FISHERY BULLETIN: VOL. 84, NO. 3 



of determining the number of spawnings per year. 

 The pioneering work by Hunter and Goldberg (1980) 

 and later studies based on this work clearly demon- 

 strate that, at least for many clupeids, the spawn- 

 ing incidence or spawning frequency can be deter- 

 mined with properly designed histological studies. 

 Unfortunately a research program designed to 

 determine age-specific reproductive potential would 

 be very expensive as it would require a field sam- 

 pling progam extending over the whole spawning 

 season, in many cases the entire year; and it would 

 require histological analysis and aging of a large 

 number of females, both quite labor intensive. 



It appears that the only way it may be possible 

 to determine age-specific reproductive potential for 

 many fishes is to use the approach developed here 

 which combines two methodologies: histological 

 assessment of ovaries because it unambiguously and 

 accurately measure spawning rate and a traditional 

 fishery sampling program which utilizes an inexpen- 

 sive rapid index of reproductive condition, such as 

 the maturity stage system or a gonado-somatic 

 index, in which thousands of specimens can be 

 processed. Whichever anatomical grading system is 

 used, its principal purpose would be to determine 

 the percentage of hydrated females. Most of the 

 maturity stages (i.e., 1-4, 7) in the system used for 

 northern anchovy are only of value in describing the 

 seasonality of spawning. The only stages (i.e., 5 and 

 6) which can be used to determine the number of 

 spawnings are those in which the eggs are hydrated, 

 and they can be directly used as an index in north- 

 ern anchovy because it is known that the duration 

 of hydrated eggs in the ovary is <24 h. The tradi- 

 tional fishery sampling program may, as in the case 

 for northern anchovy, already be available. If this 

 is the case the principal work will be to calibrate 

 properly the maturity stage or gonado-somatic in- 

 dex with the histological analysis. For this approach 

 to work the fishery must, of course, take hydrated 

 females. 



CONCLUSIONS 



It is important for those managing fisheries which 

 are susceptible to recruitment overfishing to realize 

 that the alteration in the age structure of a stock 

 that occurs under heavy exploitation may have 

 greater effects on the total fecundity and seasonality 

 of spawning than previously recognized. Manage- 

 ment strategies which decrease the exploitation of 

 older, more fecund females could increase yields and 

 also provide increased protection against recruit- 

 ment overfishing. In northern anchovy there is the 



additional factor that the sex ratio in the fishery is 

 age dependent (i.e., the female:male ratio for 1-yr- 

 old anchovy in the San Pedro fishery is 0.83:1, 

 whereas that for 4+ yr-olds is 2.01:1). When this 

 factor is multiplied by the difference in the fecun- 

 dity of the two age groups, it is apparent that the 

 catch of a ton of 4 + yr-old northern anchovy reduces 

 the reproductive potential of the stock 7.3 times as 

 much as the catch of a ton of 1 -yr-old fish. 



ACKNOWLEDGMENTS 



We gratefully acknowledge John Hunter and 

 Beverly Macewicz for allowing us to use their exten- 

 sive data on the histology of the ovaries of northern 

 anchovy and Carol Kimbrell for providing us with 

 the computer files. John Hunter also provided con- 

 siderable input to the development of the work and 

 edited the manuscript. We would also like to thank 

 Eric Knaggs, Eugene Fleming, and John Sunada for 

 providing us with the anchovy fishery data and Ken- 

 neth Mais for providing the sea survey anchovy data. 



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