SPAWNING OF YELLOWFIN TUNA 



257 



Table 2. — Data on yeltovifin tuna specimens from the central equatorial Pacific for which maturity determinations were made 



in Ike field — Continued 



Additional data (table 3) are available from 

 field observations reported by the Iwate Prefecture 

 Fishery Experiment Station (1953a and 1953b), 

 which were obtained from Japanese longline 

 expeditions into this area. As with the POFI 

 field observations, the stages of maturity were 

 combined into two groups, "active" and "in- 

 active", and the "spent" category was disregarded. 

 Other pertinent information found in these reports 

 is as follows: Tlie fishing area for the April cruise 

 was between latitudes 9° N. and 11° N. and 

 longitudes 170° W. and 173° W. Fish caught on 

 this cruise ranged from 110 to 150 cm. in length, 

 with only one fish measuring less than 120 cm. 

 Fishing during June and July was done at 3° N. 

 to 4° X. and 175° W. to 177° W. Fork lengths 

 ranged fi'om 114 to 173 cm., with only two fish 

 measuring less than 120 cm. Eighty percent of 

 the fish were caught in June, and the rest were 

 caught in July. 



Table 3. — A^umber of yellowfin tuna in various stages of 

 maturity, according to Iwate Prefecture Fishery Experiment 

 Station 



Note.— For further data see station reports (1953a and 1953b). 



SIZE OF FISH AT FIRST SPAWNING 



To determine the size of first-spawTiing fish, 

 the fork lengths collected by POFI were grouped 

 into classes of 10 cm., and the percentage of fish 

 in the "active" category (maturing and ripe 

 stages), as determined by ovary examination, was 

 calculated for each lengtli class. The results, 

 illustrated in figure 1 , show t hat all the fish smaller 

 than 70 cm. were in a nonspawning condition. In 

 the 70-to-79-cm. class (about 15 to 22 lbs.), 6.9 



