HUNTER and GOLDBERG: SPAWNING INCIDENCE OF NORTHERN ANCHOVY 



2 



1.5 



1.0 



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EGG DIAMETER 

 0.30 - 0.50 mm 



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0.43 mm 



I I I I I I I I I I I I 



10 



15 20 25 30 35 



2.0 I- 



1,5 - 



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1.0 



I 0.5 

 > 



o 

 ao 



2.5 



EGG DIAMETER 

 0.51 - 0.60 mm 



2.0 



1.0 



0.5 



0.55 mm 



I I I I I I I ''' I ' I I I I I I I I I I I ' I I I I 'i I ' 

 5 10 15 20 25 30 35 



EGG DIAMETER 

 0.61 - 0.76mm 



0.65 mm 



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 5 10 15 20 25 30 35 



OVARY FREE FEMALE WEIGHT (g) 



Figure 5. — Relation between wet weight of ovary and o- ary- 

 free wet weight of female northern anchovy classed into three 

 groups, based on the mean diameter of eggs m the most advanced 

 mode. Each pomt is a value for a single female. The lines repre- 

 sent multiple regressions, described in the text, for the mean egg 

 diameters given by the arrows. 



gions or at depths not sampled by the" trawl or 

 commercial purse seine. Studies need to be con- 

 ducted at other times of the year and employing 

 other sampling techniques to answer these ques- 

 tions. 



This paper also describes a new method for es- 

 timation of batch fecundity in a multiple spawn- 

 ing fish. Our estimation for northern anchovy 

 based on hydrated eggs ( 389 eggs/g female weight, 

 less ovary), was substantially less than that of 

 MacGregor (1968) (606 eggs). This difference 

 could be attributed to annual variation in fecun- 

 dity because variations of this size are known to 



occur in fishes (Bagenal 1973). On the other hand, 

 our selection of females on the basis of reproduc- 

 tive state also may have been responsible for at 

 least part of the difference. Our estimates for 

 females that had recently spawned (day and day 

 1 postovulatory follicles. Table 6i were close to 

 MacGregor's estimate. In recently spawned 

 females, modal groups of eggs were less distinct, 

 and often one mode was considered to exist when 

 the eggs may have been destined to form two 

 spawning batches. If MacGregor (1968) used such 

 females, this could explain in part why his esti- 

 mate was higher than our estimates based on hy- 

 drated eggs or on fish classed as nonspawning. In 

 addition, our technique of partitioning eggs occur- 

 ring between two modal groups according to an 

 assumed normal distribution may have decreased 

 our estimate somewhat relative to past methods. 

 Use of hydrated eggs avoids these problems, but it 

 does require histological examination to insure 

 that none of the females used for the estimate have 

 begun ovulation. Apparently, some of the females 

 we captured were spawning because their ovaries 

 contained many new postovulatory follicles as 

 well as many hydrated eggs. We usually examined 

 only one set of histological sections to determina- 

 tion if ovulation had occurred; histological exami- 

 nation of an entire ovary was impractical. We be- 

 lieve our examination was adequate because our 

 estimate based on hydrated eggs was close to the 

 one based on females with the most advanced 

 ovaries (nonspawning). 



In addition to the obvious application to the 

 estimation of spawning biomass, this work pro- 

 vided insights into the reproductive biology of E. 

 mordax. The high spawning frequency, the ability 

 to rapidly mature new batches of yolked oocytes. 

 and the long breeding season of the northern an- 

 chovy (Lasker and Smith 1977), indicate that 

 energy reserves and the availability of food may 

 set the limit to the number of spawnings and hence 

 to total fecundity. The analysis has also provided a 

 possible explanation for the variability in the sex 

 ratio of catches of anchovy. 



ACKNOWLEDGMENTS 



We thank Kenneth Mais (California Depart- 

 ment of Fish and Game) for providing the speci- 

 mens and data on sexual composition of schools 

 from his February 1978 cruise. We are indebted to 

 Roger Leong (Southwest Fisheries Center 

 ( SWFC ) ) who maintained and spawned anchovy in 



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