PARRISH ET AL.: AGE DEPENDENT FECUNDITY IN NORTHERN ANCHOVY 



tivity, it is probable that the fishery undersamples 

 the active spawners. In addition, a proportion of the 

 commercial catches occur during the time of day 

 when the females do not have hydrated eggs. The 

 fishery data will therefore tend to underestimate the 

 spawning incidenca The total sea survey data will 

 also produce an underestimate as it includes samples 

 taken throughout the night. 



The combined fishery-sea survey data used in our 

 analyses will therefore provide only an index of the 

 daily spawning incidenca To evaluate the potential 

 net bias of this index we calculated the percentage 

 of females with maturity stages 5 + 6, in the com- 

 bined fishery-sea survey data, and the percentage 

 of females with day-1 postovulatory follicles, in the 

 histological data. To make the data comparable we 

 used the period 1977-84 and the months February- 

 April. The percentage of females with maturity 

 stages 5 + 6 and the percentage of females with 

 day-1 postovulatory follicles was 10.9 and 11.5%. Use 

 of the maturity stage data will therefore slightly 

 underestimate the daily spawning incidence (i.a, 

 10.9/11.5 = 0.948). 



Size Dependent Batch Fecundity 



Annual fecundity in the northern anchovy is 

 dependent upon the batch fecundity and the number 

 of spawnings per year. Batch fecundity is size depen- 

 dent and the best average estimate over six seasons 

 (Hunter et al. 1985) is given below. Note that Hunter 

 et al. found significant variation (ANOVA) among 

 years. 



batch fecundity = -1,104 + 614 (WT) 



where WT = female wet weight, minus ovaries, in 

 grams. During the spawning season ovary free 

 weight of northern anchovy is equal to 95% of the 

 total wet weight (Hunter and Leong 1981). Batch 

 fecundity, with the above relationships, for a typical 

 1-yr-old (12 g) and a typical 4-yr-old (24 g) are 5,896 

 eggs and 12,895 eggs. On a per unit weight basis 

 the 24 g fish would produce only 9.4% more eggs 

 than the 12 g fish. Age-dependent variations in 

 batch fecundity are therefore of only minor signifi- 

 cance in the relationship between spawning biomass 

 and annual fecundity. There is the possibility that 

 batch fecundity could vary over the spawning 

 season, and since we have shown an age-dependent 

 seasonality in the spawning incidence of northern 

 anchovy, this could potentially contribute to age- 

 dependent differences in annual fecundity. Hunter 

 and Leong (1981), however, found average batch 



fecundity to be essentially the same in samples taken 

 in January-February and in March- April. 



Size-Dependent Histology 

 Classes 



Hunter and Macewicz (1980) found no relationship 

 between size and the percentage of mature female 

 northern anchovy with day-1 postovulatory follicles. 

 Later work by Picquelle and Hewitt (1984) showed 

 that weight and spawning incidence were highly cor- 

 related in the northern portion of the central stocks 

 range. They stated that this implied that the larger 

 females spawned more frequently or that the 

 smaller females had a much shorter spawning 

 season. We analyzed the larger histology data set 

 now available and found that the percentages of 

 females with hydrated oocytes or with day-1 post- 

 ovulatory follicles, as well as the percentage of 

 females with maturity stages 5 + 6, were depen- 

 dent upon the size of the females (Fig. 9). 



80 



81- 



100 



101- 

 120 



121- 

 140 



141- 

 160 



LENGTH SLCMN; 



Figure 9.— The percentages of female northern anchovies with 

 hydrated eggs, with maturity stages 5 + 6, and day-1 histological 

 classes by size group. 



Age-Dependent Spawning Incidence 

 and Annual Fecundity 



To assess age-dependent, annual fecundity in the 

 central stock of northern anchovy we calculated the 



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