YOSHIDA: JUVENILE ALBACORE IN SOUTH PACIFIC OCEAN 



LENGTH OF JUVENILES 



The juvenile albacore in the billfish stomachs 

 ranged from 26 to 358 mm (Figure 1). Two 

 length groups were apparent in the' length-fre- 

 quency distribution: one with a mode at 110 mm 

 and the other at 310 mm; another length group 

 was suggested between 200 and 250 mm. 



In the course of the study it became apparent 

 that the larger juveniles were being taken be- 

 tween lat 20° and 30° S. To determine if dif- 

 ferences existed in juvenile sizes by latitude, 

 lengths were plotted against latitude of capture 

 (Figure 2) . The smallest individuals were taken 

 north of lat 10° S and the largest south of lat 

 20° S. No specimens smaller than 290 mm were 

 taken south of lat 20° S. The juveniles between 

 lat 10° and 20° S were slightly larger (mean SL 

 120 mm) than those taken north of lat 10° S 

 (mean SL 94 mm). The mean standard length 

 of those from south of lat 20° S was 324 mm. 



In contrast to the latitudinal differences in 

 juvenile length, no longitudinal trends in length 

 were evident. Juveniles larger than 300 mm 

 were taken in the eastern as well as the more 

 westerly portion of the area sampled. 



MIGRATION OF JUVENILES 



The differences in the lengths of the albacore 

 in the three latitudinal bands may be caused 

 by the migration of the juveniles. The increase 

 in length of juveniles from north to south and 

 the absence of any longitudinal trends in length 

 suggest a southward migration. After attain- 

 ing a length of nearly 200 mm the juveniles that 

 originate between the equator and lat 10° S prob- 

 ably start migrating south. They apparently 

 continue to move southward as they grow. This 

 migration would explain the absence of large 

 (>250 mm) juveniles north of lat 20° S. 



These observations on the suspected migration 

 pattern of juvenile albacore fit well with the 

 accumulated information on the biology of al- 

 bacore in the South Pacific. Observations on 

 the length composition of commercial catches 

 of albacore in the South Pacific indicate latitu- 

 dinal differences in the size of albacore. Adult 

 albacore tend to be small north of lat 15° S and 



NUMBER 

 18 



50 100 150 200 250 300 350 



STANDARD LENGTH (mm) 



Figure 1. — Length-frequency distribution of juvenile al- 

 bacore in the South Pacific. 



120 160 200 240 



STANDARD LENGTH (mm) 



Figure 2. — The length of juvenile albacore plotted 

 against latitude of capture. 



largest between lat 20° and 25° S. They are 

 smaller again south of lat 25° S (Otsu and Su- 

 mida, 1968) . Length-frequency data published by 

 the Nankai Regional Fisheries Research Labora- 

 tory ( 1959) show that albacore as small as 490 to 

 500 mm are caught on longlines south of lat 

 30° S. Thus, it could be that the juveniles move 

 southward as they grow and are first taken by 

 the longline fishery as preadults in the higher 

 latitudes in the South Pacific. A similar pat- 



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