Table 2. --Comparison of size distributions (in cm.) from all 

 areas. Sampling period from January 27 to April 13 



The fact that we find approximately the 

 same size increments between modes in these 

 several areas (except the central equatorial 

 Pacific) could indicate a possibility of extensive 

 migration and intermingling of the stocks, how- 

 ever, morphometric studies (Royce 1953) indicate 

 little intermingling between areas as widely 

 separated as these. The distance between the 

 modes in the central equatorial distribution (fig. 

 10) suggests the absence of one of the dominant 

 size groups, i. e. , in the other three areas there 

 are dominant groups present between the central 

 equatorial modes at approximately 109 cm. and 

 147 cm. Whether or not these groups are annual 

 in occurrence is speculative, but the sinnilarity 

 in their positions and the dissimilarity in their 

 relative strength among areas suggests the possi- 

 bility of similar spawning and growing patterns 

 throughout this vast region as well as that of 

 extensive nnigration despite Royce's conclusions. 



DISCUSSION 



There is a consistent progression of 

 modes in size-frequency plots of Hawaiian longline- 

 caught yellowfin. It is unfortunate that large 

 samples of measurements separated by sex are 

 not available throughout the year so that the 

 nature of the apparent change in growth rate for 

 the latter half of each year could be more care- 

 fully analyzed. Such sannples might show this 

 change in growth rate to be associated with dif- 

 ferential nnigration patterns or the ingress of 

 slower growing fish. 



Kishinouye (1923), in speaking of 

 scombroids in general, says "Generally the 

 male fish come first, in the middle of the 

 fishing season the number of both sexes is 

 nearly equal, and at the end of the season the 

 female fish predominate. " This might account 

 for the apparent reduction in growth rate 

 except for the fact that the sex ratio appears 

 to be constant during the months of highest 

 availability, and during the period of changing 

 growth rate. 



Spawning may account for a reduced 

 growth in weight due to a physiological strain 

 on the female fish plus the loss of eggs. Van 

 Oosten and Hile (1949) conclude that "female 

 Lake Erie^ whitefish /Coregonus clupeiformis 

 (Mitchill)/ lose approximately 11 percent of 

 their weight at spawning" and it is well known 

 that checks which correlate well with spawn- 

 ing time are laid down on the scales of Sonne 

 species. The spawning period of Hawaiian 

 yellowfin agrees well with the tinne of change 

 in growth rate, but there is apparently no re- 

 sunnption of the prespawning rate as soon as 

 the spawning period is over. 



At the Equator the yellowfin size- 

 frequency distributions fronn any one area 

 consist of a series of dominant size groups 

 which do not appear to grow. The presence 

 of nnodes indicates a linnited spawning season 

 or perhaps an extended spawning season with 

 peaks of activity at certain tinnes, for it is 



11 



