160 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



each is distributed in an approximate mirror image 

 of the other. In the North Pacific, only the alba- 

 core in temperate waters are being exploited com- 

 mercially. Albacore are taken incidentally to 

 other species and in small numbers in subtropical 

 and tropical watere, i.e., between 25° N. and the 

 Equator. 



Spawning is believed to occur in subtropical 

 waters, roughly between 10° N. and 25° N. lati- 

 tude in the western Pacific during the northern 

 summer months. The situation is somewhat dif- 

 ferent in the South Pacific. The major exploita- 

 tion in the South Pacific at present is of the sub- 

 tropical resource of albacore in the area between 

 10° and 30° S. latitude. Furthermore, the only 

 fishery equivalent to the North Pacific temperate 

 water fisheries is the relatively small coastal fishery 

 of Chile. However, data published by Japan's 

 Nankai Regional Fisheries Research Laboratory 

 (1959), reproduced here as figure 11, indicate the 

 presence of smaller albacore south of the present 

 central South Pacific fishing grounds (south of 

 30° S. lat.). These albacore appear to be the 

 counterpart of the northern temperate-zone alba- 

 core. While there is no extensive fishery for 

 albacore in these southern temperate waters today, 

 there is a likelihood that a large resource is present 

 (Suda, 1956). 



While not exactly alike, the distributions follow 

 a similar pattern on both sides of the Equator, 

 with the smaller nonspawning fish occurring in 

 the higher latitudes, and the larger spawning fish 

 in the lower latitudes. Because of the general 

 scarcity of albacore in equatorial waters, there 

 appears little likelihood of any great interchange 

 of fish between the two groups. 



SUMMARY 



This study is based on the examination of 

 1,772 pairs of albacore gonads collected at the 

 tuna cannery in American Samoa between August 

 1957 and September 1958. The 782 female and 

 990 male gonads were collected randomly from 

 256 landings made by Japanese longline vessels. 



Upon receipt of the frozen gonads from Samoa, 

 they were thawed and preserved in 10-percent 

 formalin. Each pair was weighed, and ovary 

 sections were examined microscopically. The 

 stage of development was determined on the 

 basis of the general appearance and characteris- 



tics of the largest ova present. No detailed 

 examination was made of the testes. 



Only six ovaries were found to be in the 

 advanced stage of development; these contained 

 ova which were just beginning to take on the 

 semitransparent appearance characteristic of this 

 stage. The remainder of the ovaries were in 

 all degrees of development preceding this stage. 



From the monthly occurrence of the more 

 mature stages (late developing and advanced), 

 it was found that the peak of spawning activity 

 in the central South Pacific is during the southern 

 summer months at some time between September 

 and March. This is in contrast to the albacore 

 of the North Pacific, which appear to spawn 

 during the northern summer months. 



The examination of the data for areal variations 

 in ovary development revealed no clear longitu- 

 dinal differences. Latitudinally, nearly all of the 

 more highly developed ovaries were obtained 

 from fish captured north of 20° S., with the bulk 

 between 10° S. and 20° S. latitude. The data 

 indicated that there is little, if any, spawning 

 in areas south of 20° S. latitude. 



Plotting the developmental stage of each ovary 

 against fish size revealed ' that female albacore 

 become sexually mature and spawn for the first 

 time at a size of about 86 cm. This is a slightly 

 lower estimate of the minimum size of first spawn- 

 ing than previously reported (90 cm.). 



The sampled fish ranged between 72 and 110 

 cm. (15 and 64 lbs.). In comparison, the Hawai- 

 ian albacore which are believed to be a p.irt of 

 the reproductive segment in the North Pacific 

 are larger, ranging between 93 and 128 cm. (33 

 and 93 lbs.). A closer examination of the data 

 shows that females are of comparable sizes in 

 both areas, but that the very large males are 

 missing from the South Pacific samples. It 

 appears certain, however, that the males avail- 

 able to the longline fishery in the central South 

 Pacific are nearly all adults which are already 

 capable of spawning. The significance of this 

 size difference in the males between the two areas 

 is not clear. 



Although the data are such that the precise 

 spawning area or season could not be determined, 

 the fact that the peak of spawning in the South 

 Pacific occurs during the southern summer months, 

 as contrasted with the northern summer spawn- 



