HUNTER and MACEWICZ: ATRESIA IN NORTHERN ANCHOVY OVARY 



TABLE 6. — Percentage of mature northern anchovy females in two length classes with 

 atretic ovaries. Females from north of Point Conception and groups with fewer than nine 

 females per length class excluded. 



2m, 



m  = mature nonspawning females, and m = females with 1-d-old postovulatory follicles. 



day for the two length classes to test this assump- 

 tion. We used the Stauffer and Picquelle (footnote 

 3) method for estimating spawning fraction as it 

 corrects for biases in the numbers of females with 

 hydrated eggs, i.e., 



M, 



F = 



2M, + m 



li ni 



where F = fraction of females spawning per day, 

 M^^ = number of females with 1-d-old postovula- 

 tory follicles, and m = number of mature females 

 with no recent spawning history (females with 

 postovulatory follicles or hydrated eggs are 

 excluded). Examination of Table 6 indicates that 

 differences in spawning fraction between the two 

 size classes of females were much less distinct 

 than were the differences in ovarian atresia. 

 Using only the 8 cruises in which the numbers of 

 females in each of the two length classes exceeded 

 10, the mean difference in spawning fraction (frac- 

 tion for large females — fraction for small females) 

 for the set of 8 cruises was +3.76% with 95% C.I. 

 ±3.50% indicating a small difference in spawning 

 frequency between the two length classes that is 

 just barely significant at the 5% level. We believe 

 the reason that differences in atretic fraction be- 

 tween large and small females are much more 

 consistent than those in spawning fraction is that 

 spawning fraction has a greater variability and a 

 much more limited dynamic range than does the 

 atretic fraction. Spawning fraction varies from to 

 about 16% and may be affected by time of day and 

 schooling behavior (Hunter and Goldberg 1980). 

 Atretic fraction varies from to nearly 100%, 



is not linked to reproductive behavior, and conse- 

 quently, is probably not affected by time of day or 

 schooling. 



DISCUSSION 



Evaluation of Atretic Classification 



Our objective was to evaluate the use of ovarian 

 atretic states to characterize the reproductive bi- 

 ology of northern anchovy populations. We in- 

 cluded in our analysis of laboratory data many 

 atretic characteristics not used to construct the 

 three atretic states utilized in the analysis of sea 

 data. These additional characters could be used to 

 create additional states or to more precisely de- 

 limit the existing ones. Our selection of charac- 

 teristics was based in part on ease of identification 

 since for population work thousands of histologi- 

 cal sections were examined. Other considerations 

 include the fact that statistical analysis indicated 

 that classifiers frequently confused beta stage 

 atretic follicles in yolked ovaries with postovula- 

 tory follicles older than 24 h, and, as a conse- 

 quence, beta atresia was not used as a diagnostic 

 character in ovaries with yolked oocytes. Alpha 

 stage atresia was the most useful atretic stage 

 because the type of oocyte (yolked) undergoing 

 atresia is still discernible. In addition, alpha stage 

 atretic oocytes can be easily distinguished from 

 postovulatory follicles whereas this is not the case 

 for later atretic stages. 



Three atretic states were defined and applied to 

 sea data. The incidence of all three atretic states 

 combined was a sensitive index of the reproductive 

 state of the population over the spawning season. 



133 



