158 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Joil: 



[FEMALES (N=57) 

 MALES (N=23l) 



Jal 



Jli. 



Ill 



i 



IUiIl 



M 





H a M 



1l_Hi I I I I gii 



FORK LENGTH IN CENTIMETERS 



Figure 9. — Size of albacore taken in the Hawaiian longline fishery, 1955-56. 



than 110 cm. in the South Pacific. A similar 

 lack of large males was fpund in samples from the 

 central equatorial Pacific (Otsu and Uchida, 

 1959b); the significance of this difference in size 

 composition between Hawaiian waters and more 

 southern areas is not known. Further study 

 is needed concerning the distribution of these 

 large males. 



The most highly developed ovaries reported to 

 date have come from waters around the Hawaiian 

 Islands in the North Pacific (Otsu and Uchida, 

 1959b) and from the area of the Sunda Islands in 

 the Indian Ocean (Ueyanagi, 1955). None as 

 advanced in development has yet been collected 

 from the central equatorial Pacific or the South 

 Pacific Ocean. The fish taken in the Indian 

 Ocean are also large, falling intermediate be- 

 tween the Hawaiian and the central South Pacific 

 albacore. Despite the apparent absence of the 

 group of largest males in the central South Pacific, 

 it appears certain that the males available to the 

 longline fishery there are generally all adults 

 which are already capable of spawning. 



DISCUSSION 



Our data suggest that albacore in the central 

 South Pacific Ocean spawn during the southern 

 summer months. This finding is based on the 

 percentage occurrence of ovaries in the late 

 developing stage for each month in which samples 

 were obtained. Since only six pairs of ovaries 

 were found in which development of the ova was 



beyond the late developing stage, the occurrence 

 of ovaries in the late developing stage was used 

 as an index of spawning fish. The inherent 

 weakness in our assumption, particularly in 

 assessing exact spawning grounds and spawning 

 seasons, is that the time of spawning cannot be 

 determined precisely from the occurrence of fish 

 in this stage of ovary development, in the absence 

 of any knowledge of the rate of ova development. 

 The gradual increase in the proportion of late 

 developing ovaries in the monthly samples from 

 the low point in May to a peak in December, 

 with a gradual decrease thereafter, suggests 

 that spawning must take place during the southern 

 summer months. Depending upon the rate of 

 ova development, albacore may be spawning 

 during only a portion of that period, and that 

 portion may be towards the end, when the per- 

 centage of developing ovaries is decreasing. 



The weakness in the data is also evident in 

 attempting to determine the spawning grounds. 

 Our data suggest that the bulk of the spawning 

 activity is confined to the north of 20° S. latitude. 

 The data also indicate no east-west differences in 

 spawning activity within the extent of our sam- 

 pling (fig. 5). In the absence of ovaries of more 

 advanced development, these results may be ques- 

 tionable. There may be sufficient time between 

 the late developing and ripe stages to permit con- 

 siderable migration. No purposeful spawning 

 migration can be detected from the data at hand. 

 Until more definite findings are made by the cap- 



