62 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



o 



en 



UJ 

 Q_ 



JAN 



FEB MAR APR MAY JUfcl JUL AUG 



Figure 8.- 



-Percentages of fish with ovaries in the nonspawning, spawning, and spawned-out conditions, by months. The 

 number of fish included for each month is indicated at the top of each column. 



dition shows that no fish were in spawning con- 

 dition from December through March, and that 

 all were in that condition from May through 

 September. The curve (fig. 9) based on ratios 

 of ovary weight to fish weight, on the other hand, 

 only shows that there was more spawning in the 

 June to October period than in the rest of the 

 year. Although interpretation of the ratios may 

 make it possible to determine whether spawning 

 involved all fish in the June to October period 

 and none in the rest of the year, the regression 

 method much more definitely establishes time and 

 extent of spawning. 



JAN FEB MAP. APR MAT JUN JUL AUG SEP OCT NOV OEC 



Figure 9. — The 1950 spawning season of yellowfin tuna as 

 indicated by the mean ratios of ovary weight to body 

 weight for all fish. The data are grouped into semi- 

 monthly periods. 



FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 



Figure 10. — The spawning season of yellowfin tuna rep- 

 resented by the percentages of maturing fish in each 

 month, as determined by the ovary weight-fish weight 

 regressions. 



SPAWNING AND THE FISHING SEASON 



The period of spawning and the peak of the 

 fishing season so nearly coincide (fig. 11) that the 

 fishery appears to be based on a spawning run. 

 It should be remembered, however, that our use 

 of the term "spawning fish" includes fish with 

 well-developed ovaries that were not necessarily 

 fully ripe for spawning. One fully ripe ovary 

 was found among the samples taken. Fish that 

 are actually spawning either do not take the hook 

 or they migrate into deeper water outside the long- 

 lining grounds. 



