FISHERY BULLETIN: VOL. 84, NO. 4 



Table 2.— Numbers of female skipjack tuna in various spawning 

 and atretic states. The 8 collections taken in the South Pacific 

 between 20 October and 30 November 1984. 



'Atretic State 

 State 1 



State 2 



State 3 



no alpha stage atresia of yolked oocytes. 



alpha stage atresia of yolked oocytes present, but <50% 



affected. 



alpha stage atresia present, 50% or more yolked 



oocytes affected. 



no yolked oocytes present and beta stage atresia 



present. 



One female skipjack tuna in collection 4 was immature. 

 3 A female with hydrated oocytes and age h postovulatory follicles. 

 "Three of these females had oocytes in migratory nucleus stage. 

 5 Two of these females had oocytes in migratory nucleus stage. 



Five of these females had oocytes in migratory nucleus stage. 



be 0.071 (Cochran 1977; see methods). This means 

 that the average interval between spawnings 

 (1/0.85) was only 1.18 d. Only one female was imma- 

 ture, reducing the denominator for the above frac- 

 tion spawning from 87 to 86. If we consider only 

 those females with yolked oocytes and no or minor 

 atresia (atretic states and 1) the fraction spawn- 

 ing is 0.90, implying a mean interval of 1.11 d 

 between spawnings. This indicates that the spawn- 

 ing rate of female skipjack tuna in prime reproduc- 

 tive condition is very close to daily. 



High levels of ovarian atresia were much more 

 common among the 12 females taken in February 

 than those taken in October-November, indicating 

 that the February fish were nearing the end of their 

 spawning season. Females with highly atretic 

 ovaries (state 2) and postspawning ovaries (state 3) 

 constituted 66% of the fish in the February collec- 

 tions (Table 3), but they made up only 10% of the 

 fish taken in October-November. The February col- 

 lection was the only one taken by pole and line. It 

 is possible that pole-and-line fishing may be selec- 

 tive against spawning fish (Iverson et al. 1970; 

 Matsumoto et al. 1984) although some spawning fish 

 were taken in this collection. 



The most unusual feature of the February collec- 

 tion was that the spawning fraction was high, 0.25 

 for a group where 50% of the fish were in post- 

 spawning condition, had no yolked oocytes, and 

 were incapable of spawning (atretic state 3). The 

 spawning fraction was 1.0 for the three females with 

 no or minor atresia because all three had postovula- 

 tory follicles. Thus skipjack tuna with active ovaries 

 appear to spawn nearly every day. It appears that 

 those unable to maintain this rate may discontinue 

 spawning and resorb the ovary because females with 

 active ovaries, showing no evidence of spawning, 

 were rare in all collections. Postspawning females 



Table 3. — Numbers of female skipjack tuna in various spawning 

 and atretic states. This single collection was taken 23 February 

 1984. 



Collec- 

 tion 

 number 



Atretic 

 state 1 



Postovulatory 

 follicles 



12 h 



24 h 



Non- 

 spawning 



Total 

 mature 

 females 



1 





 1 

 2 

 3 

 Total 





 

 

 

 







1 



2 

 6 

 9 



2 

 2 

 2 

 6 

 12 



'Atretic State = no alpha stage atresia of yolked oocytes. 



State 1 = alpha stage atresia of yolked oocytes present, but <50% 



affected. 

 State 2 = alpha stage atresia present, 50% or more yolked 



oocytes affected. 

 State 3 = no yolked oocytes present and beta stage atresia 



present. 



900 



