs of the predators. 



MATERIALS AND METHODS 



The longline vessels based at American Samoa 

 fished primarily for albacore; billfishes were 

 taken only incidentally. The crews of the co- 

 operating longline vessels collected 2,297 bill- 

 fish' stomachs between January 1964 and July 

 1966. These stomachs were also used in a study 

 of juvenile skipjack tuna, Katsuwonus pelamis 

 (Yoshida, 1971). 



In the laboratory, all the tunas and tunalike 

 specimens were first sorted from the stomach 

 contents. The juvenile tunas were identified by 

 the use of skeletal characters; juvenile albacore 

 were easily identified by their definitive skeletal 

 characters (Matsumoto, 1963; Yoshida, 1965). 

 Standard length (SL) was taken for all intact 

 juveniles and is the measurement used through- 

 out. For fragmentary specimens, the standard 

 length was estimated from previously determined 

 relations between standard length and various 

 vertebral segments (Yoshida, 1968). A total of 

 127 juvenile albacore was found in the billfish 

 stomachs (Table 1). 



' National Marine Fisheries Service, Hawaii Area 

 Fishery Research Center, Honolulu, Hawaii 96812. 



Manuscript accepted June 1971. 



FISHERY BULLETIN: VOL. 69. NO. 4, 1971. 



'' For the purpose of this paper the term billfish, in 

 addition to the Istiophoridae, includes the swordfish, 

 Xiphias gladius. 



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