PARRISH ET AL.: AGE DEPENDENT FECUNDITY IN NORTHERN ANCHOVY 



ing is completed in the early morning (Fig. 6). This 

 implies that in the early evening maturity stages 5 

 + 6 can be used to estimate the spawning incidence; 

 however, within a few hours after sunset the per- 

 centage of females with hydrated eggs (i.e., stages 

 5 + 6) rapidly becomes an underestimate of the in- 

 cidence of spawning due to the completion of spawn- 

 ing. If only the females (n = 2,161) sampled between 

 the hours of 1800 and 2000 are considered, then the 

 percentage in maturity stages 5 + 6 (15.3%) is quite 

 close to the percentage of day-0 females calculated 

 for the total histology data set (15.9%). 



The variation throughout the night of the percent- 

 ages of the other maturity stages is also of interest 

 as it offers some insight into the meaning of maturity 

 stages in anchovy. Hunter and Macewicz (1980) 

 showed that spawning primarily occurs between the 

 hours of 1800 and 0200. In the sea survey data the 

 percentage of stages 5 + 6 falls from 15.3 to 1.6% 

 over this time period (Fig. 7). The expected matur- 

 ity stage that should increase over this time period 

 is stage 7 (i.e., spents: ovaries slack with residual 

 eggs). This, however, is not the case The percentage 

 of stage-7 females has very little variation over the 

 1900-0200 period; going from 2% at 1900 to 3.6% 

 at 0200. This suggests that residual eggs occur in 

 only a small percentage of anchovy and that stage 

 7 cannot be used to determine if an anchovy has 



spawned within 24 h. This is consistent with Stauf- 

 fer and Picquelle's (1980) observation that field- 

 spawned northern anchovy were found to release 

 nearly 100% of their hydrated eggs. The percentages 

 of the other maturity stages show considerable varia- 

 tion from 1900 to 0200 h. Stages in which the ovary 

 is small (i.e., 1 + 2) occur in about 37% of the females 

 in the early evening. This increases rapidly after 

 2300 and by 0200 these stages comprise about 46% 

 of the females. Stages 3 + 4, in which the ovaries 

 occupy from one half to two thirds of the ventral 

 cavity, occur in about 46% of females in the early 

 evening. This rises to a peak of about 54% at 2300- 

 2400 and then declines to about 49% at 0200. 



Our interpretation of the patterns exhibited by the 

 sea survey data is that the percentage of females at 

 stages 5 + 6 in the early evening (i.e., 15.3%) is a 

 valid estimate of the percentage of sampled females 

 with hydrated eggs. However, as the night progresses 

 the percentage of stages 5 + 6 declines. At the peak 

 of spawning, just before midnight, many females ap- 

 pear to be misidentified as stages 3 + 4. This could 

 occur if they had spawned part of their eggs before 

 they were captured and if the person making the 

 maturity stage determinations used the size of the 

 ovary, rather than the presence of hydrated eggs, to 

 determine the maturity stage After midnight an 

 increasing percentage of spawning females have 



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 £ 10 



HYDRATED EGGS 



STAGES 5+6 



1 I 1 1 1 1 1 1 — T 



1800 2000 2200 2400 200 



TIME OF NIGHT 



400 



1800 2000 2200 2400 200 

 TIME OF NIGHT 



400 



Figure 6.— The percentages of female northern anchovies with 

 hydrated eggs and with maturity stages 5 + 6, by time of night. 



Figure 7.— The percentages of grouped maturity stages for female 

 northern anchovies by time of night. (Two hour moving average.) 



511 



