In samples containing mostly males (mean sex 

 ratio = 0.25), nearly 40% of the females spawned 

 on the night of capture, whereas in samples con- 

 taining mostly females (mean sex ratio = 0.84), 

 only 10% of the females spawned on the night of 

 capture (Table 5). A chi-square test indicated that 

 the proportion of females spawning on the night of 

 capture differed among the three classes of sex 

 ratios (P<0.001) but no difference existed for 

 females with 1-day-old postovulatory follicles. 

 Therefore, most spawning occurred in male domi- 

 nated schools but females that spawned on the 

 previous night occurred in about equal propor- 

 tions in all schools. 



That groups of pelagic spawners could be male 

 dominated is indicated by the reproductive be- 

 havior of another pelagic spawner, the Pacific 

 bonito, Sarda chiliensis, described by Magnuson 

 and Prescott (1966). They reported that during 

 courtship, groups of males closely follow a single 

 female. If male anchovy show similar behavior, 

 then trawl collections taken at the time of spawn- 

 ing might be male dominated. To explain the 

 dominance of females in commercial catches, 

 Klingbeil (1978) suggested that male-dominated 

 groups may not form the large dense schools 

 necessary for effective purse seining. It seems 

 reasonable that actively spawning (male- 

 dominated) groups, would not be as likely to pre- 

 serve the density or the integrity of the school as 

 well as nonspawning groups. Thus, the variability 

 in sex ratio of anchovy schools may be attributable 

 in part to reproductive behavior, that is, the for- 

 mation of male-dominated spawning groups 

 which may be smaller and less dense than com- 

 mercial schools. The female component of such 

 groups would be expected to change from day to 

 day because after 24 h, spawned out females oc- 

 curred with equal frequency in all samples regard- 

 less of sex ratio. 



Growth of Oocytes 

 Incidence of postovulatory follicles indicated 



FISHERY BULLETIN. VOL, 77. NO. 3 



that in February 16% of the females spawned 

 daily or an individual female spawned on the av- 

 erage once every 6.25 days. In the fecundity sec- 

 tion that follows, we show that nearly all of the 

 eggs in the most advanced mode are spawned in 

 one night. Thus, a new mode of eggs must mature 

 every 6-7 days to maintain a spawning frequency 

 of 16%. In the laboratory, spawning begins when 

 the average diameter of the eggs in the most ad- 

 vanced mode is between 0.6 and 0.7 mm. Thus the 

 eggs remaining in the ovary after spawning must 

 attain this size in 6-7 days. 



To determine if such rapid oocyte growth 

 seemed reasonable, we estimated the mean 

 diameter of eggs in the most advanced mode and in 

 the second mode for some of the females taken in 

 February and March. Females with hydrated eggs 

 were placed in the same class as those with new 

 postovulatory follicles because hydrated eggs 

 were not included in this analysis. The number of 

 females analyzed and the elapsed time from 

 spawning were: elapsed time day (hydrated eggs 

 and new postovulatory follicles) n = 43; elapsed 

 time 1 day (1-day-old postovulatory follicles) 

 n = 35; and elapsed time 3.5 days (nonspawning 

 mature females) n = 38. The time from spawning 

 in the last class was unknown. We assigned the 

 midpoint of the interval 2-5 days to this class be- 

 cause all fish classified as nonspawning would fall 

 within this interval if the spawning cycle were 6 

 days. The mean diameter of oocytes in the second 

 mode was estimated only for nonspawning 

 females. In these more mature females, most of the 

 oocytes in the second mode were >0.2 mm, 

 whereas, in less mature fish a significant propor- 

 tion of the oocytes in the second mode were <0.2 

 mm, and thus below the lower limit of our mea- 

 surements. 



The average diameter of eggs in the ovary in the 

 most advanced mode immediately after spawning 

 was 0.46 mm; 1 day after spawning it had in- 

 creased to 0.51 mm and was 0.59 mm in nonspawn- 

 ing females. Figure 4 illustrates how growth in the 

 diameter of eggs in the most advanced mode and 



Table 5.— Sex ratio in samples (femalesrt males + females)) and percent of spawning northern anchovy 

 taken in February 1978 off southern California. 



'Twenry-five fish per sample were used to calculate sex ralio and 10 or 1 1 females were examined histologically. 

 ^Includes females with hydrated eggs and those witti recent postovulatory follicles- 

 ^Females with 1-day-old postovulatory follicles. 



648 



